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    An HF Radar System for Ionospheric Research and Monitoring TECHNICAL MANUAL Operation and Maintenance Document Version 1.0 University of Massachusetts Lowell Center for Atmospheric Research 600 Suffolk Street Lowell, Massachusetts 01854 http://umlcar.uml.edu Telephone: (978) 934-4900 Facsimile: (978) 459-7915 E-Mail: Bodo_Reinisch@uml.edu Distribution A: “Approved for public release”. “UMLCAR Intellectual Property. Not for secondary distribution or replication, in part or entirety.” DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL REVISION LOG This log identifies those portions of this document which have been revised since the original issue released on January 28, 2009. Rev. Date Description IR 01-28-09 Initial release Initiator DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL SECTION 1 GENERAL SYSTEM DESCRIPTION _______________________________________________________________________________ SECTION CONTENTS Page SECTION 1 1-1 CHAPTER 1 THE DIGISONDE 4D ............................................................................................ 1-3 ORGANIZATION OF THE MANUAL ......................................................................................................... 1-3 DIGISONDE FAMILY OF IONOSPHERIC SOUNDERS........................................................................... 1-3 GENERAL DESCRIPTION ........................................................................................................................ 1-4 Digisonde 4D Block Diagram ................................................................................................................ 1-6 SPECIFICATIONS ..................................................................................................................................... 1-9 CHAPTER 2 METHODOLOGY, THEORETICAL BASIS AND IMPLEMENTATION .............. 1-12 BACKGROUND: IONOSPHERIC PROPAGATION OF RADIO WAVES................................................ 1-12 MOTIVATION FOR A SMALL FLEXIBLE IONOSPHERIC SOUNDER .................................................. 1-13 SIGNAL PROCESSING IN DIGISONDE 4D ........................................................................................... 1-14 General Considerations....................................................................................................................... 1-14 Coherent Pulse Integration in Time Domain ....................................................................................... 1-15 Coded Pulses to Facilitate Pulse Compression Radar Techniques ................................................... 1-15 Coherent Spectral Integration ............................................................................................................. 1-25 Complex Windowing Function ........................................................................................................ 1-28 Multiplexing.......................................................................................................................................... 1-29 Radio Frequency Interference Mitigation (RFIM) ................................................................................ 1-30 Angle of Arrival Measurement Techniques ......................................................................................... 1-33 Digital Beamforming (aperture resolution technique) ..................................................................... 1-35 Drift Mode – Super-Resolution Direction Finding ........................................................................... 1-38 Two Frequency Precision Ranging Mode ........................................................................................... 1-40 Passive RF Sensing Measurements ................................................................................................... 1-42 RF SYSTEM DESIGN CONSIDERATIONS............................................................................................ 1-45 BIBLIOGRAPHY ...................................................................................................................................... 1-47 SECTION 1 GENERAL SYSTEM DESCRIPTION 1-1 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL List of Figures Figure 1-1: Digisonde 4D Figure 1-2: Evolution of the Digisonde Figure 1-3: Magnetic Loop Turnstile Antenna with attached preamp module Figure 1-4: Block diagram of Digisonde 4D Figure 1-5: Main Chassis of the Digisonde 4D Figure 1-6: Power Amplifier Chassis of the Digisonde 4D Figure 1-7: Sounder Transceiver Sub-system (Rear View) Figure 1-8: Six-Dimensional Ionogram Figure 1-9: Generation of a Bi-phase Modulated Spread Spectrum Waveform Figure 1-10: Spectral Content of a Spread-Spectrum Waveform Figure 1-11: Natural Timing Limitations for Monostatic Vertical Incidence Sounding Figure 1-12: Conversion to Baseband by Undersampling Figure 1-13: Illustration of Complementary Code Pulse Compression Figure 1-14: Resolution of Overlapping Complementary Coded Pulses Figure 1-15: Autocorrelation Function of the Complementary Series Figure 1-16: Eight Coherent Parallel Buffers for Simultaneous Integration of Spectra Figure 1-17: VI Ionogram Consisting of Amplitudes of Maximum Doppler Lines Figure 1-18: Wideband received signal spectrum contaminated by interferences and background noise. Figure 1-19: Spectrum of the received signal without interferer (top) and with interferer (bottom). Figure 1-20: Spectrum of a truncated CW signal. Figure 1-21: Angle of Arrival Interferometry Figure 1-22: Antenna Layout for 4-Element Receiver Antenna Array Figure 1-22: Seven digitally synthesized beams for the angle of arrival measurement in ionogram mode List of Tables Table 1-1: Digisonde 4D specifications Table 1-2: RFIM Procedure Steps 1-3 1-4 1-5 1-6 1-8 1-8 1-9 1-15 1-17 1-18 1-19 1-20 1-22 1-23 1-24 1-28 1-30 1-31 1-32 1-33 1-34 1-35 1-36 1-9 1-33 1-2 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE CHAPTER 1 THE DIGISONDE 4D DIGISONDE 4D SYSTEM MANUAL Figure 1-1: Digisonde 4D ORGANIZATION OF THE MANUAL 101. The Digisonde 4D manual has 6 sections: a. Section 1 provides general description of the Digisonde 4D sounder and background information on ionospheric sounding and relevant signal processing techniques. b. Site preparation and installation instructions are provided in Section 2 of this manual. c. Operating instructions are given in Section 3. d. A full technical description of the sounder is provided in Section 4 (hardware) and Section 5 (soft- ware). e. Instructions for organisational and depot level maintenance plus reference to technical data required to support depot level fault finding and repair of sub-assemblies are contained in Section 6. DIGISONDE FAMILY OF IONOSPHERIC SOUNDERS SECTION 1 GENERAL SYSTEM DESCRIPTION 1-3 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 102. The Digisonde 4D is the latest digital ionosonde that the University of Massachusetts Lowell Center for Atmospheric Research (UMLCAR) developed during 2004-2008 (Figure 1-2). While preserving the basic principles of the Digisonde family – the Digisonde 128, the Digisonde 256, the Digisonde Portable Sounder DPS-1, and the DPS-4 – the Digisonde 4D model introduces a number of important hardware and software changes that implement the latest capabilities of new digital RF circuitry and embedded computers. The “D” in the new model refers to the digital transmitters and receivers in the Digisonde 4D, which uses digital up- and downconverter IC chips, the Graychip GC5016 and the Analog Devices AD9857, that implement the classic functions of radio transmitters and receivers by numeric techniques. It also uses new software solutions for data acquisition, hardware control, user commanding, and data processing. Figure 1-2: Evolution of the Digisonde GENERAL DESCRIPTION 103. Vertical radio sounding makes use of the fact that radio waves are reflected in the ionosphere at the height where the local cutoff frequency equals the frequency of the radio wave. The original analog ionosondes used for the sounding ever since Breit and Tuve described the concept in 1926 started to be replaced by digital instruments in the 1970s. Modern digital ionosondes are highly flexible HF radar systems tasked to reliably describe the status of the ionospheric density distribution on a continuous basis. Robust automated operation is a sine qua non for the monitoring function of the ionosonde, and measuring flexibility and precision are required for research applications. 104. Unlike incoherent scatter radar systems, ionosondes must be built at low cost and easy to install to make operations at many sites around the world feasible. As for the previous DPS models, the Digisonde 4D uses one simple crossed delta or rhombic antenna for transmission, and an array of four small crossed loops for reception. The integrated transceiver package of Digisonde 4D is shown in Figure 1-1, and one of the four crossed magnetic dipole receive antennas in Figure 1-3. 1-4 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 1-3: Magnetic Loop Turnstile Antenna with attached preamp module 105. Noteworthy new technology involved in Digisonde 4D system includes:  Analog Devices AD9857and Graychip GC5016 digital up- and down-converters  Fast 16-bit A/D converters for the digital receivers  Electronically switched active crossed loop receiving antennas  15 dB signal processing gain from phase coded pulse compression  21 dB additional signal processing gain from coherent Doppler integration  Up to 35 dB signal gain via RF Interference Mitigation algorithm  Two embedded computing platforms for data acquisition, hardware control, user commanding, data processing, storage, publishing, and dissemination  Compact DC-DC converters allowing operation on one battery  Software implementation of the signal processing functions applied to the time domain data  Automatic ionospheric layer identification and parameter scaling by an embedded expert system ARTIST 5  World-wide web access to real-time measurement data SECTION 1 GENERAL SYSTEM DESCRIPTION 1-5 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Digisonde 4D Block Diagram 106. Figure 1-4 shows the Digisonde 4D block diagram identifying the Digital Transmitter card, the Digital Receiver card, the Preprocessor card, four tracking filters, two 150 W Power Amplifiers with half-octave filters, and two embedded computers responsible for hardware control and data acquisition (Control Platform) and data processing and remote access (Data Platform). Figure 1-4: Block diagram of Digisonde 4D 1-6 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 107. The new 16-bit analog-to-digital converters (ADCs) and the digital receivers provide increased precision for amplitude and phase measurements and reduced temperature sensitivity. Since the Digisonde 4D must operate over a large frequency band of more than 8 octaves (from 0.1 MHz to 30 MHz), it is important to protect the ADCs from saturation by strong interferers operating in this large band. Saturation of the ADC would destroy the narrowband filtering of the digital receiver. An analog tracking filter in combination with automatic digitally controlled amplifier gain at the receiver input limit the ADC input voltages to specified value. 108. The physical dimensions of the Digisonde 4D remain unchanged since Digisonde Portable Sounder was introduced in 1990, consisting of two 19” chassis, one housing the two-channel transmitter power amplifiers and half-octave filters, the other the signal synthesizers, receivers, and digital signal processors. The system compensates for a low power transmitter (300 W vs. 10 kW for original Digisonde 128 and 256 models) by employing intrapulse complementary phase coding with digital pulse compression, Doppler integration, and the patented Radio Frequency Interference Mitigation algorithm RFIM which enhances the processing gain by 35 dB. 109. The Main (upper) Chassis (see Figure 1-5) comprises the following functional assemblies: a. Cardcage with Digisonde 4D electronics i. Digital transmitter / timing card ii. Digital receiver card iii. Four analog tracking filter cards (“tuners”) iv. Pre-processor card v. Built-In Test card b. Backplane with 61.44 MHz Master Frequency Standard c. Two embedded computer platforms (Control platform and Data platform) i. DVD R/W mass storage drive ii. Removable Hard Disk tray d. Power distribution board with DC/DC converters e. Antenna switch f. Three axial fans 110. The Power Amplifier (lower) chassis (Figure 1-6) contains the following assemblies: a. Two 100 W solid state amplifiers b. Two half-octave filter boards for harmonic suppression c. Current limiting relay d. Two axial fans 111. The outer moulded case, and its removeable front and rear covers, protect the main and power chassis during operation, transit and storage. As well as containing chassis mounting hardware and miscellaneous fittings, the case houses a 28 VDC power supply unit, two high volume axial fans, a power and signal distribution panel and main on/off switch, a battery charging controller, and an RFI filter (Figure 1-7). SECTION 1 GENERAL SYSTEM DESCRIPTION 1-7 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 1-5: Main Chassis of the Digisonde 4D Figure 1-6: Power Amplifier Chassis of the Digisonde 4D 1-8 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 1-7: Sounder Transceiver Sub-system (Rear View) 112. A color monitor and keyboard are provided for installation, maintenance and testing purposes but are not required for remote operation. The GPS receiver is mounted externally to the sounder site building SPECIFICATIONS 113. Table 1-1 provides Digisonde 4D specifications. Table 1-1: Digisonde 4D specifications Quad Receiver Frequency Range Bandwidth Input Impedance Noise Figure Receiver Sensitivity Dynamic Range Recovery Time Output RF Output 0.5 – 30 MHz (all modes of operation) 34 kHz @ 3 dB (for 5 km range resolution) 50 Ω 11 dB (at receiver antenna preamplifier) -130 dBm (+/-6 dB) into main chassis; better at preamplifier (amount depending on preamp gain setting) >90 dB instantaneous >140 dB total operating range including gain control 40 μs 16-bit quadrature samples SECTION 1 GENERAL SYSTEM DESCRIPTION 1-9 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Frequency Scan Restriction of Transmission Ionogram Scan Time Frequency Synthesis Pulse Repetition Rate Pulse Width Peak Pulse Power Output Impedance Transmitter Type Lightning Protection User Interface Unattended operation Remote access & control Time Setting Built-in-Test (BIT) Self Calibration Signal Processing Processors # of Range Bins Height Range Height Resolution RF Interference Mitigation Waveform Processing Doppler Processing Doppler Range Doppler Resolution Amplitude Resolution Wave Polarization Standard Operating Modes 0.5 - 30 MHz, start, stop and step size selectable to 1 kHz Programmable list of frequencies Standard VIS ionogram 10 - 200 sec (varies with programmable settings) Fully digital (frequency switching time < 1μs) 100 and 200 pps 533μs (16 chips of 33 μs) waveform with 30 kHz signal bandwidth 2 channels @ 150 W each 50 Ω Dual RF MOSFET Amplifiers for polarized transmission using turnstile transmit antenna In-line spark gap discharge devices Controlled by 255 measurement programs, 255 schedules, automatic schedule switch rules and preprogrammed campaign events Network or Serial Port interface for Input/Output access to schedules, measurement data, diagnostic data, and operating software. (Internet, LAN, or Modem) Integrated GPS receiver keeps time to +/-25μs Full diagnostics to isolate failures to line replaceable units runs automatically, remotely accessible Built-in internal cal automatically updates phase/ amplitude adjustment tables. Remotely accessible results. Two Embedded Intel Dual Core processor SBCs (Control and Data platforms) Selectable: 256 or 512 0-1200 km (0 km used for self-calibration) 2.5 km sample spacing 500 m using differential phase technique RFIM reduces coherent interference up to 35 dB Pulse compression of 16-chip phase code provides 15 dB signal processing gain 4 to 128 integrations can provide up to 21 dB signal processing gain +/-3 Hz to +/-50 Hz .0125 to 12.5 Hz < 0.01 dB Alternating transmission with O and X, synchronized receive antenna polarizations (doubles reliability of O/X identification by ARTIST). Linear polarization on request. Linear Frequency Scan for Ionogram Multiplexed Frequency scan (finer Doppler resolution) Multi Fixed-Frequency (for TID and absorption studies) Plasma Drift & Ionospheric Tilt (direction and velocities) Synthesized multi-beam reception (detects off-vertical echoes) 1-10 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Precision Group Height (0.5 km h’ accuracy) HF surveillance mode Software (included with system) System Software Windows XP Embedded and RTEMS WEB Server for Real-time Data Apache, with access to real-time displays of ionogram, directogram, Monitoring skymap, drift velocity data and BIT Operating Software DESC (Control platform). DCART, Dispatcher, ARTIST with NHPC, DDA (Data platform). Online Ionogram Scaling Automatic Real Time Ionogram Scaling with True Height Analysis (ARTIST) vs 5.0.2 Online Drift Data Processing DDA (Drift Data Analysis) software, skymap generation, drift veloc- ity analysis, and calculation of ionospheric tilt Online Data Delivery FTP to multiple destinations 4 Receiver Antennas Antenna Type Active Crossed loops – Turnstile antennas (1.5m diameter) Antenna Array 4 antennas in 60 m triangle with central antenna Construction Schedule 80 PVC, with wire braid loop elements Electronics Preamplifier (powered via RF cable) with electronically switched po- larization. Pre-Amplifier Sensitivity -123 dBm (in 34k Hz bandwidth, not including signal processing) Specifications for Transmitter Antenna Antenna Type Turnstile Delta or Rhombic (2 orthogonal radiating elements) Tower 30 m or larger recommended Data Post-Analysis Workstation Computer Hardware Intel Dual Core processor, 19” LCD monitor, DVD R/W, Color Printer Computer Software Windows XP Ionogram Editing and Profile SAO Explorer 3.4 with NHPC electron density profile inversion tool, Inversion International Reference Ionosphere model, and access to the UML DIDBase data repository Drift Data Analysis Drift Explorer 1.2 with access to UML Drift-DB data repository SECTION 1 GENERAL SYSTEM DESCRIPTION 1-11 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL CHAPTER 2 METHODOLOGY, THEORETICAL BASIS AND IMPLEMENTATION BACKGROUND: IONOSPHERIC PROPAGATION OF RADIO WAVES 114. An ionospheric sounder uses basic radar techniques to detect the electron density (equal to the ion density since the bulk plasma is neutral) of ionospheric plasma as a function of height. The ionospheric plasma is created by energy from the sun transferred by particles in the solar wind as well as direct radiation (especially ultra-violet and x-rays). Each component of the solar emissions tends to be deposited at a particular altitude or range of altitudes and therefore creates a horizontally stratified medium where each layer has a peak density and to some degree, a definable width, or profile. The shape of the ionized layer is often referred to as a Chapman function [Davies, 1989] which is a roughly parabolic shape somewhat elongated on the top side. The peaks of these layers usually form between 70 and 300 km altitude and are identified by the letters D, E, F1 and F2, in order of their altitude. 115. By scanning the transmitted frequency from 1 MHz to as high as 40 MHz and measuring the time delay of any echoes (i.e., apparent or virtual height of the reflecting medium) a vertically transmitting sounder can provide a profile of electron density vs. height. This is possible because the relative refractive index of the ionospheric plasma is dependent on the density of the free electrons (Ne), as shown in Equation 1-1 (neglecting the geomagnetic field): 2(h) = 1 – k (Ne/f2) where k = 80.5, Ne is electrons/m3, and f is in Hz [Davies, 1989; Chen, 1987]. (1–1) 116. The behavior of the plasma changes significantly in the presence of the Earth’s magnetic field. An exhaustive derivation of m [Davies, 1989] results in the Appleton Equation for the refractive index, which is one of the fundamental equations used in the field of ionospheric propagation. This equation clearly shows that there are two values for refractive index, resulting in the splitting of a linearly polarized wave incident upon the ionosphere, into two components, known as the ordinary and extraordinary waves. These propagate with a different wave velocity and therefore appear as two distinct echoes. They also exhibit two distinct polarizations, approximately right hand circular and left hand circular, which aid in distinguishing the two waves. 117. When the transmitted frequency is sufficient to drive the plasma at its resonant frequency there is a total internal reflection. The plasma resonance frequency (fp) is defined by several constants, e – the charge of an electron, m – the mass of an electron, εo – the permittivity of free space, but only one variable, Ne – electron density in electrons/m3 [Chen, 1987]: fp2 = (Ne e2/4om) = kNe (1–2) A typical number for the F-region (200 to 400 km altitude) is 1012 electrons/m3, so the plasma resonance fre- quency would be 9 MHz. The value of  in Equation 1–1 approaches 0 as the operating frequency, f, ap- proaches the plasma frequency. The group velocity of a propagating wave is proportional to  so  = 0 implies 1-12 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL that the wave slows down to zero which is obviously required at some point in the process of reflection since the propagation velocity reverses. 118. The total internal reflection from the ionosphere is similar to reflection of radio frequency (RF) energy from a metal surface in that the re-radiation of the incident energy is caused by the free electrons in the medium. In both cases the wave penetrates to some depth. In a plasma the skin depth (the depth into the medium at which the electric field is 36.8% of its incident amplitude) is defined by:  0 2  fp f 2 1 (1–6) where 0 is the free space wavelength. 119. The major difference between ionospheric reflection and reflection from a metallic surface is that the latter has a uniform electron density while the ionospheric density increases roughly parabolically with altitude, with densities starting at essentially zero at stratospheric altitudes and rising to a peak at about 200 to 400 km. In the case of a metal there is no region where the wave propagates below the resonance frequency, while in the ionosphere the refractive index and therefore the wave velocity change with altitude until the plasma resonance frequency is reached. Of course if the RF frequency is above the maximum plasma resonance frequency the wave is never reflected and can penetrate the ionosphere and propagate into outer space. Otherwise what happens on a microscopic scale at the surface of a metal and on a macroscopic scale at the plasma resonance in the ionosphere is very similar in that energy is re-radiated by electrons which are responding to the incident electric field. MOTIVATION FOR A SMALL FLEXIBLE IONOSPHERIC SOUNDER 120. Current applications of ionospheric sounders fall into two categories: a. Support of operational systems, including shortwave radio communications and OTH radar systems. This support can be in the form of predictions of propagating frequencies at given times and locations in the future (e.g., over the ensuing month) or the provision of real-time updates (updated as frequently as every 15 minutes) to detect current conditions such that system operating parameters can be optimized. b. Scientific research to enable better prediction of ionospheric conditions and to understand the plasma physics of the solar-terrestrial interaction of the Earth’s atmosphere and magnetic field with the solar wind. 121. There has been considerable effort in producing global models of ionospheric densities, temperature, chemical constitution, etc, such that a few sounder measurements could calibrate the models and improve the reliability of global predictions. It has been shown that if measurements are made within a few hundred kilometers of each other, the correlation of the measured parameters is very high [Rush, 1978]. Therefore a network of sounders spaced by less than 500 km can provide reliable estimates of the ionosphere over a 250 km radius around them. 122. The areas of research pursued by users of the more sophisticated features of the Digisonde™ sounders include polar cap plasma drift, auroral phenomena, equatorial spread-F and plasma irregularity phenomena, and sporadic E-layer composition [Buchau et al., 1985; Reinisch 1987; and Buchau and Reinisch 1991]. There may be some driving technological needs (e.g., commercial or military uses) in some of these efforts, but many are simply basic research efforts aimed at better understanding the manifestations of plasma physics provided by nature. SECTION 1 GENERAL SYSTEM DESCRIPTION 1-13 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 123. The accurate measurement of all of the parameters, except frequency (it being precisely set by the system and need not be measured) depends heavily on the signal to noise ratio of the received signal. Therefore vertical incidence ionospheric sounders capable of acquiring high quality scientific data have historically utilized powerful pulse transmitters in the 2 to 30 kW range. The necessity for an extremely good signal to noise ratio is demanded by the sensitivity of the phase measurements to the random noise component added to the signal level. For instance, to measure phase to 1 degree accuracy requires a signal to noise ratio better than 40 dB (assuming a Gaussian noise distribution which is actually a best case), and measurement of amplitude to 10% accuracy requires over 20 dB signal to noise ratio. Of course, is it desirable that these measurements be immune to degradation from noise and interference and maintain their high quality over a large frequency band. This requires that at the lower end of the HF band the system’s design has to overcome absorption, noise and interference, and poor antenna performance and still provide at least a 20 to 40 dB signal to noise ratio. SIGNAL PROCESSING IN DIGISONDE 4D General Considerations 124. Several advances in ionospheric sounding were made over past four decades to move significantly beyond the basic pulse techniques developed in the 1930’s. Introduced techniques include:  Coherent integration of several pulses transmitted at the same frequency  Spectral pulse integration applicable to moving reflectors  Pulse compression for improved signal-to-noise ratio  Multiple receiver arrays  Transmission and reception of circularly polarized signals  Frequency multiplexing for improved Doppler resolution  Precision ranging on two closely separated frequencies  Mitigation of RF Interference  Pulse modulation for twin frequency sounding 125. Like its Digisonde predecessors, the Digisonde 4D simultaneously measures seven observable parameters of reflected (or in oblique incidence, refracted) signals received from the ionosphere: 1) Frequency 2) Range (or height for vertical incidence measurements) 3) Amplitude 4) Phase 5) Doppler Shift and Spread 6) Angle of Arrival 7) Wave Polarization 126. Because the physical parameters of the ionospheric plasma affect the way radio waves reflect from or pass through the ionosphere, it is possible by measuring all of these observable parameters at a number of discrete heights and discrete frequencies to map out and characterize the structure of the plasma in the ionosphere. Both the height and frequency dimensions of this measurement require hundreds of individual measurements to approximate the underlying continuous functions. The resulting measurement is called an ionogram and comprises a seven dimensional measurement of signal amplitude vs. frequency and vs. height as shown in Figure 1-8. 1-14 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 1-8: Six-Dimensional Ionogram 127. Figure 1-8 is a six-dimensional display, with sounding frequency as the abscissa, virtual reflection height (simple conversion of time delay to range assuming propagation at 3x108 m/sec) as the ordinate, signal amplitude as the dot size, and echo status (polarization, Doppler shift, and angle of arrival) mapped into 12 available distinct colors. The wave polarizations are shown as two different color groups (the green scale, “neutral” colors showing extraordinary polarization, the red scale, “demanding attention” colors showing ordinary polarization. The angle of arrival is shown by different colors (using the “warm” scale for South and the “cold” scale for North), and the Doppler shift is indicated by the color shades. For comparison, the insert in Figure 1-8 shows a conventional, three-dimensional ionogram with the signal amplitude shown as intensity. The left side of Figure 1-8 shows a table of ionospheric characteristics scaled automatically by the ARTIST software. Coherent Pulse Integration in Time Domain 128. Historically, first improvement in sounding technique was the coherent integration of several pulses transmitted at the same frequency. Two signals are coherent if, having a phase and amplitude, they are able to be added together (e.g., one radar pulse echo received from a target added to the next pulse echo received from the same target, thousandths of a second later) in such a way that the sum may be zero (if the two signals are exactly out of phase with each other) or double the amplitude (if they are exactly in phase). Coherent integration of N signals can provide a factor of N improvement in power. This technique was first used in the Digisonde™ 128 [Bibl and Reinisch, 1975] and further expanded to the case of moving reflectors by employing Doppler integration as further discussed below in Paragraph 149 et seq. Coded Pulses to Facilitate Pulse Compression Radar Techniques SECTION 1 GENERAL SYSTEM DESCRIPTION 1-15 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 129. Another general technique to improve on the simple pulse sounder is to stretch out the pulse by a factor of N, thus increasing the duty cycle so the pulse contains more energy without requiring a higher power transmitter (power x time = energy). However, lengthening the pulse deteriorates its range resolution properties. To maintain the higher range resolution of the simple short pulse, the long pulse can be phase modulated with a code to enable the receiver to create a synthetic pulse with the original (i.e., that of the short pulse) range resolution. Bi-phase, or phase reversal modulation was implemented in a network of sounders operated by the U.S. Navy in the 1960’s using a 13-bit Barker Code. 130. The critical factor in the use of pulse compression waveforms for any radar type measurement is the correlation properties of the internal phase code. Phase codes proposed and experimented with included the Barker Code [Barker, 1953], Huffman Sequences [Huffman 1962], Convoluted Codes [Coll, 1961], Maximal Length Sequence Shift Register Codes (M-codes) [Sarwate and Pursley, 1980], or Golay’s Complementary Sequences [Golay, 1961], which have been implemented in the VHF mesospheric sounding radar at Ohio State University [Schmidt et al., 1979] and in the DPS. The internal phase code alternative has just recently become economically feasible with the availability of very fast microprocessor and signal processor IC’s. Barker Coded pulses have been implemented in several ionospheric sounders to date, but until the DPS was developed there have been no other successful implementations of Complementary Series phase codes in ionospheric sounders. 131. The Digisonde 4D is able to be miniaturized by lengthening the transmitted pulse beyond the pulse width required to achieve the desired range resolution where the radar range resolution is defined as, ΔR = c / 2β, where β is the system bandwidth, or (1–4) = cT / 2 for a simple rectangular pulse waveform, with T being the width of a rectangular pulse The longer pulse allows a small low voltage solid state amplifier to transmit an amount of energy equal to that transmitted by a high power pulse transmitter (energy = power x time, and power = V2/R) without having to provide components to handle the high voltages required for tens of kilowatt power levels. The time resolution of the short pulse is provided by intrapulse phase modulation using programmable phase codes (user selectable and firmware expandable), the Complementary Codes, and M-codes are standard. The use of a Complementary Code pulse compression technique is described in this chapter, which shows that at 300 W of transmitter power the expected measurement quality is the same as that of a conventional sounder of about 500 kW peak pulse power. 132. The transmitted spread spectrum signal s(t) is a biphase (180° phase reversal) modulated pulse. As illustrated in Figure 1-9, bi-phase modulation is a linear multiplication of the binary spreading code p(t) (a.k.a. a chipping sequence, where each code bit is a “chip”) with a carrier signal sin(2πf0t) or in complex form, exp[j2πf0t], to create a transmitted signal, s(t) = p(t)exp[j2πf0t] (1–5) 1-16 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE s(t) DIGISONDE 4D SYSTEM MANUAL s(t) RF p(t) Carrier Code Gen. VIS1-3 Figure 1-9: Generation of a Bi-phase Modulated Spread Spectrum Waveform NOTE Notation throughout this chapter will use s(t) as the transmitted signal, r(t) the received signal and p(t) as the chip sequence. Functions r1(t) and r2(t) will be developed to describe the signal after various stages of processing in the receiver. The term chip is used rather than bit because for spread spectrum communications many chips are required to transmit one bit of message information, so a distinct term had to be developed. Figure 1-10 on the following page depicts the modulation of a sinusoidal RF carrier signal by a binary code (notice that the code is a zero mean signal, i.e., centred around 0 volts amplitude). Since the mixer in Figure 1-9 can be thought of as a mathematical multiplier, the code creates a 180o ( radians) phase shift in the sinusoidal carrier whenever p(t) is negative, since –sin(t) = sin(t+). 133. The binary spreading code is identical to a stream of data bits except that it is designed such that it forms a pattern with uniquely desirable autocorrelation function characteristics as described later in this chapter. The 16-bit Complementary Code pair used in the Digisonde 4D is 1-1-0-1-1-1-1-0-0-1-1-1-0-1-0-0 modulated onto the odd-numbered pulses and 0-0-1-0-0-0-0-1-0-1-1-1-0-1-0-0 modulated onto the even-numbered pulses. This pattern of phase modulation chips is such that the frequency spectrum of such a signal (as shown inFigure 1-10) is uniformly spread over the signal bandwidth, thus the term “spread spectrum”. In fact, it is interesting to note that the frequency spectrum content of the spread spectrum signal used by the DPS and Digisonde 4D is identical to that of the higher peak power, simple short pulse used by the Digisonde™ 256, even though the physical pulse is 8 times longer. Since they have the same bandwidth, Equation 1–4 would suggest that they have the same range resolution. It will be shown later in this chapter, that the ability of the Digisonde™ 256 and the DPS to determine range (i.e., time delay), phase, Doppler shift and angle of arrival is also identical between the two systems, even though the transmitted waveforms appear to be vastly different. SECTION 1 GENERAL SYSTEM DESCRIPTION 1-17 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL PSK MODULATED MAXIMAL LENGTH CODE ON NORMALIZED CARRIER FREQUENCY AT 4 TIMES MODULATION RATE 40 10dB PER DIV VERTICAL SCALE 30 20 10 VIS1-4 0 0 2 4 6 8 Figure 1-10: Spectral Content of a Spread-Spectrum Waveform 134. Since the transmitted signal would obscure the detection of the much weaker echo in a monostatic system the transmitted pulse must be turned off before the first E-region echoes arrive at the receiver which, as shown in Figure 1-11, is about TE = 600 μsec after the beginning of the pulse. Also, since the receiver is saturated when the transmitter pulse comes on again, the pulse repetition frequency is limited by the longest time delay (listening interval) of interest, which is at least 5 msec, corresponding to reflections from 750 km altitude. To meet these constraints, a 533 μsec pulse made up of eight 66.67 μsec phase code chips (15 000 chips/sec) is selected which allows detection of ionospheric echoes starting at 80 km altitude. To avoid excessive range ambiguity, a highest pulse repetition frequency of 200 pps is chosen, which allows reception of the entire pulse from a virtual height of 670 km (the pulse itself is 80 km long) altitude before the next pulse is transmitted. This timing captures all but the highest multihop F-region echoes which are of little interest. Under conditions where higher unambiguous ranges, and therefore longer receiver listening intervals, are desired 100 pps or 50 pps can be selected under software control. 135. The key to the pulse compression technique lies in the selection of a spreading function, p(t), which possesses an autocorrelation function appropriate for the application. The ideal autocorrelation function for any remote sensing application is a Dirac delta function (or instantaneous impulse, (t) since this would provide perfect range accuracy and infinite resolution. However, since the Dirac delta function has infinite instantaneous power and infinite bandwidth, the engineering tradeoffs in the design of any remote sensing system mainly involve how far one can afford to deviate from this ideal (or how much one can afford to spend in more closely approximating this ideal) and still achieve the accuracy and resolution required. More to the point, for a discussion of a discrete time digital system such as the DPS, the ideal signal is a complex unit impulse function, with the phase of the impulse conveying the RF phase of the received signal. The many different pulse compression codes all represent some compromise in achieving this ideal, although each code has its own advantages, limitations, and trade-offs. 1-18 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE F2 525 km DIGISONDE 4D SYSTEM MANUAL E 90 km Tx Rx Not to scale Tg = 0 s Te = 600 s VIS1-5 Tf = 3.5 ms Figure 1-11: Natural Timing Limitations for Monostatic Vertical Incidence Sounding 136. The autocorrelation function as applied to code compression in the DPS is defined as: R(k)   p(n) p(n  k) n (1–6) Therefore the ideal as described above is R(k) = (k). 137. For ionospheric applications, the received spread-spectrum coded signal, r(t), may be a superposition of several multipath echoes (i.e., echoes which have traveled over various propagation paths between the transmitter and receiver) reflected at various ranges from various irregular features in the ionosphere. The algorithm used to perform the code compression operates on this received multipath signal, r(t), which is an attenuated and time delayed (possibly multiple time delays) replica of the transmitted signal s(t) (from Equation 1–5), which can be represented as: P r(t)   aist  i  or i 1 (1–7) P r(t)   ai pt  i exp j2f0t  i  i 1 where  shows that the P multipath signals sum linearly at the receive antenna, ai is the amplitude of the ith multipath component of the signal, and i is the propagation delay associated with multipath i. The carrier phase i of each multipath could be expressed in terms of the carrier frequency and the time delay i ; however, since the multiple carriers (from the various multipath components) cannot be resolved, while the delays in the SECTION 1 GENERAL SYSTEM DESCRIPTION 1-19 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL complex code modulation envelope can be, a separate term, i, is used. Next, when the carrier is stripped off of the signal, this RF phase term will be represented by a complex amplitude coefficient i rather than ai. 1 Volt/Div VIS1- 6 Time (0.2 msec/Div) Figure 1-12: Conversion to Baseband by Undersampling 138. By down-converting to a baseband signal (a digital technique is shown in Figure 1-12), the carrier signal can be stripped away, leaving only the superposed code envelopes delayed by P multiple propagation paths. Figure 1-12 presents one way to strip the carrier off a phase modulated signal. This is the screen display on a digital storage oscilloscope looking at the RF output from the DPS system operating at 3.5 MHz. Notice that the horizontal scan spans 2 msec, which if the oscilloscope was capable of presenting more than 14 000 resolvable points, would display 7 000 cycles of RF. The sample clock in the digital storage scope is not synchronized to the DPS, however, the digital sampling remains coherent with the RF for periods of several milliseconds. The analog signal is digitized at a rate such that each sample is made an integer number of cycles apart (i.e., at the same phase point) and therefore looks like a DC level until the phase modulation creates a sudden shift in the sampled phase point. Therefore the 180º phase reversals made on the RF carrier show up as DC level shifts, replicating the original modulating code exactly. The more hardware intensive method of quadrature demodulation with hardware components (mixers, power splitters and phase shifters) can be found in any communications systems textbook, such as [Peebles, 1979]. After removing the carrier, the modified r(t), now represented by r1(t) becomes: P r(t)  i pt  i  i 1 (1–8) where the carrier phase of each of the multipath components is now represented by a complex amplitude i which carries along the RF phase term, originally defined by i in Equation 1–7, for each multipath. Since the 1-20 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL pulse compression is a linear process and contributes no phase shift, the real and imaginary (i.e., in-phase and quadrature) components of this signal can be pulse compressed independently by cross-correlating them with the known spreading code p(t). The complex components can be processed separately because the pulse compression (Equation 1–10) is linear and the code function, p(n), is all real. Therefore the phase of the crosscorrelation function will be the same as the phase of r1(t). 139. The classical derivation of matched filter theory [e.g., Thomas, 1964] creates a matched filter by first reversing the time axis of the function p(t) to create a matched filter impulse response h(t) = p(–t). Implementing the pulse compression as a linear system block (i.e., a “black box” with impulse response h(t)) will again reverse the time axis of the impulse response function by convolving h(t) with the input signal. If neither reversal is performed (they effectively cancel each other) the process may be considered to be a cross-correlation of the received signal, r(t) with the known code function, p(t). Either way, the received signal, r2(n) after matched filter processing becomes: r2(n) = r1(n) * h(n) = r1(n) * p(–n) (1–9) or by substituting Equation 1–8 and writing out the discrete convolution, we obtain the cross-correlation approach, P M P r2 (n)  i  pk  i pk  n   Mi n  i  i1 k 1 i1 (1–10) where n is the time domain index (as in the sample number, n, which occurs at time t = nT where T is the sampling interval), P is the number of multipaths, k is the auxiliary index used to perform the convolution, and M is the number of phase code chips. The last expression in Equation 1–10, the (n), is only true if the autocorrelation function of the selected code, p(t), is an ideal unit impulse or “thumbtack” function (i.e., it has a value of M at correlation lag zero, while it has a value of zero for all other correlation lags). So, if the selected code has this property, then the function r2(n), in Equation 1–9 is the impulse response of the propagation path, which has a value αi, (the complex amplitude of multipath signal i) at each time n = i (the propagation delay attributable to multipath i). 140. Figure 1-13 illustrates the unique implementation of Equation 1–10 employed for compression of Complementary Sequence waveforms. A 4-bit code is used in this figure for ease of illustration but arbitrarily long sequences can be synthesized (the DPS’s Complementary Code is 8-chips long). It is necessary to transmit two encoded pulses sequentially, since the Complementary Codes exist in pairs, and only the pairs together have the desired autocorrelation properties. Equation 1–8 (the received signal without its sinusoidal carrier) is represented by the input signal shown in the upper left of Figure 1-13. The time delay shifts (indexed by n in Equation 1–10 are illustrated by shifting the input signal by one sample period at a time into the matched filter. The convolution shifts (indexed by k in Equation 1–10 sequence through a multiply-and-accumulate operation with the four  1 tap coefficients. The accumulated value becomes the output function r2(n) for the current value of n. The two resulting expressions for Equation 1–10 (an r2(n) expression for each of the two Complementary Codes) are shown on the right with the amplitude M=4 clearly expressed. The non-ideal approxima- tion of a delta function, (n-τi), is apparent from the spurious a and –a amplitudes. However, by summing the two r2(n) expressions resulting from the two Complementary Codes, the spurious terms are cancelled, leaving a perfect delta function of amplitude 2M. SECTION 1 GENERAL SYSTEM DESCRIPTION 1-21 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Odd #'d Pulses — — –a a –a –a — — Even #'d Pulses — — a a a –a — — Code 1 Matched Filter —————— — –1 1–1 –1— Code 2 Matched Filter —————— — 1 1 1 –1— — a — –a 4a –a — a — + — –a — a 4a a — –a — r2 =  s[k-n] h[k] = — — — —8a — — — — y1 =  a p1[k-n] p1[k] VIS1-7 y2 =  a p2[k-n] p2[k] r2 = y1 + y2 Figure 1-13: Illustration of Complementary Code Pulse Compression 141. The amplitude coefficient M in Equation 1–10 is tremendously significant! It is what makes spreadspectrum techniques practical and useful. The M means that a signal received at a level of 1 μV would result in a compressed pulse of amplitude M μV, a gain of 20·log10(M) dB. Unfortunately, the benefits of all of that gain are not actually realized because the RMS amplitude of the random noise (which is incoherently summed by Equation 1–10) which is received with the signal goes up by a factor of \/M. However, this still represents a power gain (since power = amplitude2) equal to M, or 10·log10(M) dB. The \/M coefficient for the incoherent summation of multiple independent noise samples is developed more thoroughly in the following section on Coherent Spectral Integration, but the factor of M-increase for the coherent summation of the signal is clearly illustrated in Figure 1-13. 142. The next concern is that the pulse compression process is still valid when multiple signals are superimposed on each other as occurs when multipath echoes are received. It seems likely that multiple overlapping signals would be resolved since Equation 1–9 and the free space propagation phenomenon are linear processes, so the output of the process for multiple inputs should be the same as the sum of the outputs for each input signal treated independently. This linearity property is illustrated in Figure 1-14. Two 4-chip input signals, one three times the amplitude of the other, are overlapped by two chips at the upper left of the illustration. After pulse compression, as seen in the lower right, the two resolved components, still display a 3:1 amplitude ratio and are separated by two chip periods. 1-22 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE Odd #'d Pulses — –1 1 –4 2 –3 –3 — Even #'d Pulses — 1 1 4 2 3 –3 — Code 1 Matched Filter —————— — –1 1 –1 –1— Code 2 Matched Filter —————— — 1 1 1 –1— DIGISONDE 4D SYSTEM MANUAL — 1— 2 4 –4 12 –2— 3— + —–1—–2 4 4 12 2—–3— = — —— —8 —24 — —— — VIS1-8 Figure 1-14: Resolution of Overlapping Complementary Coded Pulses 143. The phase of the received signal is detected by quadrature sampling; but, how is the complex quantity, αi, or ai·exp[i], related to the RF phase (i) of each individual multipath component? It can be shown that this phase represents the phase of the original RF signal components exactly. As shown in Equations 1–11 and 1– 12, the down-converting (frequency translation) of r(t) by an oscillator, exp[j2πf0t] results in:   r1(t)  P ai p(t  i ) exp j2f0t  ji exp j2f0t  P ai p(t  i ) exp ji  i0 i0 or (1–11) P  r1(t)  i p(t  i ) , i0 where i  ai exp ji  is a complex amplitude (1–12) This signal maintains the parameter i which is the original phase of each RF multipath component. Note that the oscillator is defined as having zero phase (exp[j2f0t]). 144. Due to many possible mechanisms the pulse compression process will have imperfections, which may cause energy reflected from any given height to leak or spill into other heights to some degree. This leakage is the result of channel induced Doppler, mathematical imperfection of the phase code (except in the Complementary Codes which are mathematically perfect) and/or imperfection in the phase and amplitude response of the transmitter or receiver. Several codes were simulated and analyzed for leakage from one height to another and for tolerance to signal distortion caused by band-limiting filters. All of the pulse compression algorithms used are cross-correlations of the received signal with a replica of the unit amplitude code known to have been sent. Therefore, since Equation 1–10 represents a “cross-correlation” (the unit amplitude function p(t) is crosscorrelated with the complex amplitude weighted version) of p(k) with itself, it is the leakage properties of the autocorrelation functions which are of interest. 145. The autocorrelation function of the Complementary phase code is shown in Figure 1-15. SECTION 1 GENERAL SYSTEM DESCRIPTION 1-23 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 0.1 0.05 0 VIS1-9 1 2 3 TIME ( msecs ) Figure 1-15: Autocorrelation Function of the Complementary Series 146. Since the Complementary Series pairs do not leak energy into any other height bin this phase code scheme seemed optimum and was chosen for the Digisonde 4D vertical incidence measurement mode in order to provide the maximum possible dynamic range in the measurement. If there is too much leakage (for instance at a –20 dB level) then stronger echoes would create a “leakage noise floor” in which weaker echoes could not be detectable. 147. Even though the Complementary Code pairs are theoretically perfect, the physical realization of this signal may not be perfect. The Complementary Code pairs achieve zero leakage by producing two compressed pulses (one from each of the two codes) which have the same absolute amplitude spurious correlation peaks (or leakage) at each height, but all except the main correlation peak are inverted in phase between the two codes. Therefore, simply by adding the two pulse compression outputs, the leakage components disappear. Since the technique relies on the phase distance of the propagation path remaining constant between the sequential transmission of the two coded pulses, the phase change vs. time caused by any movement in the channel geometry (i.e., Doppler shift imposed on the signal) can cause imperfect cancellation of the two complex amplitude height profile records. Therefore, the Complementary Code is particularly sensitive to Doppler shifts since channel induced phase changes which occur between pulses will cause the two pulse compressions to cancel imperfectly, while with most other codes we are only concerned with channel induced phase changes within the duration of one pulse. However, if given the parameters of the propagation environment, we can calculate the maximum probable Doppler shift, and determine if this yields acceptable results for vertical incidence sounding. 148. With 200 pps, the time interval between one pulse and the next is 5 msec. If one pulse is phase modulated with the first of the Complementary Codes, while the next pulse has the second phase code, the interval over which motions on the channel can cause phase changes is only 5 msec. The degradation in leakage cancellation is not significant (i.e., less than –15 dB) until the phase has changed by about 10 degrees between the two pulses. The Doppler induced phase shift is: 1-24 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL f = 2TfD radians (1–13) where fD is the Doppler shift in Hz and T is the time between pulses. The Doppler shift can be calculated as: fD = (f0vr)/c (or for a 2-way radar propagation path) fD = (2f0vr)/c (1–14) where f0 is the operating frequency and vr is the radial velocity of the reflecting surface toward or away from the sounder transceiver. The radial velocity is defined as the projection of the velocity of motion (v) on the unit amplitude radial vector (r) between the radar location and the moving object or surface, which in the ionosphere is an isodensity surface. This is the scalar product of the two vectors: vr = v . r = |v| cos() (1–15) A phase change of 10 in 5 msec would require a Doppler shift of about 5.5 Hz, or 160 m/sec radial velocity (roughly half the speed of sound), which seldom occurs in the ionospheric except in the polar cap region. The 8-chip complementary phase code pulse compression and coherent summation of the two echo profiles provides a 16-fold increase in signal amplitude, and a 4-fold increase in noise amplitude for a net signal processing gain of 12 dB. The Doppler integration, as described later can provide another 21 dB of SNR enhancement, for a total signal processing gain of 42 dB, as shown by the following discussion. Coherent Spectral Integration 149. In ionospheric sounding, the motion of the ionosphere often makes it impossible to integrate by simple coherent summation for longer that a fraction of a second, although it is not rare to receive coherent echoes for tens of seconds. However, with the application of spectral integration (which is a byproduct of the Fourier transform used to create a Doppler spectrum) it is possible to coherently integrate pulse echoes for tens of seconds under nearly all ionospheric conditions [Bibl and Reinisch, 1978]. The integration may progress for as long a time as the rate of change of phase remains constant (i.e., there is a constant Doppler shift, Δf). The Digisonde™ 128PS, and all subsequent versions perform this spectral integration. 150. The pulse compression described above occurs with each pulse transmitted, so the 12 SNR improvement for 8-bit complementary phase codes is achieved without even sending another pulse. However, if the measurement can be repeated phase coherently, the multiple returns can be coherently integrated to achieve an even more detectable or “cleaner” signal. This process is essentially the same as averaging, but since complex signals are used, signals of the same phase are required if the summation is going to increase the signal amplitude. If the phase changes by more than 90 during the coherent integration then continued summation will start to decrease the integrated amplitude rather than increase it. However, if transmitted pulses are being reflected from a stationary object at a fixed distance, and the frequency and phase of the transmitted pulses remain the same, then the phase and amplitude of the received echoes will stay the same indefinitely. 151. The coherent summation of N echo signals causes the signal amplitude, to increase by N, while the incoherent summation of the noise amplitude in the signal results in an increase in the noise amplitude of only \/N. Therefore with each N pulses integrated, the SNR increases by a factor of \/N in amplitude which is a factor of N in power. This improvement is called signal processing gain and can be defined best in decibels (to avoid the confusion of whether it is an amplitude ratio or a power ratio) as: Processing Gain  20 S p Qp Si Qi (1–16) SECTION 1 GENERAL SYSTEM DESCRIPTION 1-25 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL where Si is the input signal amplitude, Qi the input noise amplitude, Sp the processed signal amplitude, and Qp the processed noise amplitude. Q is chosen for the random variable to represent the noise amplitude, since N would be confusing in this discussion. This coherent summation is similar to the pulse compression processing described in the preceding section, where N, the number of pulses integrated is replaced by M, the number of code chips integrated. 152. Another perspective on this process is achieved if the signal is normalized during integration, as is often done in an FFT algorithm to avoid numeric overflow. In this case Sp is nearly equal to Si, but the noise amplitude has been averaged. Thus by invoking the central limit theorem [Freund, 1967 or any basic text on probability], we would expect that as long as the input noise is a zero mean (i.e., no DC offset) Gaussian process, the averaged RMS noise amplitude, np (p for processed) will approach zero as the integration progresses, such that after N repetitions: np2 = ni2 / N (the variance represents power) (1–17) 153. Since the SNR can be improved by a variable factor of N, one would think, we could use arbitrarily weak transmitters for almost any remote sensing task and just continue integrating until the desired signal to noise ratio (SNR) is achieved. In practical applications the integration time limit occurs when the signal undergoes (or may undergo, in a statistical sense) a phase change of 90. However, if the signal is changing phase linearly with time (i.e., has a frequency shift, ), the integration time may be extended by Doppler integration (also known as, spectral integration, Fourier integration, or frequency domain integration). Since the Fourier transform applies the whole range of possible phase shifts needed to keep the phase of a frequency shifted signal constant, a coherent summation of successive samples is achieved even though the phase of the signal is changing. The unity amplitude phase shift factor, e–jt, in the Fourier Integral (shown as Equation 1–18) varies the phase of the signal r(t) as a function of time during integration. At the frequency () which stabilizes the phase of the component of r(t) with frequency  over the interval of integration (i.e., makes r(t) e–jt coherent) the value of the integral increases with time rather than averaging to zero, thus creating an amplitude peak in the Doppler spectrum at the Doppler line which corresponds to :  Fr(t)  R()  r(t)e jtdt (1–18) 154. Does this imply that an arbitrarily small transmitter can be used for any remote sensing application, since we can just integrate long enough to clearly see the echo signal? To some extent this is true. There is no violation of conservation of energy in this concept since the measurement simply takes longer at a lower power; however, in most real world applications, the medium or environment will change or the reflecting surface will move such that a discontinuous phase change will occur. Therefore a system must be able to detect the received signal before a significant movement (e.g., a quarter to a half of a wavelength) has taken place. This limits the practical length of integration that will be effective. 155. The discrete time (sampled data) processing looks very similar (as shown in Equation 1–19). For a signal with a constant frequency offset (i.e., phase is changing linearly with time) the integration time can be extended very significantly, by applying unity amplitude complex coefficients before the coherent summation is performed. This stabilizes the phase of a signal which would otherwise drift constantly in phase in one direction or the other (a positive or negative frequency shift), by adding or subtracting increasingly larger phase angles from the signal as time progresses. Then when the phase shifted complex signal vectors are added, they will be in phase as long as that set of “stabilizing” coefficients progress negatively in phase at the same rate as the signal vector is progressing positively. The Fourier transform coefficients serve this purpose since they are unity amplitude complex exponentials (or phasors), whose only function is to shift the phase of the signal, r(n), being analyzed. 1-26 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 156. Since the Digisonde™ sounders have always done this spectral integration digitally, the following presentation will cover only discrete time (sampled data rather than continuous signal notation) Fourier analysis.   N  jnk 2 F r(t)  R(k)  r[n]e NT n0 (1–19) where r[n] is the sampled data record of the received signal at one certain range bin, n is the pulse number upon which the sample r[n] was taken, T is the time period between pulses, N is the number of pulses integrated (number of samples r[n] taken), and k is the Doppler bin number or frequency index. Since a Doppler spec- trum is computed for each range sampled, we can think of the Fourier transforms as F56[] or F192[] where the subscripts signify with which range bin the resulting Doppler spectra are associated. 157. By processing every range bin first by pulse compression (12 dB of signal processing gain) then by coherent integration, all echoes from each range have gained at least 21 dB of processing gain (depending on the length of integration) before any attempt is made to detect them. NOTE Further explanation of Equation 1–19 which can be gathered from any good reference on the Discrete Fourier Transformation, such as [Openheim & Schaefer, Prentice Hall, 1975], follows. The total integration time is NT, where T is the sampling period (in the Digisonde 4D, the time period between transmitted pulses). The frequency spacing between Doppler lines, i.e., the Doppler resolution, is 2/NT rads/sec (or 1/NT Hz) and the entire Doppler spectrum covers 2/T rad/sec (with complex input samples this is /T, but with real input samples the positive and negative halves of the spectra are mirror image replicas of each other, so only /T rad/sec are represented). 158. What is coherently integrated by the Fourier transformation in the Digisonde 4D (as in any pulseDoppler radar) is the time sequence of complex echo amplitudes received at the same range (or height) that is, at the same time delay after each pulse is transmitted. Figure 1-14 shows data layout with range or time delay vertically and pulse number (typically 32 to 128 pulses are transmitted) horizontally which hold the received samples as they are acquired. After each pulse is transmitted, one column is filled from the bottom up at regular sampling intervals, as the echoes from progressively higher heights are received (33.3 msec/5 km). These columns of samples are referred to as height profiles, which are not to be confused with electron density profiles, but rather mirror the radar terminology of a “slant range profile” (range becomes height for vertical incidence sounding) which is simply the time record of echoes resulting from a transmitted pulse. A height profile is simply a column of numeric samples which may or may not represent any reflected energy (i.e., they may contain only noise) . SECTION 1 GENERAL SYSTEM DESCRIPTION 1-27 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL ANTN 1 , FREQ 1, O POL - 64 K HEIGHT (KM) ANTN 1 , FREQ 1, X POL - 64 K HEIGHT (KM) TIME (MSEC) ANTN 2 , FREQ 1, O POL - 64 K HEIGHT (KM) TIME (MSEC) ANTN 2 , FREQ 1, X POL - 64 K HEIGHT (KM) TIME (MSEC) ANTN 3 , FREQ 1, O POL - 64 K HEIGHT (KM) TIME (MSEC) ANTN 3 , FREQ 1, X POL - 64 K HEIGHT (KM) TIME (MSEC) ANTN 4 , FREQ 1, O POL - 64 K HEIGHT (KM) TIME (MSEC) ANTN 4 , FREQ 1, X POL - 64 K HEIGHT (KM) TIME (MSEC) TIME (MSEC) VERY STRONG ECHO AMPLITUDES STRONG ECHO AMPLITUDES Figure 1-16: Eight Coherent Parallel Buffers for Simultaneous Integration of Spectra Complex Windowing Function 159. With T, the sampling period between subsequent samples of the same coherent process, i.e., the same hardware parameters) defined by the measurement program, the first element of the Discrete Fourier Transform (i.e., the amplitude of the DC component) will have a spectral width of 1/NT. This spectral resolution may be 1-28 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL so wide that all Doppler shifts received from the ionosphere fall into this one line. For instance, in the midlatitudes it is very rare to see Doppler shifts of more that 3 Hz, yet with a 50 Hz spectrum of 16 lines, the Doppler resolution is 6.25 Hz, so a 3 Hz Doppler shift would still appear to show “no movement”. For sounding, it would be much more interesting if instead of a DC Doppler line, a +3.25 Hz and a –3.25 Hz line were produced, such that even very fine Doppler shifts would indicate whether the motion was up or down. The DC line is a seemingly unalterable characteristic of the FFT method of computing the Discrete Fourier Transform, yet with a true DFT algorithm the Fourier transform coefficients can be chosen such that, the centre of the Doppler lines analyzed can be placed wherever the designer desires them to be. What was needed was a –½ Doppler line shift which would be correct for any value of N or T. 160. Because the end samples in the sampled time domain function are random, a tapering window had to be used to control the spurious response of the Doppler spectrum to below –40 dB (to keep the SNR high enough to not degrade the phase measurement beyond 1°). Therefore a Hanning function, H(n), which is a real function, was chosen and implemented early in the DPS development. The reader is referred to [Oppenheim and Schafer, 1975] for the definition and applications of the Hanning function. The solution to achieving the ½ Doppler line shift was to make the Hanning function amplitudes complex with a phase rotation of 180° during the entire time domain sampling period NT. The new complex Hanning weighting function is applied simply by performing complex rather than real multiplications. This implements a single-sideband frequency conversion of ½ Doppler line before the FFT is performed. In the following equation, each received multipath signal has only one spectral component (k = Di) such that it can be represented as, i exp[j2nDi]: P r(n) = { i exp[–j2(nDi)} |H(n)| exp[–j2(n/2NT)] i=1 P = |H(n)|  i exp[–j2(nDi + n/2NT)) i=1 (1–20) Multiplexing 161. When sending the next pulse, it need not be transmitted at the same frequency, or received on the same antenna with the same polarization. With the Digisonde 4D it is possible to “go off” and measure something else, then come back later and transmit the same frequency, antenna and polarization combination and fill the second column of the coherent integration buffer, as long as the data from each coherent measurement is not intermingled (all samples integrated together must be from the same coherent statistical process). In this way, several coherent processes can be integrated at the same time. Figure 1-14 shows eight coherent buffers, independently collecting the samples for two different polarizations and four antennas. This can be accomplished by transmitting one pulse for each combination of antenna and polarization while maintaining the same frequency setting (to also integrate a second frequency would require eight more buffers), in which case, each subsequent column in each array will be filled after each eight pulses are transmitted and received. This multiplexing continues until all of the buffers are filled with the desired number of pulse echo records. The DPS can keep track of 64 separate buffers, and each buffer may contain up to 32 768 complex samples. The term “pulse” is used generically here. For Complementary Coded waveforms a pulse actually requires two pulses to be sent. However, in both cases, after each pulse compression, one complex amplitude synthesized pulse, r2(n) in Equation 1–10 which is equivalent to a 67 sec rectangular pulse exists which can be placed into the coherent buffer. 162. The full buffers now contain a record of the complex amplitude received from each range sampled. Most of these ranges have no echo energy; only externally generated manmade and natural noise or interference from radio transmitters. If a particular ionospheric layer is providing an echo, each height profile will have SECTION 1 GENERAL SYSTEM DESCRIPTION 1-29 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL significant amplitude at the height corresponding to that layer. By Fourier transforming each row of the coherent buffer a Doppler spectrum describing the radial velocity of that layer will be produced. Notice that the sampling frequency at that layer is less than or equal to the pulse repetition frequency (on the order of 100 Hz). 163. After the sequence of N pulses is processed, the pulse compression and Doppler integration have resulted in a Doppler spectrum stored in memory on the DSP card for each range bin, each antenna, each polarization, and each frequency measured (maximum of 4 MILLION simultaneously integrated samples). The program now scans through each spectrum and selects the largest one amplitude per height. This amplitude is converted to a logarithmic magnitude (dB units) and placed into a new one-dimensional array representing a height profile containing only the maximum amplitude echoes. This technique of selecting the maximum Doppler amplitude at each height is called the modified maximum method, or MMM. If the MMM height profile array is plotted for each frequency step made, this results in an ionogram display, such as the one shown in Figure 1-17. Figure 1-17: VI Ionogram Consisting of Amplitudes of Maximum Doppler Lines Radio Frequency Interference Mitigation (RFIM) 164. Except for the FM/CW chirpsounder which operates well on transmitter power levels of 10 to 100 W (peak power) the above techniques and cited references typically employ a 2 to 30 kW peak power pulse trans- 1-30 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL mitter. This power is needed to get sufficient signal strength to overcome an atmospheric noise environment which is typically 20 to 50 dB (CCIR Noise Tables) above thermal noise (defined as kTB, the theoretical minimum noise due to thermal motion, where k = Boltzman’s constant, T = temperature in K, and B = system bandwidth in Hz). More importantly, however, since ionogram measurements require scanning of the entire propagating band of frequencies in the 0.5 to 20 MHz RF band (up to 45 MHz for oblique measurements), the sounder receiver will encounter broadcast stations, ground-to-air communications channels, HF radars, ship-toshore radio channels and several very active radio amateur bands which can add as much as 60 dB more background interference. Therefore, the sounder signal must be strong enough to be detectable in the presence of these large interfering signals. 165. To make matters worse, a pulse sounder signal must have a broad bandwidth to provide the capability to accurately measure the reflection height, therefore the receiver must have a wide bandwidth, which means more unwanted noise is received along with the signal. The noise is distributed quite evenly over bandwidth (i.e., white), while interfering signals occur almost randomly (except for predictably larger probabilities in the broadcast bands and amateur radio bands) over the bandwidth. Thus a wider-bandwidth receiver receives proportionally more uniformly distributed noise and the probability of receiving a strong interfering signal also goes up proportionally with increased bandwidth. 166. The 33 s wide chips of the DPS transmitter pulses imply a transmission bandwidth of 30 kHz requiring a receiver bandwidth of at least 30 kHz. This large bandwidth makes the receiver susceptible to a variety of “contaminating” radio emissions that are received together with the signal. Figure 1-18 illustrates the typical situation when a wideband signal is mixed with two types of radio contamination, wideband background noise and narrow-band interferers. Interferers Signal Noise Amplitude Frequency Figure 1-18: Wideband received signal spectrum contaminated by interferences and background noise. 167. Effective methods for mitigating the background noise exist such as signal integration/accumulation, inter-pulse phase switching, pulse modulation, or increased transmission power, but removing narrow-band interferers poses a significant challenge. Such interferers are typically signals from other transmitters, in many cases broadcasting stations, with unpredictable occurrences at a priori unknown frequencies. 168. To largely suppress these narrow-band interferers we implemented the digital RFIM technique, which is based on a patented technique developed by Bibl [2005]. This technique determines (a) the exact frequency SECTION 1 GENERAL SYSTEM DESCRIPTION 1-31 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL with sub-frequency spectral resolution of the largest contributor to the spectrum of the input signal, (b) amplitude and phase of the found contributor by using a single-line spectral analysis of the input signal at the determined frequency, and then (c) subtracts the interferer signal from the input signal in the time domain, and (d) repeats the algorithm for the next biggest interferer, etc. 169. Figure 1-19 illustrates the RFIM performance in a lab test configuration with a coherent interference signal infused at 20 dB above the loopback test signal. The upper panel in Figure 1-19 displays the Fourier spectrum of the digisonde signal (16-chip phase-coded pulse). The lower panel shows the spectrum of the same signal with the added interferer appearing as a spike near 16 kHz. Amplitude, dB 90 80 Signal spectrum 70 60 50 40 30 20 10 80 -30 -20 -10 0 10 Frequency, kHz 20 30 70 60 Signal+interferer spectrum Interferer 50 40 30 20 10 -30 -20 -10 0 10 20 30 Frequency, kHz Figure 1-19: Spectrum of the received signal without interferer (top) and with interferer (bottom). 170. The objective of the RFI mitigation algorithm is to remove the interferer signal before any further signal processing is done. To subtract this interference signal from the input signal requires knowledge of its exact frequency, phase, and amplitude. Figure 1-20 shows the spectrum of a truncated monochromatic wave. The width of the main spectral peak is inversely proportional to the length of the time period over which the spectrum is calculated. 1-32 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Amplitude, norm. 1.2 1.0 0.8 f = 32.3/T I A 0.6 0.4 B 0.2 0.0 20 22 24 26 28 30 32 34 36 38 40 m Figure 1-20: Spectrum of a truncated CW signal. 171. Conventional DFT algorithms calculate the spectral amplitudes of the integer-indexed frequencies that are multiples of 1/T where T is the coherent integration time. In general, the interferer frequency fI will not be a harmonic of 1/T, i.e., fI ≠ m/T (Figure 1-20). The frequency fI is given by fI  fA  1 T  A B  B , (1-21) where fA is the frequency of the stronger of the two strongest spectral components, and A and B are their amplitudes. We have experimentally verified that this algorithm works reliably. Once the precise frequency is known, a single-line discrete Fourier transformation determines the amplitude and phase of the interferer:  ~ CI  N 1  1 N n0 ~ Sn expi 2  fI n (1-22) where C I is the complex spectral amplitude, ~ Sn are the complex signal time samples, and N is the total number of sam- ples. The inverse transform of (2) gives the precise time domain presentation of the interferer ~ In ~  CI exp i 2 fI n, (1-23) This function can now simply be subtracted from the input data. The RFIM procedure steps are summarized in Table 3. Table 1-2: RFIM Procedure Steps Step # 1 2 3 4 5 6 Step description Calculate the DFT of the received signal. Find the strongest amplitude A in the spectrum. If the strongest spike does not qualify as a narrow-band interferer, stop. Determine the exact frequency of the interferer via Eq. (1) Do “single line spectral analysis” to determine the exact interferer amplitude and phase and perform the inverse Fourier transformation. Subtract the interferer signal from the received signal If the specified number of iterations is reached, stop. Otherwise, go to step 1 to determine next strongest interferer Angle of Arrival Measurement Techniques SECTION 1 GENERAL SYSTEM DESCRIPTION 1-33 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 172. Another new development in the 1970’s was the coherent multiple receiver array [Bibl and Reinisch, 1978] which allows angle of arrival (incidence angle) to be deduced from phase differences between antennas by standard interferometer techniques. Given a known operating frequency, and known antenna spacing, by measuring the phase or phase difference on a number of antennas, the angle of arrival of a plane wave can be deduced. This interferometry solution is invalid, however, if there are multiple sources contributing to the received signal (i.e., the received wave therefore does not have a planar phase front). This problem can be overcome in over 90% of the cases as was first shown with the Digisonde™ 256 [Reinisch et al., 1987] by first isolating or discriminating the multiple sources in range, then in the Doppler domain (i.e., isolating a plane wavefront) before applying the interferometry relationships.   l VIS1-16 Path difference  l = d sin Phase difference  =  d sin  Figure 1-21: Angle of Arrival Interferometry 173. The Digisonde 4D system uses two distinct techniques for determining the angle of arrival of signals received on the four antenna receiver array, a. An aperture resolution technique using digital beamforming, in which four antennas are used to form seven beams and then select the beam with the largest amplitude as the best representation of the echo arrival angle; and b. A super-resolution technique, in which signal phases in antenna triplet combinations are used to restore the angle direction to the reflecting source in the ionosphere. 174. Both techniques utilize the basic principle of interferometry, which is illustrated in Figure 1-21. This phenomenon is based on the free space path length difference between a distant source and each of some number of receiving antennas. The phase difference () between antennas is proportional to this free space path difference (l) based on the fraction of a wavelength represented by l. 1-34 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL l = d sin and  = (2pl)/ = (2 d sin)/ (1–23) where  is the zenith angle, d is the separation between antennas in the direction of the incident signal (i.e., in the same plane as  is measured), and  is the free space wavelength of the RF signal. This relationship is used to compute the phase shifts required to coherently combine the four antennas for signals arriving in a given beam direction, and this relationship (solved for ) is also the basis of determining angle of arrival directly from the independent phase measurements made on each antenna. 175. Figure 1-22 shows the physical layout of the four receiving antennas. The various separation distances of 17.3, 34.6, 30 and 60 m are repeated in six different azimuthal planes (i.e., there is six way symmetry in this array) and therefore, the ’s computed for one direction also apply to five other directions. This six-way symmetry is exploited by defining the six azimuthal beam directions along the six axes of symmetry of the array, making the beamforming computations very efficient. Section 2 of this manual contains detailed information for the installation of receive antenna arrays. Magnetic North #2 30 m 60 m 60 m 17.32 m #1 34.64 m #4 30 m 30  30 60 m VIS3-3 #3 Figure 1-22: Antenna Layout for 4-Element Receiver Antenna Array Digital Beamforming (aperture resolution technique) 176. Digital beamforming is done by taking four complex amplitudes observed in a particular Doppler line of the spectrum on four antennas and forming seven beams shown in Figure 1-23, one overhead (0° zenith an- SECTION 1 GENERAL SYSTEM DESCRIPTION 1-35 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL gle) and six oblique beams (the nominal 30° zenith angle can be changed by the operator) centred at North and South directions and each 60° in between. All seven beams are formed using the same four complex samples, at one reflection height at a time. Figure 1-23: Seven digitally synthesized beams for the angle of arrival measurement in ionogram mode 177. Oblique beams are formed by phase shifting the four complex amplitudes to compensate for the additional path length in the direction of each selected beam. If a signal has actually arrived from near the centre of one of the beams formed, then after the phase shifting, all four signals can be summed coherently, since they now have nearly the same phase, so that the beam amplitude of the sum is roughly four times each individual amplitude. The farther the true beam direction is away from a given beam centre the farther the phase of the four signals drift apart and the smaller the summed amplitude. However, in the DPS system the beams are so wide that even at the higher frequencies the signal azimuth may deviate more than 30° from the beam centres and the four amplitudes will still sum constructively [Murali, 1993]. 178. The technique for finding the angle of arrival is then simply to compare the amplitude of the signal on each beam and declare the direction as the beam centre of the strongest beam. The accuracy of this technique is limited to 30° in azimuth and 15° in elevation angle (the six azimuth beams are separated by 60° and the oblique beams are normally set 30° away from the vertical beam); as opposed to the Drift angle of arrival technique described in the next section which obtains accuracies approaching 1°. The fundamental principle of this technique is that there is no direction which can create a larger amplitude in a given beam than the direction of the centre of that beam. Therefore, detecting the direction by selecting the beam with the largest amplitude can never be an incorrect thing to do. One has to avoid thinking of the beam as excluding echoes from other directions and realize that all that is needed is that a beam favours echoes more as their angle of arrival becomes closer to the centre of that beam. In fact with a four element array the summed amplitude in a wrong direction 1-36 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL may be nearly as strong as it is in the correct beam, however, given that the same four complex amplitudes are used as input it cannot be stronger. 179. The phase shifts required to sum echoes into each of the seven beams depend on four variables: a. the signal wavelength, b. the antenna geometry (separation distance and orientation), c. the azimuth angle of arrival, and d. the zenith angle of arrival. The antenna weighting coefficients are unity amplitude with a phase which is the negative of the extra phase delay caused by the propagation delay, thereby removing the extra phase delay. The phase delays for antenna is resulting from arrival angle spherical coordinates (j, j) which corresponds to the direction of beam j, are described (using Equation 1–20) by the following: ij = (2 sinj / ) dij' (1–21) where ij is the phase difference between antenna i’s signal and antenna 1’s signal, j is the zenith angle (0 for overhead), and dij' is the projection of the antenna separation distance (from antenna i to antenna 1) upon the wave propagation direction. The parameter d' is dependent on the antenna positions which can be placed on a Cartesian coordinate system with the central antenna, antenna 1, at the origin and the X axis toward the North and the Y axis toward the West. With this definition the azimuth angle  is 0° for signals arriving from the North and: dij' = (xi cos j + yi sin j) (1–22) Since antenna 1 is defined as the origin, x1 and y1 are always zero, so i has to be zero. This makes antenna 1 the phase reference point which defines the phase of signals on the other antennas. The correction coefficients i are unit amplitude phase conjugates of the propagation induced phase delays: ij = 1.0  i(f,xi,yi,j,j) = 1–ij (1–23) Because they are frequency dependent, these correction factors must be computed at the beginning of each CIT when the beamforming mode of operation has been selected. A full description as well as some modeling and testing results were reported by [Murali, 1993]. 180. Although the received signal is resolved in range/height before beamforming, the beamforming technique is not dependent on isolating a signal source before performing the angle of arrival calculations. If two sources exist in a single Doppler line then these components (the amplitude of the Doppler line can be thought of as a linear superposition of the two signal components) then some of each of them will contribute to an enhanced amplitude in their corresponding beam direction. Conversely, the Drift technique assumes that the incident radio wave is a plane wave (thus requiring isolation of any multiple sources). Example A.: Given the antenna geometry shown in Figure 1-17, at an operating frequency of 4.33 MHz (l = 69.28 m), a beam in the eastward direction and 30 off vertical would, according to Equation 1–20, require a phase shift of 90 on antenna 4, –45 on antennas 2 and 3, and 0 on antenna 1. If an echo is re- SECTION 1 GENERAL SYSTEM DESCRIPTION 1-37 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL ceived from that direction it would be received on the four antennas as four complex amplitudes at the height corresponding to the height (or more precisely, the range, since there may be a horizontal component to this distance) of the reflecting source feature. Therefore, a single number per antenna can be analyzed by treating one echo height at a time, and by selecting only one (the maximum) complex Doppler line at that height and that antenna. Assume that the following four complex amplitudes have been receive on a DPS system at, for instance, a height of 250 km. This is represented (in polar notation) as: Antenna 1: 830 135 Antenna 2: 838 42 Antenna 3: 832 182 Antenna 4: 827 179 To these sampled values add the +90and –45 phase corrections mentioned above producing: Antenna 1: 830 135 or –586 + j586 Antenna 2: 838 132 or –561 + j623 Antenna 3: 832 137 or –608 + j567 Antenna 4: 827 134 or –574 + j594 East Beam (sum of above) = –2329+j2370 (3329134.5 in polar form) Since the sum is roughly four times the signal amplitude on each antenna there has been a coherent signal enhancement for this received echo because it arrived from the direction of the beam. It is interesting to note here, that these same four amplitudes could have been phase shifted corresponding to another beam direction in which case they would not add up in-phase. The DPS does this seven times at each height, using the same four samples, then detects which beam results in the greatest amplitude at that height. Of course at a different height another source may appear in a different beam, so the beamforming must be computed independently at each height. Drift Mode – Super-Resolution Direction Finding 181. By analyzing the spatial variation of phase across the receiver aperture, using Equation 1–20, the twodimensional angle of arrival (zenith angle and azimuth angle) of a plane wave can be determined precisely using only three antennas. The term super-resolution applies to the ability to resolve distinct closely spaced points when the physical dimensions (in this case, the 60 m length of one side of the triangular array) of the aperture used is insufficient to resolve them (from a geometric optics standpoint). Therefore, the use of interferometry provides super resolution. This is required for the Drift measurements because the beam resolution achievable with a 60 m aperture at 5 MHz is about 60, while 5 or better is required to measure plasma velocities accurately. Using beamforming to achieve a 5 angular resolution at 5 MHz would require an aperture dimension of 600 m, which would have to be filled with on the order of 100 receiving antenna elements. Therefore the Drift technique described here is a tremendous savings in system complexity. The Drift mode concept appears at first glance to be similar to the beamforming technique, but it is a fundamentally different process. 182. The Drift mode depends on a single echo source being isolated such that its phase is not contaminated by another echo (from a different direction but possibly arriving with the same time delay). This technique works amazingly well because at a given time, the overhead ionosphere tends to drift uniformly in the same direction with the same velocity. This means that each off-vertical echo will have a Doppler shift proportional 1-38 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL to the radial velocity of the reflecting plasma and to cos a where a is the angle between the position vector (radial vector from the observation site to the plasma structure) and velocity vector of the plasma structure, as presented in Equation 1–14. Therefore, for a uniform Drift velocity the sky can be segmented into narrow bands (e.g., 10’s of bands) based on the value of cos a which correspond to particular ranges of Doppler shifts [Reinisch et al, 1992]. These bands are shown in Figure 1-19 as the hyperbolic dashed lines [Scali, 1993] which indicate at what angle of arrival the Doppler line number should change if the whole sky is drifting at the one velocity just calculated by the DDA program. In other words, the agreement of the Doppler transitions with the boundaries specified by the uniform drift assumption is a test of the validity of the assumption for the particular data being analyzed. Figure 1-19 Radial Velocity Bands as Defined by Doppler Resolution 183. Both isolating the sources of different radial velocities and resolving echoes having different ranges (into 10 km height bins), results in very effective isolation of multiple sources into separate range/Doppler bins. If multiple sources exist at the same height they are usually resolved in the Doppler spectrum computed for that height, because of the sorting effect which the uniform motion has on the radial velocities. If the resolution is sufficient that a range/Doppler bin holds signal energy from only one source, the phase information in this Doppler line can be treated as a sample of the phase front of a plane wave. Even though many coherent echoes have been received from different points in the sky, the energy from these other points is not represented in the complex amplitude of the Doppler line being processed. This is important because the angle of arrival calculation is accomplished with standard interferometry (i.e., solving Equation 1–20 for ), which assumes no multiple wave interference (i.e., a perfect plane wave). SECTION 1 GENERAL SYSTEM DESCRIPTION 1-39 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 184. A fundamental distinction between the Drift mode and beamforming mode is that in the Drift mode the angle of arrival calculation is applied for each Doppler line in each spectrum at each height sampled, not just at the maximum amplitude Doppler line. A data dependent threshold is applied to try to avoid solving for locations represented by Doppler lines that contain only noise, but even with the threshold applied the resulting angle of arrival map may be filled with echo locations which result from echoes much weaker than the peak Doppler line amplitudes. In beamforming, only the echoes representing the dominant source at each height are stored on tape, therefore no other source echoes are recoverable from the recorded data. 185. It has been found that vertical velocities are roughly 1/10th the magnitude of horizontal velocities [Reinisch et al, 1991]. Since the horizontal velocities from echoes directly overhead result in zero radial velocity to the station, the Drift technique works best in a very rough, or non-uniform ionosphere, such as that found in the polar cap regions or the equatorial regions, because they provide many off-vertical echoes. 186. For a smooth spherically concentric (with the surface of the earth) ionosphere all the echoes will arrive from directly overhead and the resulting Drift skymaps will show a single source location at zenith angle = 0. For horizontal gradients or tilts within that spherically concentric uniform ionosphere however, the single source point would move in the direction of the N/N (N as in Equation 1–1) gradient (the local electron density gradient), one degree per degree of tilt, so the Drift measurement can provide a straightforward measurement of ionospheric tilt. 187. Resolution of source components by first isolating multiple echoes in range then in Doppler spread (velocity distribution) combined with interferometer principles is a powerful technique in determining the angle of arrival of superimposed multipath signals. Two Frequency Precision Ranging Mode 188. The phase of an echo from a target, or the phase of a signal after passing through a propagation medium is dependent on three things: 1. the absolute phase of the transmitted signal; 2. the transmitted frequency (or free space wavelength); and 3. the phase distance, d, where: D d =  (f,x,y,z) dl 0 (1–24) is the line integral over the propagation path, scaled by the refractive index if the medium is not free space. If the first two factors, the transmitted phase and frequency, can be controlled very precisely, then measuring the received phase at two different frequencies makes it possible to solve for the propagation distance with an accuracy proportional to the accuracy of the phase measurement, which in turn is proportional to the received SNR. This is often referred to as the d/df technique. The two measurements form a set of linear equations with two equations and two unknowns, the absolute transmitted phase and the phase distance. If there are several “propagation path distances” as is the case in a multipath environment, then measurement at several wavelengths can provide a measure of each separate distance. However, instead of using a large set of linear equations, the phase of the echoes have chosen to be analyzed as a function of frequency, which can be done very efficiently with a Fast Fourier Transform. The basic relations describing the phase of an echo signal are: (f) = –2fp = –2d/ = –2(f/c)d (1–25) 1-40 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL where d is the propagation path length in metres (the phase path described in Equation 1–24, f in Hz,  in radi- ans,  in metres and p is the propagation delay in seconds. Note that the first expression casts the propagation delay in terms of time delay (# of cycles of RF), the second in terms of distance (# of wavelengths of RF), and the third relates frequency and distance using c. 189. For monostatic radar measurements the distance, d is twice the range, R, so Equation 1–25 becomes: (f) = –4R/ = –4(f/c)R (1–26) If a series of N RF pulses is transmitted, each changed in frequency by f, one can measure the phases of the echoes received from a reflecting surface at range R. It is clear from Equation 1–26 that the received phase will change linearly with frequency at a rate directly determined by the magnitude of R. Using Equation 1–26 one can express the received phase from each pulse (indexed by i) in this stepped frequency pulse train: i (fi) = –4fip = –4fi(R/c) (1–27) where the transmitted frequency fi can be represented as: fi = f0 + if a start frequency plus some number of incremental steps. (1–28) 190. This measurement forms the basis of the DPS’s Precision Group Height mode. By making use of the simultaneous (multiplexed) operation at multiple frequencies (i.e., multiplexing or interlacing the frequency of operation during a coherent integration time (CIT) it is possible to measure the phases of echoes from a particular height at two different frequencies. If these frequencies are close enough that they are reflected at the same height then the phase difference between the two frequencies determines the height of the echo. 191. The following development of the two frequency ranging approach leads to a general theory (but not expoused here) covering FM/CW ranging and stepped frequency radar ranging. Using Equation 1–26 a two frequency measurement of  allows the direct computation of R, by: 2–1 = 4R(f1 – f2)/c = 4Rf/c (1–29) R = c(2 – 1)/4f (1–30) 192. It is easy to see from Equation 1–29 that if the range is such that RΔf/c is greater than 1/2 then the magnitude of 2-1 will exceed 2 which is usually not discernible in a phase measurement, and therefore causes an ambiguity. This ambiguity interval (D for distance) is R = DA = (1/2)c/f = c/2f (1–31) Example B.: The measured phase is (2 - 1) = /8 while f = 1 kHz, then R = 9.375 km. In the example above with f = 1 kHz, the ambiguous range DA is 150 km. Since a 0 km reflection height must certainly give the same phase for any two frequencies (i.e., 0), then given that the ambiguity interval is 150 km, then for this value of f, the phase difference must again be zero at 150, 300, 450 km etc, since 0 km is one of the equal phase points, and all other ranges giving a phase difference of 0 are spaced from it by 150 km. If the phase measurements 2 and 1 were taken after successive pulses at a time delay corresponding to a range of 160 km (at least one sample of the received echo must be made during each pulse width, i.e., at a rate equal to or greater than the system bandwidth, see Equation 1–4), one would conclude that there is an extra 2 in the phase difference SECTION 1 GENERAL SYSTEM DESCRIPTION 1-41 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL and that the true range is 159.375 km, not 9.375 km. Therefore, the measurement must be designed such that the raw range resolution of the transmitted pulse is sufficient to resolve the ambiguity in the d/df measurement. 193. The validity of the two-frequency precision ranging technique is lost if there is more than one source of reflection within the resolution of the radar pulse. The phase of the received pulse will be the complex vector sum of the multiple overlapping echoes, and therefore any phase changes (i) will be partially influenced by each of the multiple sources and will not correctly represent the range to any of them. Therefore, in the general propagation environment where there may be multiple echo sources (objects producing a reflection of RF energy back to the transmitter), or for multipath propagation to and from one or more sources, many frequency steps are needed to resolve the different components influencing fi. This “many step” approach can be performed in discrete frequency steps as in the DPS’s HRR mode, or by a continuous linear sweep, as done in a chirpsounder described in [Haines, 1994]. Passive RF Sensing Measurements 194. The concept of passive ionospheric RF sensing is to receive signals from remote transmitters of opportunity in order to infer characteristics of the ionospheric channel that received signals have traveled. Typical area of interest to passive RF measurements is imaging of small-scale ionospheric irregularities, especially if such observations can be made multi-static. Use of the digisondes in passive RF sensing has been constrained by the need to capture highly voluminous time-domain data for processing, until release of the Digisonde 4D model in 2007-2008 whose high bandwidth interfaces and modern embedded computers were adequate for the task. 195. In order to use the DPS system for the oblique sounding with signals from external transmitters of opportunity, there is an important problem to be solved. It concerns the inconsistency between the DPS effective sampling rate and the frequency bandwidth of the receive signals. To generate a valid digital presentation of the received broadcasting signal, the sampling rate must be at least twice the signal bandwidth. The maximum number of samples in the DPS spectrum is 128. With an integration time of 40 sec this results in a sampling rate of 3.2 Hz and an unambiguous spectral range of 1.6 Hz (considering the quadrature sampling). The signals of most broadcasting stations have a bandwidth of the order of 5 kHz [FCC regulations, 1998] as shown in Figure 1-24. Because of the low effective sampling rate and large receive bandwidth, the side modulation frequency (sideband) components would be “aliased”, or “folded” into the frequency band of the analysis and distort the measurements. If one were only to measure the Doppler frequency shift of the signal, this effect would not present a significant problem as long as the carrier frequency spectral line has an amplitude significantly larger than that of the sideband, which is usually the case (carrier frequency is at least 20 dB stronger than the sidebands). But signal angles of arrival are calculated from the phase measurements, and for these parameters the aliasing effect is a problem. This is because the phases of the sideband spectral components are random-like and fluctuate significantly during the coherent integration time. 1-42 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 1-24: Spectrum of the signal of broadcasting stations with 6 MHz carrier frequency. 196. To remove the aliasing effect, it is necessary to either increase the sampling rate, or decrease the receiver bandwidth by using a narrow-band filter, either analog or digital. Implementing a digital filter provides certain advantages, mainly the flexibility of the system, and requires no additional hardware parts. Such a filter was designed and implemented as a part of this work. 197. Figure 1-25 helps understanding the digital filtering algorithm. To simplify the picture only real samples of the digitized signal are drawn, and a single operating frequency is assumed. The top panel shows the digitizer samples for the 10 km height resolution. As shown, for each sounding pulse 512 samples are averaged and the resulting value is stored in the DSP memory as the first height sample (bottom panel). After this, the spectrum is calculated for the first height range only, just as in the regular DPS signal processing for the drift mode of operation. 198. The design of this narrow-band filter is just the realization of a finite impulse response (FIR) filter with decimation. The theory of such filters is documented in literature and can be found, for example in Oppenheim and Schafer [1975]. The principal scheme of a FIR filter is shown in Figure 1-26, with all kcoefficients set equal to 1. The amplitude frequency response of the filter can be calculated using the theory of z-transform [Oppenheim and Schafer, 1975]. If the number of taps (heights over which the averaging is performed) is 512 then the filter bandwidth is around 60 Hz (29 Hz) at zero amplitude level, as shown in Figure 1-27. Both analog and digital filters were designed, tested, and built into the DPS system proved to be working stable, providing good system performance. For some of the DPS systems that were temporarily used at the Millstone Hill Observation site, it was possible to implement only a 256-tap filter because of the memory limitation. This resulted into a twice wider filter bandwidth, approximately corresponding to that of the designed analog filter. SECTION 1 GENERAL SYSTEM DESCRIPTION 1-43 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 1-25: Digital filtering algorithm. Sampled signal is averaged before the spectrum is calculated. x(n) 1 + y(n) z -1  + z -1  + z-1 ........ +  Figure 1-26: System diagram of a FIR Filter. Samples delayed by a number of unit delays (denoted by z-1) are summed with corresponding tap coefficients k. 1-44 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE 1 DIGISONDE 4D SYSTEM MANUAL 0 -120 -60 0 60 120 f, Hz Figure 1-27: Calculated amplitude frequency characteristic of the digital filter. RF SYSTEM DESIGN CONSIDERATIONS 199. The detailed design and synthesis of a RF measurement system (or any electronic system) must be based on several criteria: a. The performance requirements necessary to provide the needed functions, in this case scientific measurements of electron densities and motions in the ionosphere. b. The availability of technology to implement such a capability. c. The cost of purchasing or developing such technology. d. The risk involved in depending on certain technologies, especially if some of the technology needs to be developed. e. The capabilities of the intended user of the system, and its expected willingness to learn to use and maintain it; i.e., how complicated can the operation be before the user will give up and not try to learn it. 200. The question of what technology can be brought to bear on the realization of a new ionospheric sounder was answered in a survey of existing technology in 1989, when the DPS portable sounder development started in earnest. This survey showed the following available components, which showed promise in creating a smaller, less costly, more powerful instrument. Many of these components were not available when the previous generation of Digisondes™ (circa 1980) was being developed:  Solid-state 300 W MOSFET RF power transistors  High-speed high precision (12, 14 and 16 bit) analog to digital (A–D) converters  High-speed high precision (12 and 16 bit) digital to analog (D–A) converters  Single chip Direct Digital Synthesizers (DDS)  Wideband (up to 200 MHz) solid state op amps for linear feedback amplifiers  Wideband (4 octaves, 2–32 MHz) 90o phase shifters SECTION 1 GENERAL SYSTEM DESCRIPTION 1-45 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL  Proven Digisonde™ 256 measurement techniques  Fast, single board, microcomputer systems and supporting programming languages 201. Many of these components are inexpensive and well developed because they feed a mass market industry. The MOSFET transistors are used in Nuclear Magnetic Resonance medical imaging systems to provide the RF power to excite the resonances. The high speed D–A converters are used in high resolution graphic video display systems such as those used for high performance workstations. The DDS chips are used in cellular telephone technology, in which the chip manufacturer, Qualcomm, is an industry leader. The DSP chips are widely used in speech processing, voice recognition, image processing (including medical instrumentation). And of course, fast microcomputer boards are used by many small systems integrators which end up in a huge array of end user applications ranging from cash registers to scientific computing to industrial process controllers. 202. The performance parameters were well known at the beginning of the DPS development, since several models of ionospheric pulse sounders had preceded it. The frequency range of 1 to 20 MHz for vertical sounding was an accepted standard, and 2 to 30 MHz was accepted as a reasonable range for oblique incidence measurements. It was well known that radio waves of greater than 30 MHz often do propagate via skywave paths, however, most systems relying on skywave propagation don’t support these frequencies, so interest in this frequency band would only be limited to scientific investigations. A required power level in the 5 to 10 kW range for pulse transmitters had provided good results in the past. The measurement objectives were to simultaneously measure all seven observable parameters outlined at Paragraph 126 above in order to characterize the following physical features:  The height profile of electron density vs. altitude  Position and spatial extent of irregularity structures, gradients and waves  Motion vectors of structures and waves 1-46 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL BIBLIOGRAPHY Barker R.H., “Group Synchronizing of Binary Digital Systems”, Communication Theory, London, pp. 273-287, 1953 Bibl, K. and Reinisch B.W., “Digisonde 128P, An Advanced Ionospheric Digital Sounder”, Univ of Lowell Research Foundation, 1975. Bibl, K and Reinisch B.W., “The Universal Digital Ionosonde”, Radio Science, Vol. 13, No. 3, pp 519-530, 1978. Bibl K., Reinisch B.W., Kitrosser D.F., “General Description of the Compact Digital Ionospheric Sounder, Digisonde 256”, Univ of Lowell Center for Atmos Rsch, 1981. Bibl K., Personal Communication, 1988. Buchau, J. and Reinisch B.W., “Electron Density Structures in the Polar F Region”, Advanced Space Research, 11, No. 10, pp 29-37, 1991. Buchau, J., Weber E.J. , Anderson D.N., Carlson H.C. Jr, Moore J.G., Reinisch B.W. and Livingston R.C., “Ionospheric Structures in the Polar Cap: Their Origin and Relation to 250 MHz Scintillation”, Radio Science, 20, No. 3, pp 325-338, May-June 1985. Bullett T., Doctoral Thesis, Univ of Massachusetts, Lowell, 1993. Chen, F., “Plasma Physics and Nuclear Engineering”, Prentice-Hall, 1987. Coll D.C., “Convoluted Codes”, Proc of IRE, Vol. 49, No 7, 1961. Davies, K., “Ionospheric Radio”, IEE Electromagnetic Wave Series 31, 1989. Golay M.S., “Complementary Codes”, IRE Trans. on Information Theory, April 1961. Huffman D. A., “The Generation of Impulse-Equivalent Pulse Trains”, IRE Trans. on Information Theory, IT-8, Sep 1962. Haines, D.M., “A Portable Ionosonde Using Coherent Spread Spectrum Waveforms for Remote Sensing of the Ionosphere”, UMLCAR, 1994. Hayt, W. H., “Engineering Electromagnetics”, McGraw-Hill, 1974. Murali, M.R., “Digital Beamforming for an Ionospheric HF Sounder”, Univ of Massachusetts, Lowell, Masters Thesis, August 1993. Oppenheim, A. V., and R. W. Schafer, "Digital Signal Processing", Prentice Hall, 1976. Peebles, P. Z., “Communication System Principles”, Addison-Wesley, 1979. Reinisch, B.W., “New Techniques in Ground-Based Ionospheric Sounding and Studies”, Radio Science, 21, No. 3, May-June 1987. Reinisch, B.W., Buchau, J. and Weber, E.J., “Digital Ionosonde Observations of the Polar Cap F Region Convection”, Physica Scripta, 36, pp. 372-377, 1987. Reinisch, B. W., et al., “The Digisonde 256 Ionospheric Sounder World Ionosphere/ Thermosphere Study, WITS Handbook, Vol. 2, Ed. by C. H. Liu, December 1989. Reinisch, B.W., Haines, D.M. and Kuklinski, W.S., “The New Portable Digisonde for Vertical and Oblique Sounding,” AGARD-CP-502, February 1992. SECTION 1 GENERAL SYSTEM DESCRIPTION 1-47 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Rush, C.M., “An Ionospheric Observation Network for use in Short-term Propagation Predictions”, Telecomm, J., 43, p 544, 1978. Sarwate D.V. and Pursley M.B., “Crosscorrelation Properties of Pseudorandom and Related Sequences”, Proc. of the IEEE, Vol 68, No 5, May 1980. Scali, J.L., “Online Digisonde Drift Analysis”, User’s Manual, University of Massachusetts Lowell Center for Atmospheric Research, 1993. Schmidt G., Ruster R. and Czechowsky, P., “Complementary Code and Digital Filtering for Detection of Weak VHF Radar Signals from the Mesosphere”, IEEE Trans on Geoscience Electronics, May 1979. Wright, J.W. and Pitteway M.L.V., “Data Processing for the Dynasonde”, J. Geophys. Rsch, 87, p 1589, 1986. 1-48 SECTION 1 GENERAL SYSTEM DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL SECTION 2 INSTALLATION, SETTING UP AND FIELD VALIDATION _______________________________________________________________________________ SECTION CONTENTS Page SECTION 2 2-1 GENERAL SOUNDER CONFIGURATION .................................................................................... 2-4 PRE-INSTALLATION CHECK ....................................................................................................... 2-5 EXTERNAL CONNECTIONS ......................................................................................................... 2-5 ANTENNA INSTALLATION ....................................................................................................................... 2-5 General Requirements .......................................................................................................................... 2-5 Vegitation/Conductive Obstructions.................................................................................................. 2-5 Antennas not on level terrain ............................................................................................................ 2-5 Lightning Protection .......................................................................................................................... 2-6 Distance Contraints........................................................................................................................... 2-6 Transmit Antenna .................................................................................................................................. 2-6 Transmit Antenna Interface Requirements ....................................................................................... 2-7 Receive Antenna ................................................................................................................................... 2-7 Receive Antenna General Description.............................................................................................. 2-7 Receive Antenna Array Layout ......................................................................................................... 2-8 Antenna Cable Connections ............................................................................................................. 2-9 INSTALLING THE GLOBAL POSITIONING SYSTEM (GPS) RECEIVER ............................................. 2-10 CONNECTING COMPUTER PERIPHERALS......................................................................................... 2-10 CONNECTING TO THE WIDE AREA NETWORK (WAN)...................................................................... 2-10 ELECTRICAL POWER CONNECTION................................................................................................... 2-10 Optional External Battery .................................................................................................................... 2-10 Battery Supply Interface ...................................................................................................................... 2-11 POWERING UP PROCEDURE .................................................................................................... 2-12 POWERING ON THE MAIN SYSTEM .................................................................................................... 2-12 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-1 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL POWERING ON THE RF AMPLIFIER AND ANTENNA SUB-SYSTEM ................................................. 2-12 CONFIGURATION MANAGEMENT OF SITE-SPECIFIC DATA ................................................. 2-13 RECEIVER ANTENNA ARRAY CONFIGURATION................................................................................ 2-14 RESTRICTED FREQUENCIES ............................................................................................................... 2-16 SUMMARY OF STATION PERSONALIZATION SETTINGS .................................................................. 2-16 FIELD VALIDATION ..................................................................................................................... 2-17 PRELIMINARY REQUIREMENTS........................................................................................................... 2-17 CROSS-CHANNEL EQUALIZING VIA INTERNAL LOOPBACK (EXCLUDING ANTENNAS AND CABLES) .................................................................................................................................................. 2-17 VERIFICATION OF CABLES AND ANTENNA PRE-AMPLIFIERS VIA EXTERNAL LOOPBACK......... 2-18 Matching antenna cable lengths.......................................................................................................... 2-19 Verification of Rx combined phase response ...................................................................................... 2-19 FIELD VALIDATION OF INSTALLED ANTENNAS AND CABLES ......................................................... 2-21 VERIFICATION OF DIRECTIONAL MEASUREMENTS IN SEMI-EXTERNAL LOOPBACK ................. 2-24 POST INSTALLATION CHECKS............................................................................................................. 2-24 2-2 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL List of Figures Figure 2-1: Standard Receive Antenna Array Orientation and Spatial Dimensions 2-9 Figure 2-2: Receive Antenna Spatial Dimensions 2-8 Figure 2-3: Location of the Front Panel ON/OFF switch for the Power Amplifier 2-11 Figure 2-4: Location of the Rear Panel ON/OFF switch and connectors 2-11 Figure 2-5: DCART Welcome Screen 2-12 Figure 2-6: Two common Digisonde 4D Antenna Layouts 2-15 Figure 2-7: Program for Cross-Channel Equalization. 2-18 Figure 2-8: Calibration of Combined Phase Response of Cables, Preamplifiers and Antenna Switch. 2-19 Figure 2-9: Program for external loopback validation of Digisonde 4D receiver setup. 2-20 Figure 2-10: Data from external loopback validation of Digisonde 4D receiver setup. 2-21 Figure 2-11: Ionogram (a) and skymap (b) for almost overhead ionosphere - no test cables inserted. 2-22 Figure 2-12: Rx Antenna Calibration setup with added test cable segments: standard antenna layout 2-22 Figure 2-13: Rx Antenna Calibration setup with added test cable segments: mirror antenna layout 2-23 Figure 2-14: Configuring DCART to label ionogram echoes during the tipped antenna array test. 2-23 Figure 2-15: Ionogram (a) and skymap (b) obtained with extension cables inserted. Skymap shows apparent shift of 10° zenith to East (azimuth 89°), and ionogram echoes are tagged as oblique East. 2-24 List of Tables Table 2-1: Software Configuration Files holding site-specific data Table 2-2: Antenna Positons for Standard and Mirror Antenna Layouts, assuming MAXDIST of 60 m 2-13 2-15 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-3 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL GENERAL WARNINGS 1. ALTHOUGH THE SOUNDER HAS BEEN DESIGNED FOR RELATIVELY SIMPLE INSTALLATION, THE COMPLETE PROCESS, INCLUDING FIELD CALIBRATION AND GAINING ACCESS TO THE INSIDE OF THE SOUNDER, REQUIRES SPECIAL KNOWLEDGE GAINED BY ATTENDANCE AT A TRAINING COURSE AND INCULCATION OF THE REQUIRED PRACTICAL SKILLS. THEREFORE NO ATTEMPT SHOULD MADE TO INSTALL, CONNECT POWER TO, OR CALIBRATE THE SOUNDER AND ITS ANCILLARY DEVICES BY UNQUALIFIED PERSONS. 2. WHEN PACKED FOR SHIPMENT THE SOUNDER WEIGHS APPROXIMATELY 60 KGS. THEREFORE AT ALL TIMES AT LEAST TWO PERSONS MUST LIFT AND CARRY THE EQUIPMENT SAFELY BY THE CASE CARRYING HANDLES. 3. NO AUTHORISED INSTALLATION, OPERATION OR MAINTENANCE TASK REQUIRES THE MAIN AND POWER AMPLIFIER CHASSIS TO BE EXTENDED OUT OF THE CASE AT THE SAME TIME. IF BOTH ARE EXTENDED, THE COMBINED MASS OF THE TWO CHASSIS, WILL ALTER THE SOUNDER’S CENTER OF GRAVITY AND WILL CAUSE THE EQUIPMENT TO TOPPLE FORWARD POTENTIALLY CAUSING INJURY TO PEOPLE AND/OR DAMAGE TO CABLES AND OTHER EQUIPMENT. CHAPTER 1 GENERAL SOUNDER CONFIGURATION 201. The sounder is provided with a fiberglass field transit case (see Figure 1-1) which is also used to protect the internal components during normal use. During installation, all external connections to the sounder are made with both chassis secured in their normal operating position (i.e., closed) and the rear shipping cover in place. The front cover should normally be left in place during normal operation. 202. Under normal operating conditions, the sounder and most of its ancillary equipment, including a monitor and keyboard, shall be installed in a clean, air-conditioned environment. It will normally be placed on a level table, with no special or fixed mounting requirements being necessary. Desirably, the table shall also serve as a operator’s and maintainer’s work bench. Its exact position shall be dictated by the proximity to any antenna through-wall feeders specified by the facility design. 203. A single phase double power outlet will be required within approximately 2 m of the table. Where back-up power is required, provision shall be made to fit two sealed lead-acid batteries directly under the table, with allowance to connect the batteries to the sounder by two 2 m cables. 204. Specifications on the sounder hardware are provided in Section 6 and Annex A of the manual. 2-4 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL PRE-INSTALLATION CHECK 205. Prior to installation, place the sounder on a table preferably in the position where it will be permanently operated. Allow at least 40 cm clearance between the rear of the case and any vertical surface to provide access to the rear I/O panel. 206. Remove the front and rear covers and inspect all external fittings for damage. Replace the rear cover before making any cable connections. In turn, release each chassis from the case, remove the chassis cover and inspect for shipping damage. Check for and make good any loose connectors and unseated cards. EXTERNAL CONNECTIONS ANTENNA INSTALLATION General Requirements Vegitation/Conductive Obstructions 207. The antenna field consists of one or two transmit antennas (customer furnished equipment), and four receive antenna stations. The installation site requires to be cleared and kept cleared of all vegetation within a 0.5 m radius from the antenna and isolated from conductive obstructions by at least a ratio of 10:1 (separation distance : longest dimensions of the obstruction). 208. The transmit antenna mast must not be closer than 30 m to the closest receive antenna station, and desirably should not be more than 130 m from the sounder. If required by site constraints, however, the transmit antenna may be installed up to a maximum of 1500 m from the sounder. If this is the case, advice on correct feeder cable selection should be sought from the antenna or cable manufacturer. 209. Any of the receive antennas should be at least 16 meters, preferably a little more, from any part of the transmit antenna. 210. The receive antennas should be at least 7 meters, preferably a little more, from any fence, wall, or building which has horizontal, metallic structure. 211. Trees are probably not a serious issue, but they certainly should not overhang the antennas. Ideally, looking upward from any antenna there should be a 45 degree (measured from zenith) cone clear of any obstruction. Other antennas or masts, such as GPS antennas, which do not have significant horizontal extent are probably not an issue as long as they are not inside the above described cone. 212. The receive antennas must be as far as possible from high voltage power transmission lines. It is difficult to be specific since the noise radiated from such lines varies tremendously. Certainly an antenna should be at least 10 meters away from even the lowest voltage overhead power lines. 213. There is the potential for mercury vapor or high pressure sodium lights to generate considerable electrical noise affecting the receive antennas. UMLCAR recommends seperating receive antennas from mercury vapor or high pressure sodium lights by 10 meters. Antennas not on level terrain SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-5 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 214. Ideally, the area the transmit and receive antennas are installed will be flat and level. This is more critical for the transmit antenna where one will encounter physical or mechanical problems if the center of the antenna and the four corners differ more than a meter or so in height. The transmit antennas’ concrete foundation must be laid on level ground. 215. However the receiving antenna field may have a uniform gradient of up to 10. If the site is not level, do not attempt to “flatten” the array by raising individual antennas (i.e., by extending the legs.) The receive loop antennas should be installed at roughly (within 1/2 meter) the same height above the ground since the performance of the antennas is somewhat dependent on the antennas height above the ground. After installation UMLCAR will add "correction cables" to the higher antennas to electrically put the antennas in the same horizontal plane. To do this we must know the measured relative heights of the antennas to 0.2 meters or so. We will then fabricate cables to be added the the higher antennas of length 2/3 (assuming a cable velocity factor or 0.66) the height difference between the higher antenna and the lowest antenna. Alternatively, the short RG-58 cables between the lightening suppressors and the back of the DPS-4D box can be shortened by 2/3 the height difference between the highest antenna and the lower antennas. Lightning Protection 216. Surge protectors are fitted on all external cables (two Tx antennas, four Rx antennas, and GPS receiver) in order to reduce the effects of lightning surge upon the sounder and ancillary items. CAUTION BECAUSE OF THE LONG CABLES, INSTALLATION OF THE RECEIVE ANTENNAS AT A DISTANCE MORE THAN 130 METRES FROM THE SOUNDER INCREASES THE EFFECTS OF LIGHTNING. Distance Contraints 217. The following spatial distance constraints in the system layout must be adhered to in order to ensure optimum operation: a. The distance from the center receive antenna station (Antenna # 1) to the sounder should not be more than 100 m. b. The distances between the three antennas at the corners of the equilateral triangle should be the same to within 1 meter. Similarly, the distances from the center antenna to the three corners of the triangle should be the same within 1 meter. c. If there are difficulties with the receive antenna layout, it is allowable to reduce the size of the triangle from 60 meters to 45 meters. If space permits, the default receive antenna array orientation is to have one leg of the triangle running North - South Geographically, (not Magnetic as shown on the attached drawing) but this is not critical and secondary to some other considerations. In any case, it will be necessary to know the relative positions of the four receive antennas with 1/2 meter accuracy for the DPS-4D configuration files. d. If there is any question about the proper positioning of the Receive Loop antennas, particularly in regard to proximity to obstructions and the transmit antenna, it might be best to install them temporarily, just sitting on top of the ground, and pour concrete only after UMLCAR has evaluated the performance of the antennas. Transmit Antenna 2-6 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 218. The crossed delta transmit antenna has been designed by UMLCAR using the NEC modelling program. The design objectives were for a simple antenna to optimally transmit vertically circular polarization over 2 to 15 MHz. It is built for UMLCAR by TCI, a major antenna manufacturer. The tower is 30.5 meters (100 ft.) high. It will require a square ground area 44 meters x 44 meters (144 ft. x 144 ft.) for installation. In addition there are recomendations for spacing from the receive antennas. 219. With this TCI implementation of the design, the four elements attached to the top of the tower are also used as guy wires. The four elements / guy wires must be attached to ground anchors embedded in concrete according to the TCI instructions. The other two sets of guy wires lower on the tower have "egg" type insulators to break up the wires electrically. The TCI installation manual has specifications for the concrete base for the tower itself, for concrete ground anchors for the 4 top elements / guy wires, and for the 3 concrete ground anchors for the lower sets of guy wires. 220. The Baluns are attached to the tower at the top. The Termination Resistors are attached at the bottom. The two coaxial cables which feed the baluns at the top of the tower are attached to the tower every meter or two. Transmit Antenna Interface Requirements Mechanical 221. The two transmit antenna feeder cables of equal length are connected to the sounder rear I/O panel by N-to-BNC through-wall connectors. According to site facility requirements, in some instances the antenna feeder cables might be terminated at a wall adjacent to the sounder. In this case, equal length, short intermediate cables may be used to connect the sounder to the through-wall connector. Electrical 222. The sounder supplies RF energy to the transmit antenna. No HV electrical power is required nor supplied by the system. Receive Antenna Receive Antenna General Description 223. The receive antenna is an array of four crossed loop antennas. Each of the antennas is comprised of two loop antennas at right angles to each other. The Pre-amp / Polarization Switch mounted under the crossed loop antenna then combines the signals from each of the two loops to receive lefthand or righthand circularly polarized waves from overhead. Each crossed loop antenna ocupies a square 1.2 meters x 1.2 meters (4 ft. x 4 ft.) and stands about 1.5 meters (6 ft.) high (see Figure 2-1). SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-7 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 2-1: Receive Antenna Spatial Dimensions Receive Antenna Array Layout 224. The sounder installation uses a receive antenna array consisting of four antenna stations, three of which form an equilateral triangle, the fourth station is located at its centriod. Figure 2-2 details array layout measurements and antenna orientation. The location of each crossed-loop antenna station in each antenna field shall be in accordance with the installation drawings. 225. Deviations from the standard antenna array configuration shown in Figure 2-2 are acceptable if the available space for the antenna field does not accommodate the standard configuration. Deviations shall be properly reflected in the station personalization files (see Paragraph 249, et seq.). 226. The orientation of the individual antennas is not critical as long as all four receive antennas are parallel to each other within 1 degree. I.e., if one antenna has its legs NW, NE, SE, and SW, then the other antennas must have their legs positioned exactly the same. Most commonly one loop is positioned magnetic North - South, and the other loop is positioned magnetic East - West. 227. Orienting the antenna array with respect to the Geographic North simplifies configuration of the analysis software. If orientation is done with respect to the ground level compass North, the configuration files need to store deviation of the antenna array axis from the Geographic North at the time of installation to account for movement of the magnetic Morth Pole with time. 228. The vertical plane polarization and East-West (i.e., orientation of North-south loop planes) of all four turnstile antennas must be within 1 of the datum line. All antenna preamplifier boxes must be oriented identically on each receive antenna station. Orientation of the Antenna #3 / Antenna #2 side of the triangle should be preferably geographic North, or magnetic compass North (see Figure 2-2). 229. Each receive antenna station comprises four crossed-loop active elements. Physical details of the antenna station including its concrete footing are provided in Figure 2-1 showing a small concrete pad for 2-8 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL each antenna leg. There certainly are alternative ways of installing the antennas depending on local weather and soil conditions. However the antenna legs are installed, the antennas should be restrained from being blown around by wind or being inadvertently moved from position. The Polarization Switch (pre-amp) mounted under the lower cross of the loops should be high enough to be out of any vegetation or snow. Figure 2-2: Standard Receive Antenna Array Orientation and Spatial Dimensions Antenna Cable Connections 230. Connect each transmit and receive antenna directly to the sounder (or to the facility’s wall termination panel) by a length of RG-213/U cable, terminated with a male “N” type connector. The four receive antennas cable lengths must be matched to within 75 mm of each other, similarly with any intermediate cables if used. The recommended cable length to minimise the risk of lightning strike is 130 m, for optimum electrical performance however a maximum length of 153 m may be used. For greater distances consultation with the cable manufacturer is suggested. 231. Connect the two transmit antenna cables to the TX1 and TX2 outputs on the sounder’s rear I/O panel. CAUTION EACH ANTENNA MUST ONLY BE CONNECTED TO ITS RESPECTIVE REAR I/O PANEL CONNECTOR ( E.G., ANTENNA #1 TO CONNECTOR #1) 232. Connect the four receive antenna cables to the respective RX1, RX2, RX3 and RX4 connectors on the rear I/O panel. When installing the receive antenna array and running the cables, verification must be SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-9 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL made to confirm that the markings at the sounder end of the cable corresponds to the respective receive antenna location as shown in Figure 2-2. INSTALLING THE GLOBAL POSITIONING SYSTEM (GPS) RECEIVER 233. The sounder derives absolute time from the external GPS receiver that is part of the sounder subsystem. The GPS receiver is connected over the serial port to the Data Platform, where it is used by Windows operating system to maintain synchronism of the Data Platform clock to the UT. The GPS also provides 1 PPS “heartbeat” signal to accurately synchronize Digisonde 4D hardware timing to the GPS. The Control Platform clock is synchronized with UT by periodic messages from Data Platform carrying UT stamp that will be effective at the next 1 PPS event. 234. The current model of GPS receiver is the Trimble Navigation Acutime receiver which is a single self-contained unit, weighing less then 500 g. A 15 m interface cable fitted with a lightning surge suppresser is supplied with the receiver. The receiver is also shipped with a threaded section of pipe and mounting flange. 235. Mount the receiver in an area open to the sky, typically on top of the shelter building, making sure that it is fixed in a vertical position using 6 mm x 25 mm cadmium plated bolts, and with a relatively unobstructed line of sight to the horizon. Connect the receiver to the sounder using the interface cable, with the 7-pin Conxall connector connected to the receiver and the 9-pin sub-D connector connected to the GPS port on the back of the rear I/O panel (see Figure 1-7). CONNECTING COMPUTER PERIPHERALS 236. The Data computer monitor is connected independently to the electrical power supplied to the site. Refer to the equipment manufacturer’s instructions to ensure that proper safety procedures are carried out. 237. The user should connect the monitor to a video output connector (VGA) and a keyboard to the 5-pin DIN plug as shown in the diagram. CONNECTING TO THE WIDE AREA NETWORK (WAN) 238. The sounder uses standard Ethernet RJ45 cable for connections to the WAN. ELECTRICAL POWER CONNECTION 239. Standard 3-pin EIA connector is fitted on the rear panel for connection of the sounder to the main power supply. An appropriate power strip is needed for connection to the main power outlet supporting range of voltages 110-240 VAC and 50/60 Hz. Optional External Battery 240. Two external 12 V battery in series can be connected to the Digisonde 4D to sustain its operations through periods of temporarily loss of main power. To connect external power to the sounder: a. Make sure that the ON/OFF switches on the power amplifier chassis and the rear I/O panel are both in the OFF (down) position (see Figure 2-3 and Figure 2-4). b. Ensure that the site mains power at the general purpose power outlet to be used for the sounder is OFF. c. Connect the battery harness to the 5-pin “BATT IN” socket (see Figure 2-4) and the system battery input cable to the battery input jack. 2-10 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL d. Turn on the power at the general purpose power outlet; the batteries will begin to charge immediately even though the sounder’s main power switch is in the off position. Refer to Sections 4 and 6 of this manual for an overview of battery charging and power distribution. ON/OFF switch of the Power Amplifier Chassis Figure 2-3: Location of the Front Panel ON/OFF switch for the Power Amplifier Main ON/OFF switch of the Rear Panel Figure 2-4: Location of the Rear Panel ON/OFF switch and connectors Battery Supply Interface 241. The sounder has an integrated battery interface which prevents the system from drawing current from the batteries unless the two batteries total more than 24 V. If the battery voltage is too low, this circuit will keep the batteries disconnected until the charging current brings them up to the correct voltage. The il- SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-11 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL lumination of the green LED next to the LCD voltmeter display on the battery interface box indicates that the batteries are connected. POWERING UP PROCEDURE POWERING ON THE MAIN SYSTEM 242. At this stage the sounder should be correctly connected to the: a. correct power source, and all power switches in the OFF (down) position, b. transmit and receive antennas, c. GPS receiver, and d. external computer monitor and keyboard. 243. Switch the ON/OFF switch on the rear I/O panel to ON. This will activate the cooling fans, switch the power relay in the lower chassis, and boot the Control and Data computers. 244. At the completion of the boot-up sequence, which will take over one minute, the DCART control software will display the welcome screen (Figure 2-5). Figure 2-5: DCART Welcome Screen POWERING ON THE RF AMPLIFIER AND ANTENNA SUB-SYSTEM 2-12 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL CAUTION THE TRANSMIT ANTENNAS MUST BE CONNECTED TO THE SOUNDER PRIOR TO APPLYING POWER 245. To power on the RF amplifier, simply turn the power switch on the front panel of the Power Amplifier Switch to ON. NOTE The power switch on the Power Amplifier Chassis front panel energizes the power amplifier ONLY, not the entire system. CONFIGURATION MANAGEMENT OF SITE-SPECIFIC DATA 246. Each sounder is pre-configured for its destination site prior to shipment. However, site-specific data may need to be adjusted in case of relocation, changes to instrument configuration, or availability of more precise site-specific data. 247. The following ID tags are assigned to each sounder: STATION ID. A unique 3-digit number that is used to label all data products. REQUIRED. Post-analysis software reads the Station ID from the data records to locate Station UDD file with station constants, including location at which they were acquired and the sounder configuration. The Station ID shall be changed if the sounder is relocated, unless its operations imply constant relocation. Changes to Station ID shall be coordinated with UMLCAR where a repository of Station IDs is maintained to avoid conflicts with existing IDs. It is possible to keep history of minor configuration changes in Station UDD file without changing the Station ID. For example, it is possible to reflect upgrades to the sounder’s hardware and antenna array pattern and retain the same Station ID. URSI CODE. A unique 5-character code given by the URSI to observatories. REQUIRED. The URSI code is associated with the location of the sounder, not its model or hardware configuration. The URSI Code is written in the SAO records holding ionogram-derived data to be reported to the WDC and other users. SERIAL NUMBER. A unique number given to each DPS sounder made by UMLCAR, in the sequence of their production. PROVIDED BY UMLCAR. Serial number is only displayed on the sounder’s homepage and not stored with the data. 248. Site-specific information can be found in the text files holding software configuration data. Table 2-1 enlists the configuration files. FILENAME DCART.INI xxx.UDD Table 2-1: Software Configuration Files holding site-specific data LOCATION GENERAL DESCRIPTION D:\DISPATCH\ Defines the Station ID for the sounder, stores configuration data for DCART processing D:\DISPATCH\UDD\ Station UDD file. Provides station constants for post-processing and visualization software. Stores records of changes to ensure that retrospective data are processed SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-13 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL (xxx = Station ID) DDASETUP.ONL DISPATCH.UDD D:\DISPATCH\ D:\DISPATCH\ correctly. Station ID files are kept at UMLCAR under version control management and distributed together with the analysis software to other users of digisonde data Provides station constants for the DDAV software Stores time zone specifics and text of labels for the web scripts supporting homepage operations of the sounder RECEIVER ANTENNA ARRAY CONFIGURATION 249. Knowledge of antenna array configuration is required for interpretation of oblique beam codes stored in directional ionograms and for all software that processes four-channel data. 250. Four-channel data are processed using full specification of the antenna array given in the Station UDD file. Full specification of any antenna array (standard or non-standard) includes: ANTENNA POSITIONS (X,Y,Z) specified in the right-hand system of coordinates with the central antenna #1 placed at the origin (0,0,0) and Z axis pointing up. DECLINATION ANGLE of the X axis of the coordinate system from Geographic North Pole, using positive angles for clockwise direction from X axis towards the North Pole. NOTE It is customary to select X axis parallel to a side of antenna array and pointing towards North (see Figure 2-2, where X axis is line connecting antenna #2 and #3). In this case Y Axis of the coordinate system points due West. 251. Aligning antenna pattern with respect to the Geographic North as in the Figure 2-2 is preferable, in which case the X-axis Declination Angle is zero. Use of the ground level compass North to orient antenna array is often more convenient. Such orientation is acceptable, as long as the X-axis Declination Angle at the time of installation (equal to the Declination angle of the magnetic field) is recorded in the Station UDD file. 252. When antenna field allows placement of antennas in one of the standard configurations, the following parameters are specified for the software that processes four-channel data: ANTENNA LAYOUT, which can be standard or mirror (Figure 2-6). In the standard Antenna Layout, enumeration of antennas 2-3-4 goes counter-clockwise. In the mirror Antenna Layout, antennas 2-3-4 are enumerated clockwise. In either cases, the antenna triangle is equilateral with the length of the side specified as ANTENNA MAXDIST. Table 2-2 specifies Antenna Positions for standard and mirror configurations in the assumption of the X axis going from antenna 3 to antenna 2. ANTENNA MAXDIST is the maximum distance between any two antennas in the configuration. ANTENNA DEVN is the deviation angle of the line connecting antenna 3 and 1 from the X axis of the antenna coordinate system, positive for counter-clockwise deviation. 2-14 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 2-6: Two common Digisonde 4D Antenna Layouts Table 2-2: Antenna Positons for Standard and Mirror Antenna Layouts, assuming MAXDIST of 60 m LAYOUT Coord Ant 1 Ant 2 Ant 3 Ant 4 STANDARD X 0 30 m -30 m 0 Y 0 17.32 m 17.32 m -34.64 m Z 0 0 0 0 MIRROR X 0 30 m -30 m 0 Y 0 -17.32 m -17.32 m 34.64 m Z 0 0 0 0 253. For the standard Digisonde 4D antenna configuration depicted in Figure 2-2: ANTENNA LAYOUT is STANDARD, ANTENNA MAXDIST is 60 m, ANTENNA DEVN is -30 degrees, and DECLINATION ANGLE is 0 degrees. 254. For antenna configurations that deviate from the equilateral triangle as in the Figure 2-6, ANTENNA LAYOUT is NON_STANDARD and only ANTENNA POSITIONS and DECLINATION ANGLE are applicable. 255. Directional ionogram data are processed using reduced specification of the antenna array given in the Station UDD file. Ionogram visualization software uses reduced specification to interpret beam codes stored in the ionogram file. Reduced specification of any antenna array is: SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-15 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL ANTENNA PATTERN, which can be one of the following four options: 0 = Standard per manual 1 = Rotated 180 degrees 2 = Mirror 3 = None of the above RESTRICTED FREQUENCIES 256. Refer to the frequency authorization operating license obtained for the sounder at the installation site and note any frequencies to be protected. The restricted frequency intervals are stored in ImposedRestriction.UDD file in the D:\DISPATCH\ folder of the Data Platform. Restrictions are specified as the lower end and upper end of each frequency band to be avoided during transmission. The bands are commaseparated; multiple *946 lines can be provided in one file, e.g.: *946 < 40000-45000, 70000-75000 > *946 < 81500-82150 > SUMMARY OF STATION PERSONALIZATION SETTINGS 257. Table 3-2 summarizes all station-specific configuration items that need to be personalized for the sounder. Table 3-2: Site-specific configuration items to personalize for DPS-4D FILENAME ITEM # CONTENTS SOFTWARE COMPONENT DCART.INI1 SID Station ID DCART: tagging of data files See Section 5 for description of other DCART options ImposedRestrictions.udd 946 Restricted frequencies DCART Station UDD file (xxx.UDD) 304 Station name 101 Geographic latitude DCART, ARTIST 5, DFT2SKY, TILT, DRGMaker, online image tools, SAO Explorer 102 Geographic longitude 104 Gyrofrequency 105 Dip angle 106 Magnetic declination 307 URSI Code 032 Digisonde model 079 X AXIS DECLINATION ANGLE 080-082 ANTENNA POSITIONS 086 ANTENNA PATTERN 090 ANTENNA LAYOUT 091 ANTENNA DEVN 1 DCART.INI file should not be edited directly, but rather via the DCART Options menu selections. 2-16 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL FILENAME DISPATCH.UDD DDASETUP.ONL ITEM # 092 055 130 133-137 185 184, 170, 177 CONTENTS ANTENNA MAXDIST URSI Code Display title Local time and daylight savings Station constants Antenna coordinates SOFTWARE COMPONENT Dispatcher: filename generation Web scripts: display Web scripts: display DDAV : drift velocity calculations FIELD VALIDATION CAUTION AT ANY TIME DO NOT PATCH TX1 OR TX2 DIRECTLY INTO ANY OF THE RX CONNECTORS ON THE REAR I/O PANEL TO SET UP A LOOPBACK. THE RX CONNECTORS HAVE 24 VDC ON THEM TO POWER THE RECEIVE ANTENNAS. TO CONNECT AN EXTERNAL LOOPBACK, BLOCKING CAPACITORS MUST BE CONNECTED IN SERIES WITH THE ANTENNA SWITCH INPUTS AT THE REAR OF THE MAIN CHASSIS. 258. Although the sounder is subjected to detailed testing during manufacture and prior to shipping, final system validation must be completed in the sounder’s ultimate operating environment to ensure that the sounder and antenna sub-systems are correctly matched and deliver optimum performance. Field validation process involves: a. Matching the antenna cable lengths, b. Adjustments to the cable lengths for varying antenna heights, c. Detecting defective cables and Antenna Pre-amps, d. Verifying the correct directions in both Ionogram and Drift modes of operation. PRELIMINARY REQUIREMENTS 259. Field calibration shall only be performed by personal who have qualified on an authorised Digisonde Sounder training course, and who have access to the relevant calibration equipment specified in this section. Proficiency in sounder operations as described in Section 3 of this manual is mandatory. 260. Before any field calibration is performed the sounder and antenna sub-systems must be installed as per the preceding instructions. CROSS-CHANNEL EQUALIZING VIA INTERNAL LOOPBACK (EXCLUDING ANTENNAS AND CABLES) 261. Identical response of all receive channels of the Digisonde 4D to the input signal is required to ensure correct directional analysis of four-channel data. Frequency-dependent mismatches in phase and ampli- SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-17 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL tude resonse characteristics are introduced primarily by the narrowband analog circuitry that is used in the Tracking Filter cards and analog amplifiers of the Receiver card. 262. Periodically running a Cross-Channel Equalizing program removes major part of the cross-channel, frequency-dependent phase and amplitude variation in the Digisonde 4D sounder. The results of the crosschannel equalization are saved in the LATEST.CEQ file in D:\DISPATCH\ folder. This file automatically corrects phase and amplitude differences in the four receiver channelss for all subsequent Ionogram and Drift measurements. 263. A Cross-Channel Equalizing program is configured by setting Operation mode to “Channel Equalizing” and Operation Option to “Internal Loopback” (see Figure 2-7 and Section 3). An appropriate CrossChannel Equalizing program is pre-configured prior to the sounder shipment, but it is important that its frequency coverage is appropriately adjusted with time to match the range of operating frequencies. In the Cross-channel equalizing mode with internal loopbak, the sounder: a. Switches the XMT card output through an attenuator (on the XMT card) and injects it directly into the antenna switch assembly (via the coaxial cable labelled “Cal In”). b. Disables the RF power amplifier by gating off the XMTR pulse signal (accessible on the front panel) which normally activates the bias voltage of the RF power FET. c. Switches the antenna switch inputs from the four external antennas to the directly injected transmitter signal. Figure 2-7: Program for Cross-Channel Equalization. 264. Cross-Channel Equalization program shall be run prior to checking cable lengths and the phase response of the loop antenna pre-amplifiers. VERIFICATION OF CABLES AND ANTENNA PRE-AMPLIFIERS VIA EXTERNAL LOOPBACK 265. Cable and antenna pre-amplifier verification must be performed at system installation to identify and correct phase errors, and may be repeated periodically to see if corrections are necessary. 2-18 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Matching antenna cable lengths 266. Ideally all the antenna cables should be matched to 6 inches or 20 cm. They can be matched using either physical or electrical techniques. To match physically layout cables on flat, smooth surface such as a driveway. To match electrically, use a Time Domain Reflectometer (TDR). Or there is a technique using a frequency synthesizer and oscilloscope. The far ends of the cables should either all be either open or shorted. Verification of Rx combined phase response 267. Wide-band antenna pre-amplifiers, cables, and antennas switch circiutry should not introduce frequency-dependent phase shifts. It is however recommended that the combined phase response of preamplifiers, cables, and antenna switch is verified prior to laying out the cables in the antenna field. This procedure shall be performed after the internal cross-channel calibration procedure is completed using the internal loooback as described in Paragraph 261 et seq. XMTR1 FRONT PANEL 70 dB Atten Could be 153 m (500 ft.) ZSC-3-1 S PLITTER Put 50 ohm load on unused outputs Box Ground Made by Shorting S and W Connector Center Pin to the Shield W E S N PREAMP #1 W E S N PREAMP #2 NOTE: Calibration of combined phase response of cables, preamps and antenna switch with 2– or 3–way splitter, the measurement has to be repeated keeping antenna #1 attached as a reference ANTENNA SWITCH REAR PANEL VIS 3-5 RECEIVER INPUTS Figure 2-8: Calibration of Combined Phase Response of Cables, Preamplifiers and Antenna Switch. 268. Create a new external loopback program as shown in Figure 2-9 (if it is not available in DCART already). The external loopback is arranged as an ionogram measurement with the following key features: a. Starting height set at zero (in order to observe the loopback signal), b. Gain mode selected as “create new gain table” (to ensure that receivers adjust optimally to the loopback signal), SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-19 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE c. Raw data saved in a file for later inspection d. Ionogram file is not created for the data product dissemination DIGISONDE 4D SYSTEM MANUAL Figure 2-9: Program for external loopback validation of Digisonde 4D receiver setup. 269. Once the external loopback program is completed, note the name of the created .RAW file in DCART message console and open it for inspection in DCART using “View Group Data” selection of the Action menu. The .RAW file will be located in the D:\Secure\IndividualFiles\ folder. In the Viewer window, select Doppler Data for the Display Content selector to obtain view similar to the one shown in Figure 2-10. Note that four channels shall look similar to each other at all frequencies. You can use the spider line to read four phases for two central Doppler lines that should not differ by more than 5°. 270. The phase errors (difference in measured phase angles from four in-phase source signals) in antenna response (not necessarily between receivers in a 4-channel system) should be less than 5° even without calibrated correction, so if these procedures show errors in excess of 5°, inspect the magnetic loop antennas for reversed cable connections or breaks. 271. If the connections are correct and the phase difference persists, the pre-amplifier boxes should be swapped between the antennas showing a large phase difference, and the test re-run to see if the phase difference is now the negative of what it was (indicating a problem in a pre-amplifier). 272. If errors still exceed 10°, the coaxial cable connections to the antenna switch should be swapped (e.g., connect antenna #1 to the antenna #2 input) and re-run the test to see if the inverse phase error occurs (indicating a cable length error). At this point the electronics have been eliminated as the cause of the problem, so if errors still exceed 10° the antenna cable lengths should be adjusted or the “bad” cable replaced. 2-20 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 2-10: Data from external loopback validation of Digisonde 4D receiver setup. FIELD VALIDATION OF INSTALLED ANTENNAS AND CABLES 273. With a quiet ionosphere, skymaps and RSF ionograms should generally appear to be overhead. Figure 2-11 is a sample of the skymap showing ionospheric tilt close to 0 (zenith angle of 2°, azimuth angle is irrelevant). 274. After verifying that the ionograms and skymaps generally appear to be overhead, add two test cables to artificially tilt antenna array as follows. For a four antenna array, 60 meters on a side, temporarily add a 6 meter extension to an outer antenna cable and temporarily add a 2 meter extension to the center antenna cable. This will tilt the antenna beam approximately 10 degrees in the direction away from outer antenna which has the extra cable length. Figure 2-13 and Figure 2-13 show extension cable connections and expected tilt of the antenna beam for standard and mirror antenna layouts. 275. While 10° tilt is clearly seen on a sklymap, it is necessary to set smaller zenith angle parameter for ionogram processing functions in DCART (see Figure 2-14), otherwise it will be displayed as vertical in the ionogram image. Echoes whose calculated zenith angle is greater or equal the configuration threshold value will be tagged as oblique in the RSF ionogram files. Remember to return the zenith angle setting to 15°. SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-21 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL (a) (b) Figure 2-11: Ionogram (a) and skymap (b) for almost overhead ionosphere - no test cables inserted. Figure 2-12: Rx Antenna Calibration setup with added test cable segments: standard antenna layout 2-22 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 2-13: Rx Antenna Calibration setup with added test cable segments: mirror antenna layout Figure 2-14: Configuring DCART to label ionogram echoes during the tipped antenna array test. SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION 2-23 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 276. Example ionogram and skymap onbtained in the tilted antenna array configuration are shown in Figure 2-15, where tilt is accomplished in the mirror antenna configuration, thus corresponding to the apparent eastward direction of the echoes. (a) (b) Figure 2-15: Ionogram (a) and skymap (b) obtained with extension cables inserted. Skymap shows apparent shift of 10° zenith to East (azimuth 89°), and ionogram echoes are tagged as oblique East. VERIFICATION OF DIRECTIONAL MEASUREMENTS IN SEMI-EXTERNAL LOOPBACK 277. To verify the correctness of receiver and software configurations, a known phase difference can be also created by semi-external looback measurement that feeds XMTR1 signal into four connectors on the antenna switch using a power splitter, isolation capacitors, and a set of four BNC cables each 1, 1, 3 and 7 m long. A 0.1 F series capacitor is required in each BNC receiver cable since the antenna switch supplies a DC voltage to the pre-amplifiers. This amounts to replacing the pre-amplifiers in Figure 2-8 by series capacitors. 278. Using the loopback configuration with the series capacitors as described in previous paragraph, place the 3 m cable in the antenna #1 loopback channel and the other three in any order. This simulates offvertical signal reception at about 8.5°. The external loopback ionogram program with zero starting height (see Figure 2-9) shall be used for the test, and DCART shall be configured for a smaller maximum zenith angle for the vertical echoes to display tilted loopback signal as arriving obliquely. Remember to return the zenith angle setting to 15°. POST INSTALLATION CHECKS 279. At this stage it is recommended that the operator tests the system by modifying and running measurement programs as outlined in Section 3 (Operating Modes and Instructions) of this manual. 2-24 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL SECTION 3 OPERATING INSTRUCTIONS _______________________________________________________________________________ SECTION CONTENTS Page SECTION 3 3-1 CHAPTER 1 PROGRAMMING DIGISONDE MEASUREMENTS.............................................. 3-6 PROGRAMS, SCHEDULES, AND SCHEDULE START TIMES .............................................................. 3-6 SCIENCE MODES AND DATA PRODUCTS ............................................................................................ 3-7 PROGRAMMING SCIENCE MEASUREMENTS ...................................................................................... 3-9 General Considerations......................................................................................................................... 3-9 Frequency Multiplexing ......................................................................................................................... 3-9 Frequency Stepping, Range Sampling, and Pulse Integration ........................................................... 3-11 Autogain Evaluation and Control......................................................................................................... 3-12 Programming Vertical Incidence Ionogram Measurement.................................................................. 3-15 RSF Ionogram with echo directions................................................................................................ 3-15 RSF Ionogram with echo directions and precision ranging ............................................................ 3-17 SBF Ionogram without echo directions ........................................................................................... 3-18 Data Products Derived from Vertical Incidence Ionogram Measurement........................................... 3-18 Automatic ionogram scaling with ARTIST ...................................................................................... 3-18 Presentation of directional ionogram data as daily directogram..................................................... 3-19 Programming Oblique Incidence Ionogram Measurement ................................................................. 3-21 Programming Drift Measurement ........................................................................................................ 3-22 Data Products Derived from Drift Measurement ................................................................................. 3-24 Doppler skymap .............................................................................................................................. 3-24 Bulk plasma drift velocity ................................................................................................................ 3-24 Ionospheric tilt ................................................................................................................................. 3-24 Skymap display for WWW homepage ............................................................................................ 3-24 Daily velocity plot for WWW homepage.......................................................................................... 3-25 Programming Passive RF Sensing Measurements ............................................................................ 3-25 SPECIFICATION OF RESTRICTED FREQUENCIES ............................................................................ 3-27 HOUSEKEEPING MEASUREMENTS AND DATA PRODUCTS............................................................ 3-29 COMMAND AND TELEMETRY TRAFFIC .............................................................................................. 3-29 SECTION 3 OPERATING INSTRUCTIONS 3-1 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL CHAPTER 2 BASIC OPERATION OF DCART ....................................................................... 3-32 BASIC PRINCIPLES ................................................................................................................................ 3-32 Normal and Advanced Modes of DCART Interface............................................................................. 3-32 DCART Screen Layout ........................................................................................................................ 3-33 DCART Color Concept ........................................................................................................................ 3-34 Autonomous and Manual Digisonde Operations................................................................................. 3-34 PROGSCHD Management.................................................................................................................. 3-36 Active and Edited PROGSCHD ...................................................................................................... 3-36 PROGSCHD Activation ................................................................................................................... 3-37 Offline PROGSCHD editing ............................................................................................................ 3-38 REAL-TIME DATA VISUALIZATION ....................................................................................................... 3-39 DCART Processing Chain ................................................................................................................... 3-41 Real-time Display of Time-Domain Data (steps 1-4 of Processing Chain)..................................... 3-41 Real-time Display of Doppler Spectra (step 5 of Processing Chain) .............................................. 3-42 Waterfall presentation of the drift data ............................................................................................ 3-45 Real-time Display of Ionograms (step 6 of Processing Chain) ....................................................... 3-46 Real-time Display of BIT results...................................................................................................... 3-47 OFFLINE DATA VISUALIZATION ........................................................................................................... 3-48 AUTONOMOUS OPERATIONS OF DIGISONDE 4D ............................................................................. 3-48 Basic Schedule Editing with DCART ................................................................................................... 3-49 Advanced Schedule Editing with DCART............................................................................................ 3-51 Programming SSTs with Planning Rules and Campaign Requests ................................................... 3-51 Planning Rules ................................................................................................................................ 3-52 Campaign Requests........................................................................................................................ 3-55 Real-time Display of Schedule Progression in SST Editor.................................................................. 3-55 MANUAL OPERATIONS OF DIGISONDE 4D ........................................................................................ 3-56 CHAPTER 3 DIGISONDE 4D PROGRAMMING RECOMMENDATIONS ............................... 3-58 QUALITY CONTROL OF PROGSCHD DEFINITIONS ........................................................................... 3-58 VALID PROGRAMS UNSUITABLE FOR SCIENCE OBSERVATIONS.................................................. 3-58 VALID PROGRAMS WITH POTENTIAL PROBLEMS ............................................................................ 3-58 VALID PROGRAMS SUBOPTIMAL FOR SCIENCE OBSERVATIONS ................................................. 3-58 Ionogram measurement ...................................................................................................................... 3-59 Drift measurement ............................................................................................................................... 3-59 General recommendations for program design................................................................................... 3-60 VALID SCHEDULES SUBOPTIMAL FOR SCIENCE OBSERVATIONS ................................................ 3-60 3-2 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL GENERAL RECOMMENDATIONS FOR DIGISONDE OPERATIONS .................................................. 3-60 CHAPTER 4 ADVANCED INTERFACE of DCART ................................................................ 3-62 SUMMARY OF ADVANCED FEATURES IN DCART ............................................................................. 3-62 Cross-Channel Equalizing of the Receiver Channels ......................................................................... 3-62 Calibration of Tracking Filters.............................................................................................................. 3-63 Data Production Modes ........................................................................................................................... 3-64 CHAPTER 5 HOMEPAGE AND DATA DISSEMINATION ...................................................... 3-65 INTRODUCTION ..................................................................................................................................... 3-65 CHAPTER 6 REMOTE ACCESS ............................................................................................. 3-68 INTRODUCTION ..................................................................................................................................... 3-68 REMOTE ACCESS USING REMOTE DESKTOP SOFTWARE............................................................. 3-68 REMOTE ACCESS USING FTP/SFTP CONNECTION TO DIGISONDE .............................................. 3-68 Commanding DESC operations .......................................................................................................... 3-68 Updates to PROGSCHD ..................................................................................................................... 3-69 Control of Dispatcher........................................................................................................................... 3-69 Upload of campaign requests.............................................................................................................. 3-69 SECTION 3 OPERATING INSTRUCTIONS 3-3 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL List of Figures Figure 3-1: Digisonde’s Programs, Schedules, and Schedule Start Times 3-6 Figure 3-2: Overview of the Digisonde data products and displays 3-8 Figure 3-3: Frequency multiplexing as a means to increase Doppler frequency resolution. 3-10 Figure 3-4: Frequency multiplexing in ionogram and drift measurements. 3-11 Figure 3-5: Programming frequency stepping and range sampling for ionogram and drift measurements 3-11 Figure 3-6: Gain control steps in Digisonde 4D. 3-13 Figure 3-7: “Create gain table” program that refreshes the autogain table (ionogram file is not made). 3-14 Figure 3-8: RSF ionogram with echo directions, running time ~2 minutes. 3-16 Figure 3-9: RSF ionogram with echo directions and precision ranging, running time ~4 minutes. 3-17 Figure 3-10: SBF ionogram without echo directions, antenna 3 disabled, running time ~2 minutes. 3-18 Figure 3-11: Ionogram display produced by Ion2PNG software for digisonde’s WWW homepage. 3-19 Figure 3-12: Daily directogram. (Left panel) sample directogram made by Drg2PNG software, (right panel) calculation of distance to the reflection point, Di Figure 3-13: Signal propagation during oblique incidence ionogram measurement between two digisondes. 3-20 3-21 Figure 3-14: Digisonde 4D at Jeju Island, Korea, configured to receive signal from Anyang DPS-4 (444 km ground distance) via oblique propagation. 3-22 Figure 3-15: Drift measurement program and real-time display. 3-24 Figure 3-16: Skymap display for WWW homepage. 3-25 Figure 3-17: Daily drift velocity plot for WWW homepage. 3-26 Figure 3-18: Sample passive RF sensing measurement of EISCAT signal at 4040 kHz. 3-27 Figure 3-19: Fixed-frequency passive measurement of the EISCAT signal. 3-27 Figure 3-20: Digisonde 4D computer configuration with CONTROL and DATA platforms 3-30 Figure 3-21: Configuring DCART in Normal Interface Mode (General Options) 3-32 Figure 3-22: DCART screen layout (normal interface) 3-33 Figure 3-23: Digisonde in its (a) Manual and (b) Autonomous modes of operation. Push “Auto” button to switch to the Autonomous mode. Push STOP or Soft STOP to switch to the manual mode. 3-35 Figure 3-24: Management of PROGSCHD structures by DESC and DCART software. 3-36 Figure 3-25: Display of the (a) active and (b) edited PROGSCHD in DCART. 3-37 Figure 3-26: Activation of the edited PROGSCHD. 3-38 Figure 3-27: Offline editing of external PROGSCHD files on DATA platform. 3-39 Figure 3-28: Real-time “Sounding Mode” display of DCART (disabled). 3-40 Figure 3-29: Real-time “Sounding Mode” display of DCART (enabled). 3-41 Figure 3-30: Real-time “Sounding Mode” display, Time Domain plot (steps 1-4 of the Processing Chain). 3-42 Figure 3-31: Real-time “Sounding Mode” display, Doppler Spectra plot (step 5 of the Processing Chain). 3-43 Figure 3-32: Doppler Image options for the real-time Doppler Spectra plot 3-44 Figure 3-33: Example of 15 minute ionogram schedule 3-49 Figure 3-34: Example of 15 minute ionogram schedule 3-50 3-4 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE Figure 3-35: Manual and Automatic placement modes of the Schedule Editor Figure 3-36: SST Editor List of Tables DIGISONDE 4D SYSTEM MANUAL 3-51 3-52 Table 3-1. Specification of Restricted Frequency Interval List in StationSpecific.UDD configuration file Table 3-2. DCART Processing Chain Table 3-3. Display options for Time-Domain real-time window Table 3-4. Display options for Doppler Spectra real-time window Table 3-5. Display options for Doppler Image Table 3-6. Start Conditions Table 3-7. Interval Conditions Table 3-8. Examples of priority analysis 3-28 3-41 3-41 3-43 3-44 3-53 3-54 3-55 SECTION 3 OPERATING INSTRUCTIONS 3-5 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL CHAPTER 1 PROGRAMMING DIGISONDE MEASUREMENTS PROGRAMS, SCHEDULES, AND SCHEDULE START TIMES 3:1. The Digisonde is a configurable scientific instrument that offers a variety of measurement modes and corresponding data products. The basis of all its operations is a measurement program, or simply program, a set of operational parameters that define one logically complete set of measurements performed by the digisonde. For example, a digisonde program can define an ionogram measurement. Digisonde 4D keeps up to 256 active program definitions in its memory. System software includes a Program Task that is responsible for hardware commanding and data acquisition steps needed to complete program per its definition. 3:2. A measurement program can be started manually by a keyboard/mouse command or, for the autonomous operations, triggered by the system software in accordance with the current schedule, a repetitive sequence of measurement programs (Figure 3-1). For example, a digisonde schedule can instruct digisonde to make ionogram measurements every 10 minutes. When a schedule is running, its measurement programs are started automatically in the endless loop. Digisonde 4D stores up to 256 active schedule definitions in its memory. System software includes a Schedule Task that invokes the Program Task per schedule definition. Figure 3-1: Digisonde’s Programs, Schedules, and Schedule Start Times 3-6 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 3:3. A measurement schedule can be started manually by a keyboard/mouse command or, for the autonomous operations, triggered by the system software using the concept of Schedule Start Time (SST). One SST consists of (1) schedule number and (2) UT timestamp when the schedule shall be started. An SST Task is responsible for starting the Schedule Task at requested times. The SST Task periodically checks an SST Queue holding individual SSTs. When the system clock matches the earliest SST in the queue, The SST Task invokes the Schedule Task and removes expired SST from the queue. 3:4. The SST Queue has to be replenished with new SSTs that are usually calculated automatically in accordance with the top-level definition of the measurement planning. For example, such planning can have two different schedules for daytime and nighttime. Programming the digisonde to switch schedules automatically is further discussed in Chapter 2. SCIENCE MODES AND DATA PRODUCTS 3:5. The following types of scientific measurements are available for the digisonde operations: 1) Ionogram (a) Vertical Incidence (VI) ionogram:  VI ionogram with Doppler analysis of echoes  VI Doppler ionogram with evaluation of the echo’s angle of arrival Multi-beam processing Source interferometry processing  VI Doppler ionogram with multi-beam processing and two frequency precision ranging (b) Oblique Incidence (bi-static) ionogram between two digisondes 2) Drift measurement (detection of multiple echoes and evaluation of their source velocities). 3) Passive RF Sensing mode for monitoring transmitters of opportunity. 3:6. Digisonde employs data processing software to obtained derived data products from acquired ionogram and drift measurement data: 1) Ionogram-derived data (a) Automatically scaled ionospheric characteristics, ionogram traces, and electron density profile (b) Maximum Usable Frequency (MUF) report (c) Directogram showing a daily plot of oblique echoes 2) Drift-derived data (a) Skymap showing location of reflection sources (b) Drift velocity derived in the assumption of a bulk motion of plasma across the station (c) Zenith and azimuth of the ionospheric tilt 3:7. Figure 3-2 presents an overview of the Digisonde data products in terms of their origin, data storage and display options. The upper panel enlists science data types that are acquired in the process of digisonde measurements. Yellow circles are used to denote created data file types. In addition to the three major science data modes, ionogram (RSF+SBF), drift (DFT), and Passive RF Sensing (TOV), it is possible to store raw sample data (RAW). The rest of data products are derived using data post-analysis software that runs autonomously SECTION 3 OPERATING INSTRUCTIONS 3-7 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL (the lower panel). Arrows in the Figure 3-2 indicate data flow for derivation and display of the products. Two types of display are distinguished, real-time monitoring of the measurement process, and images available for viewing over the Internet (Web displays). Figure 3-2: Overview of the Digisonde data products and displays 3-8 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL PROGRAMMING SCIENCE MEASUREMENTS General Considerations 3:8. Fundamentally, ionogram and drift measurements use the same remote sensing approach described in Section 1, in which digisonde transmits a sequence of pulses on an operating frequency, listens for the echoes on its four antennas, performs signal processing (RFIM, cross-channel equalizing, pulse compression), and obtains set of four Doppler spectra for each sampled range bin (one spectrum per receiver channel). Then, in the drift measurement mode, all Doppler spectra are stored in the output product file for subsequent derivation of the skymap and bulk drift velocity, whereas in the ionogram mode, only one echo is recorded per range bin by reducing four Doppler spectra to one echo status (amplitude, Doppler shift, angle of arrival, etc.). 3:9. Practically, programming ionogram and drift measurements has several subtle differences. a. Separation of the overlapping echoes by their Doppler frequency is instrumental to the efficient skymap construction. In order to accomplish high Doppler frequency resolution necessary for the drift/skymap measurement, the coherent integration time (CIT) has to be selected as high as 20 or 40 sec, so that corresponding Doppler resolution is 0.05 or 0.025 Hz. Ionogram measurement at such high integration times per frequency would take too much time to complete, and thus integration times in the ionogram mode have to be selected much lower, in the order of 1 sec or less. b. For ionogram measurements, number of pulses per frequency, N, is kept sufficiently small to reduce the ionogram running time. Because smaller N means lower signal-to-noise ratio, such selection has to consider implications of reducing the overall ionogram quality. While such selection is station-dependent, it is generally recommended to have at least 16 pulses per frequency. Smaller N values are possible for campaign periods requiring fast ionograms (below 30 sec). In the drift mode where Doppler frequency resolution is high, number of pulses per frequency N (i.e., number of spectral lines in the Doppler spectrum) has to be as high as possible to cover sufficient range of Doppler frequencies. For example, with Doppler resolution of 0.025 Hz and 128 pulses per frequency, Doppler frequency coverage is only +/1.6 Hz, which is too small to capture ionospheric plasma movements. 256 pulses per frequency have to be used in such drift measurement. c. Drift measurement produces relatively large volume of data for storage. A number of data reduction measures are taken to keep drift file sizes reasonably small. In particular, it is customary to run drift measurement on a small subset of fixed frequencies rather than sweep the whole frequency range as in the ionogram mode. Digisonde 4D offers an automated frequency override mode, in which selected set of fixed frequencies for drift measurement is shifted up and down in frequency using data from recent autoscaled ionogram, so that these frequencies are optimally positioned to target the F region of ionosphere. Frequency Multiplexing 3:10. Frequency multiplexing is commonly used in the drift mode to effectively increase the integration time without increasing overall measurement time. To illustrate the principle of frequency multiplexing, let’s consider example where 8 pulses per frequency are transmitted, and the measurement includes 4 frequencies. Figure 3-3 shows progression of the non-multiplexed case in time. First, digisonde sends and processes 8 pulses on frequency 1, then another 8 for frequency 2, then frequency 3, and finally the last 8 pulses for frequency 4. Figure 3-3 shows frequency multiplexing when frequency sequence 1-2-3-4 is repeated 8 times. Both cases involve transmission of 8x4 = 32 pulses using the same amount of time. However, coherent integration time for SECTION 3 OPERATING INSTRUCTIONS 3-9 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL each frequency in the multiplexed case is 4 times larger, resulting in 4 times better Doppler resolution of the measurement. Further details on frequency multiplexing can be found in Section 1. Figure 3-3: Frequency multiplexing as a means to increase Doppler frequency resolution. 3:11. In order to accommodate specification of the frequency multiplexing in digisonde programs, three program parameters are used (see Figure 3-4): a. Fine frequency step (FFS) = frequency step inside a block of multiplexed frequencies b. Number of fine frequency steps (NFS) in the block c. Coarse frequency step (CFS) = frequency step between blocks of multiplexed frequencies 3-10 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-4: Frequency multiplexing in ionogram and drift measurements. 3:12. For example, suppose 50 kHz linear frequency stepping and x4 advantage in Doppler resolution is required for an ionogram. Then fine frequency step (FFS) is 50 kHz, number of fine steps (NFS) is 4, and coarse frequency step is CFS = NFS * FFS = 200 kHz. The same ionogram measurement but without x4 Doppler resolution improvement would be made by setting CFS to 50 kHz and NFS to “none” (thus disabling multiplexing). Frequency Stepping, Range Sampling, and Pulse Integration 3:13. Figure 3-5 compares two typical examples of programming frequency/range stepping and pulse integration for ionogram and drift modes. Ionogram measurement: Drift measurement: Figure 3-5: Programming frequency stepping and range sampling for ionogram and drift measurements 3:14. The left panel of Figure 3-5 specifies a frequency sweep from 0.5 to 12 MHz, typical for the ionogram mode. Frequency multiplexing is disabled, and linear frequency stepping with 50 kHz is set, resulting in 231 frequency steps in the ionogram. Interpulse period of 2 x 5 = 10 ms (1500 km radar range) is selected to accommodate 512 range steps of 2.5 km each (from 80 to 1357.5 km). Number of integrated repeats per frequency is set to 16, resulting in the Doppler spectra with 16 lines. Each integrated repeat involves 2 pulses with SECTION 3 OPERATING INSTRUCTIONS 3-11 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL complementary codes of phase modulation, and two separate transmissions for O and X polarizations. Thus 64 pulses are transmitted on each frequency, totaling 64 x 231 = 14784 pulses needed to complete the ionogram measurement. At 10 ms interpulse period, pulse transmission during this ionogram requires 14784 x 10 ms = 147.84 sec = 2m 27s 840ms. Additional 30 ms of time overhead are required to manage FIFO buffers and time synchronization, resulting in the exact ionogram running time of 2m 27s 870ms. Without multiplexing, CIT time is 64 x 10 ms = 640 ms, so that Doppler resolution is 1/0.64s = 1.5625 Hz. 3:15. Choice of the upper frequency for the ionogram sweep is determined by the maximum expected frequency at which echoes can still be observed. The upper frequency shall be high enough to accommodate unusual increases in the ionospheric plasma density. It is recommended to program daytime and nighttime ionograms separately and setup nighttime ionograms with a lower upper frequency but finer frequency steps to improve quality of the ARTIST ionogram autoscaling. 3:16. Choice of the lower frequency for the ionogram sweep is influenced by new capability of the Digisonde 4D to mitigate powerful RF interference from broadcasting stations that operate below 1.5 MHz. Depending on digisonde location and RFI environment, it may be possible to observe echoes at frequencies as low as 0.3 MHz. 3:17. Interpulse phase switching is another RFI mitigation technique in which phase of odd pulses is flipped by 180º on both transmission and reception, so that when integration of multiple pulses is performed, coherent interferers are suppressed while signals are still enhanced. 3:18. The right panel of Figure 3-5 specifies a fixed-frequency drift measurement with 4 multiplexed frequencies separated by 100 kHz. The set of 4 frequencies 100 kHz apart is positioned at 2 MHz, unless the latest data from the ionogram autoscaling is available to move the set to a more appropriate anchor frequency. With 6 repeats of 4 frequency sets, total number of frequency [operations] is 24. On each of these 24 frequencies, N = 256 integrated repetitions are made, each repetition consisting of 2 complementary codes (and only one polarization is recorded to reduce data volume). This, total number of pulses needed to complete this measurement is 24 x 512 = 12288. Although 512 pulses are sent on each frequency, frequency multiplexing provides 4x improvement in Doppler resolution, raising CIT from 512 x 10 ms = 5.12 sec (non-multiplexed) to 512 x 4 x 10 ms = 20 sec 480 ms. With this CIT duration, Doppler resolution is 0.05 Hz, and Doppler spectra cover 256 x 0.05 = +/- 6.4 Hz. 3:19. While range sampling is configured identically in both ionogram and drift mode, motivation for these choices is different. The ionogram measurement sets upper range to 1357.5 km to make sure that echoes from the raised F2 layer, whose virtual ranges can go well above 800 km during storm conditions, are still observed. Setting the interpulse period to 5 ms (thus cutting ionogram running time in half) and recording virtual ranges from 80 to 717.5 km might suffice in majority of the geophysical conditions, except perhaps the most interesting cases of the storm activity. It is therefore recommended to always use 2.5 x 512 range sampling mode during ionogram measurements. For the drift mode, choice of 10 ms for the interpulse period is driven primarily by the need to increase CIT time. Autogain Evaluation and Control 3:20. The Digisonde 4D design considers operation in noisy RF environments where strong interferers could saturate the receiver inputs rendering the receivers insensitive to smaller message signals. For ionospheric sounding, AM radio stations in the 0.55-1.65 MHz band and the 6-24 MHz HF communications bands can pose serious problems for ground-based receivers. At some locations we have measured interference levels of >1 V signals at the receive antennas compared to <1 μV message signals. Digital receivers that directly digitize RF signals are especially prone to this problem since ADCs have a limited dynamic range. The ADCs need to be protected from powerful out-of-band interference as well as from saturating in-band signals. In the Digisonde 3-12 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 4D, a combination of gain controls in the wideband input amplifiers and the analog tracking bandpass filters limit the input voltages at the ADCs to the maximum allowed values. 3:21. Figure 3-6 shows a diagram of the Receiver path in Digisonde 4D indicating gain stages. The requirement of a higher agility of the automatic gain control applies to the narrow-band circuits that are sensitive to the individual RFI sources and therefore their changes with time. Wide band circuitry is exposed to the cumulative environment where dynamics of the individual sources of interference is smeared out. Correspondingly, Digisonde 4D implements three kinds of gain control, a. Fixed Gain in antenna preamplifiers (site-specific, adjusted at the installation time) b. Constant Gain in antenna switch and tracking filters (does not change during the measurement, but can be programmed to adapt to the larger time scale changes such as day/night) c. Auto Gain (that changes from frequency to frequency) Figure 3-6: Gain control steps in Digisonde 4D. 3:22. Automatic gain control in the Digisonde 4D is arranged prior to digitization to prevent A/D converters from under/over voltage conditions. At this stage of reception, the signal bandwidth continues to be large (varying for different operating bands of the tracking filters, but in the order of ~1 MHz) and therefore less sensitive to fast changes in characteristics of the individual interferers. For this reason, all Digisonde measurements are performed with a pre-determined table of the automatic gain settings, rather than with an optimal gain selection prior to each frequency transmission. 3:23. The autogain table shall be periodically refreshed, which is accomplished by running an ionogram measurement with “create gain table” option. Such ionogram starts with the process of table creation that takes varying time, depending on the number of frequencies and number of optimization steps needed on each frequency, usually in the order of 10-20 sec. If precise time synchronization of measurements to the round minute SECTION 3 OPERATING INSTRUCTIONS 3-13 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL is not important for the digisonde observations, then every ionogram can be configured to start with the gain table creation. However, it is quite acceptable to schedule gain creation to run only periodically, e.g., once a schedule. Such “gain table creation” ionogram can be configured to suppress output ionogram file (see Figure 3-7), so that the only outcome of its operation is refreshed gain table. NOTE If DCART scheduler does not detect “create gain table” programs in a schedule, it issues a warning to the operator. Such schedule is likely to run with non-optimal automatic gain settings. Figure 3-7: “Create gain table” program that refreshes the autogain table (ionogram file is not made). 3:24. It is recommended to switch digisonde to a lower constant gain setting during the night, when smaller absorption in the ionosphere results in stronger signals. NOTE It is important that “create gain table” measurement is configured to the same constant gain settings as the rest of measurement programs in the schedule. 3-14 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Programming Vertical Incidence Ionogram Measurement 3:25. The following data processing options shall be considered when programming the ionogram measurement: a. OUTPUT FILES: RSF versus SBF output format.  Default setting is RSF (Routine Scientific Format), ionogram with echo directions  SBF (Single Byte Format), for ionograms without echo directions, used for sustaining operations during periods of hardware faults in one or more receiver channels b. TWO-FREQUENCY PRECISION RANGING: enabled/disabled  Precision ranging is disabled by default.  Precision ranging is enabled by (a) setting number of fine steps to 2 and (b) selecting fine frequency step of 5 kHz. Then data from the second frequency are used to calculated precise range of echoes with 1 km resolution and then discarded. NOTE Ionograms with enabled two-frequency precision ranging take double time to complete.  Precision ranging mode requires RSF format for the output ionograms c. DATA REDUCTION: enabled/disabled  Data reduction is disabled by default.  For locations with a limited Internet bandwidth available for data delivery to the external data repositories, it may help to threshold data below the noise level (as determined by most probable amplitude, MPA) for a better file compression. d. RFIM: number of iterations  RF Interference Mitigation removes powerful narrowband interferers in the receiver bandwidth  Number of RFIM iterations is a system constant whose selection is influenced by available computing power of the DATA platform.  Higher number of iterations cleans a greater number of interferers but puts a greater load on the DATA computer.  When number of RFIM iterations is too high, DCART software starts buffering raw data to be processed, which may eventually cause memory shortage, depending on how buys is the overall measurement schedule. Monitoring state of DCART memory and thread information is possible using “Thread information and statistics” menu of DCART. RSF Ionogram with echo directions 3:26. Typical example of the RSF ionogram measurement program and corresponding ionogram display is shown in Figure 3-8. The concept for assigning colors to echo directions is explained in Section 1, Chapter 1. The insert in Figure 3-8 summarizes the mapping and provides direction codes used in the color legend. “No Value” color is used for signals whose direction of arrival could not be determined reliably. SECTION 3 OPERATING INSTRUCTIONS 3-15 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Color legend: Red shades = O-polarization, vertical Green shades = X-polarization, vertical Blue (cold) shades for North/East Yellow(warm) shades for South/West Figure 3-8: RSF ionogram with echo directions, running time ~2 minutes. 3-16 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL RSF Ionogram with echo directions and precision ranging 3:27. Precision ranging is enabled by (a) setting number of fine steps to 2 and (b) selecting fine frequency step of 5 kHz (Figure 3-9). Figure 3-9: RSF ionogram with echo directions and precision ranging, running time ~4 minutes. SECTION 3 OPERATING INSTRUCTIONS 3-17 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL SBF Ionogram without echo directions 3:28. Single Byte Format (SBF) is selected to make ionograms without echo directional analysis, which can be considered as a temporary operating mode for periods of hardware faults in one or more receiver channels. Figure 3-10: SBF ionogram without echo directions, antenna 3 disabled, running time ~2 minutes. 3:29. SBF ionogram mode can be also used as a reduced data volume solution for locations with a limited Internet bandwidth for data delivery. It is however recommended that the data reduction option is exercised first before resorting to the SBF ionogram mode, as the scientific value of SBF ionograms is inferior to the RSF ionogram mode with echo directions. Data Products Derived from Vertical Incidence Ionogram Measurement Automatic ionogram scaling with ARTIST 3:30. The Automatic Real-Time Ionogram Scaler with True height (ARTIST) is an intelligent system developed for extraction of ionospheric specification data from digisonde ionograms. The automatic ionogram interpretation (“scaling”) is a computer-hard problem that requires a model of human visual perception to extract useful ionogram image signatures and a syntactic analyzer to identify and characterize them. A common approach to the ionogram autoscaling in ARTIST is to (1) adaptively threshold the ionogram image to remove 3-18 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL background noise, (2) reduce echoes to edgels (edge elements) corresponding to the leading edge of the echo, (3) string echoes into traces, and (4) identify traces and determine their characteristics. 3:31. The ARTIST software reads ionogram file in RSF or SBF format and produces three types of output files for subsequent storage and dissemination: (1) complete set of scaled data in SAO 4.2 format, current digisonde network standard, (2) complete set of scaled data in SAOXML 5.0 format, expected new standard, and (3) set of MUF frequencies calculated for pre-configured path distances. All three types of the output files can be selected for local storage on the digisonde’s hard disk, archival on removable media (CD, DVD), as well as scheduled for delivery to remote servers via FTP or SFTP protocols, as further explained below in Chapter 4. 3:32. Figure 3-11 shows an example of ionogram picture prepared by Ion2PNG utility for the digisonde homepage, in which the raw ionogram data are combined with the ARTIST-derived ionospheric characteristics, NHPC-calculated profile of the electron density plasma, and table of the maximum usable frequencies (MUF) obtained for a pre-specified list of distances. The table of autoscaled characteristics include confidence level of the autoscaling ranging from 55 (low confidence) to 11 (high confidence), as well as the version of the ARTIST software used to obtain the scaled data. Color legend: Red shades = O-polarization, vertical Green shades = X-polarization, vertical Blue (cold) shades for North/East Yellow(warm) shades for South/West Figure 3-11: Ionogram display produced by Ion2PNG software for digisonde’s WWW homepage. Presentation of directional ionogram data as daily directogram 3:33. The directogram display is useful to view large-scale plasma irregularities as they drift across digisonde location. It uses RSF ionogram data to derive ground distances to the plasma structures responsible for the oblique echoes in the ionograms and then to plot them using direction, Doppler, and amplitude information of the echoes. The left panel of Figure 3-12 presents an example of the directogram plotted by Drg2PNG software using one day of RSF ionograms collected at Jicamarca, Peru. Each horizontal line of the directogram repre- SECTION 3 OPERATING INSTRUCTIONS 3-19 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL sents one ionogram measurement, with time going downwards. There are two vertical panels, with left panel corresponding echoes arriving from west, northwest and southwest, and right panel for echoes from east, northeast and southeast. The central line between the panels corresponds to the vertical reflection at zero zenith angle. The directogram on Figure 3-12 does not show much activity between 10:00 and 24:00 UT, at which time passing day-night terminator causes generation of several ionospheric disturbances traveling east. Shades of blue in the directogram correspond to general direction of plasma drift from west to east, and shades of red are used to represent drift in the opposite direction from east to west. Di = distance to reflection point i  = beam angle range = oblique echo Hv = representative height of the layer H i Figure 3-12: Daily directogram. (Left panel) sample directogram made by Drg2PNG software, (right panel) calculation of distance to the reflection point, Di 3:34. The right panel of Figure 3-12 illustrates calculation of the ground distance to the reflection point that is plotted along the x axis on directograms. Ground distance to the reflection point, Di, is calculated individually for each oblique echo range Hi corresponding to a plasma structure: Di  H 2 i  HV2 where Hv is a representative vertical height of the F layer that is estimated from the ionogram by locating the section of the vertical incidence F trace where amplitudes are high and height gradient is low. When manually scaled trace is available, hminF can be used reliably as Hv. For the autoscaled data, more consistent results are obtained by calculating summary amplitudes for each ionogram height and selecting Hv as the height of the highest summary amplitude. 3-20 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Programming Oblique Incidence Ionogram Measurement 3:35. Digisonde 4D can be configured to receive signals from other digisonde systems in the area, in which case transmitted signals arrive via oblique propagation mode (Figure 3-13). Both transmitting and receiving digisondes have to be synchronized to the UT time using their GPS receivers so as to start and progress the oblique incidence (OI) measurement in precise synchronization. In order for Digisonde 4D to transmit or receive signals in synch with DPS-4, it inserts additional pauses between individual CITs to replicate delays that DPS-4 requires to complete internal processing and data transfer. Such timing mode for oblique sounding is called “Oblique” (for reception from DPS-4) and “Compatible” (for transmission to DPS-4). Figure 3-13: Signal propagation during oblique incidence ionogram measurement between two digisondes. 3:36.    For a Digisonde 4D to receive oblique incidence signals, it is necessary to: Disable transmission of its own pulse (by selecting Radio Silent option), Select appropriate interpulse period to match transmitter mode, and Select transmitting Digisonde-4D or DPS-4 station from the list of stations1. o When a particular digisonde station is selected as transmitter, DCART automatically  calculates delay start of receiver sampling (start range) to skip the bottom ranges at which no signal can be observed, and  selects appropriate timing synchronization mode (Digisonde-4D or DPS-4). 1 When DCART starts up, it reads available station UDD files in its /UDD folder to discover all Digisonde-4D and DPS-4 station. The URSI codes of qualifying digisondes are then added to the drop-down menu of transmitters. SECTION 3 OPERATING INSTRUCTIONS 3-21 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL o It is possible to select UNKNOWN transmitter from the list to allow manual specification of the delay and synchronization mode. 3:37. Sample oblique incidence program specification is shown in Figure 3-14. There are two options for the interpulse period; 5 ms (1500 km range coverage) and 10 ms (3000 km). The sampling start delay is determined by two controls, (1) integer number of 5 ms periods (1500 km delay) to skip prior to starting sampling, (2) choice of the leading edge (0 km delay) or trailing edge (160 km delay) of the R pulse to trigger sampling. Figure 3-14: Digisonde 4D at Jeju Island, Korea, configured to receive signal from Anyang DPS-4 (444 km ground distance) via oblique propagation. Programming Drift Measurement 3:38. Sample drift measurement and real-time screen display of raw drift data are shown in Figure 3-15. As explained previously in Paragraph 3:9, 3:18, and 3:19, drift measurement is programmed to ensure high coherent integration time (CIT) and to reduce data volume by running a small number of fixed frequencies and output ranges. For the example shown in Figure 3-15,  the CIT is set at 20.48 seconds by using N of 128 (maximum supported by the DFT file format), 10 ms inter-pulse period, and 8x CIT increase by frequency multiplexing,  8 frequencies spaced by 50 kHz are used with the lower frequency limit set at the ARTISTrecommended value, and 3-22 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL  8 best ranges are picked for file storage by looking for the strongest echo in the interval of ranges between 140 and 500 km, which ensures that digisonde observes plasma drift in the F region. The real-time display shows data from 4 receiver channels (spectral amplitudes in the left panel, and phases in the right panel), selected at the best height out of 8 available as determined by the maximum signal strength. SECTION 3 OPERATING INSTRUCTIONS 3-23 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-15: Drift measurement program and real-time display. Data Products Derived from Drift Measurement Doppler skymap 3:39. The Doppler skymap is a presentation technique for the drift measurement data in which a large number of individual echoes from the ionosphere (“sources”) are resolved by their time of arrival and further by their Doppler shift that corresponds to the line-of-sight velocity of the reflecting area of plasma. Then, for each range/Doppler bin that is now assumed to contain a single ionospheric echo, four channel phases are used for the interferometry calculation of the azimuth and zenith angles of the source. DFT2Sky software is used to extract sources from the drift data for multiple frequencies and ranges and then save them in the SKY output file. SKY2PNG software is then used to plot sources as a skymap (Figure 3-16) where the azimuth and zenith angles of each source are used to place it on the skymap plane using a symbol whose shape and color indicate the Doppler velocity (positive Doppler uses + symbol and blue shades of color, negative Doppler uses o symbol and red shades of color). Further description of the skymap technique can be found in Section 1 of the manual, chapter “Drift Mode – Super-Resolution Direction Finding”. Bulk plasma drift velocity 3:40. The first order approach of describing plasma movement in the ionosphere is to assume its uniform drift over the station as a fixed 3D bulk pattern moving in the same direction with one velocity. In this case the off-vertical sources show the appropriate Doppler velocities (positive for the sources corresponding to the plasma drifting towards the station and negative for sources drifting away from the station). It turns out that such approximation works well in many situations, reflecting the large scale dynamics of the ionosphere at the sounder location. The bulk drift velocity is calculated using a least-squared fit to the skymap sources data in SKY files and output in DVL files. Daily plots of bulk drift velocities are produced for the digisondes webpage (see paragraph 3:43 below). Ionospheric tilt 3:41. Skymap sources can also be used to estimate local tilt of the ionosphere by calculating offset of the “gravity center” of skymap sources from the nadir. Zenith and azimuth angles of the local tilt are used to appropriately morph the 3D plasma distribution in the area surrounding the station, thus improving the accuracy of raytracing applications. TILT software is used to calculate zenith and azimuth angles and store them in .TLT file. Skymap display for WWW homepage 3:42. The skymap display (Figure 3-16) combines the skymap of ionospheric echoes calculated by the DFT2Sky software with bulk drift velocity obtained by DDAV software and ionospheric tilt parameters derived by the TILT software. The bulk Doppler velocity is shown in Figure 3-16 as the triple tick marks indicating the drift azimuth and horizontal velocity magnitude, as well as two labels that show the horizontal and vertical velocity components in m/s. The ionospheric tilt is described on the skymap display in terms of the zenith and azimuth angles of the source center. 3-24 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-16: Skymap display for WWW homepage. Daily velocity plot for WWW homepage 3:43. Daily plots of the ionospheric drift velocity are produced by DVL2PNG software for webpage publishing (see Figure 3-17). The plot shows 5 panels, with the top three panel showing three components of the velocity and bottom two panels showing ranges as frequencies of the skymap sources contributed to the calculation of the velocity. Programming Passive RF Sensing Measurements 3:44. In the passive ionospheric RF sensing mode, Digisonde 4D receives signals from remote transmitters of opportunity in order to infer characteristics of the ionospheric channel that received signals have traveled. Refer to Section 1 for further details on additional signal processing in the passive RF sensing mode. Figure 3-18 presents an example of Millstone Hill Digisonde 4D measurement of the EISCAT signal at 4040 kHz. SECTION 3 OPERATING INSTRUCTIONS 3-25 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-17: Daily drift velocity plot for WWW homepage. 3-26 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-18: Sample passive RF sensing measurement of EISCAT signal at 4040 kHz. 3:45. Figure 3-19 presents measurement program specification for the EISCAT signal reception data shown in Figure 3-18. The raw data are processed by averaging filter and saved in “generic” format with full 4 antenna data storage (.TAV files) for offline analysis in DCART. Figure 3-19: Fixed-frequency passive measurement of the EISCAT signal. SPECIFICATION OF RESTRICTED FREQUENCIES 3:46. DCART offers two separate lists of restricted frequency intervals (RFIL) where transmission shall be prohibited per site operating license, (1) for measurements with CIT ≤ 2 sec, (2) for measurements with CIT > 2 sec. Generally, this rule means that ionogram and drift measurements will be made with two different lists of restricted frequencies, so that swept-frequency ionogram measurement that stays on a particular frequency only for a short time and thus does not create much interference can have a less restrictive list. Drift measurements with CIT of 20 to 40 sec and multiple repetitions within several minutes of drift observations produce substantially greater EMI impact on radio systems, and their RFIL is expected to be more restrictive. SECTION 3 OPERATING INSTRUCTIONS 3-27 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 3:47. Both RFILs for low and high EMI impact are stored in StationSpecific.UDD file located in D:\Dispatch folder on DATA computer. Table 3-1 provides an example of RFIL specification for Millstone Hill observatory. Table 3-1. Specification of Restricted Frequency Interval List in StationSpecific.UDD configuration file %5 RESTRICTED FREQUENCY Restricted Frequency Table. Use format: Beginning-End Freq, (pairs define restricted bands) Restricted Frequency Table. Use format: Beginning-End Freq, (pairs define restricted bands) Remove asterisks to ignore restrictions Restricted frequency list for ionograms (code 946): --------------------------------------------------*946 < 2175-2195, 2850-3155 > *946 < 3400-3500 > *946 < 4000-4150, 4650-4750, 4985-5015 > *946 < 5450-5730 > *946 < 6200-6765 > *946 < 8355-8370, 8815-9040 > *946 < 9985-10015 > *946 < 11175-11400 > *946 < 13200-13410 > *946 < 14990-15100 > *946 < 17900-18030 > *946 < 19990-20010 > *946 < 21850-21870, 21924-22000 > *946 < 23200-23350 > *946 < 24990-25010 > *946 < 25550-25670 > Restricted frequency list for drifts (code 961): ------------------------------------------------ *961 < 1800-2000 > Amateur Radio Band *961 < 2175-2195, 2850-3155 > *961 < 3400-3500 > *961 < 3501-4000 > Amateur Radio Band *961 < 4001-4150, 4650-4750, 4985-5015 > *961 < 5450-5730 > *961 < 6200-6765 > *961 < 7000-7300 > Amateur Radio Band *961 < 8355-8370, 8815-9040 > *961 < 9985-10015 > *961 < 11175-13199 > frequency pairs cannot overlap each other *961 < 13200-13410 > *961 < 14000-14350 > Amateur Radio Band *961 < 14990-15100 > *961 < 17900-18030 > *961 < 18068-18168 > Amateur Radio Band *961 < 19990-20010 > *961 < 21000-21450 > Amateur Radio Band 3-28 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL *961 < 21850-21870, 21924-22000 > *961 < 23200-23350 > *961 < 24890-24990 > Amateur Radio Band *961 < 24991-25010 > *961 < 25550-25670 > HOUSEKEEPING MEASUREMENTS AND DATA PRODUCTS 3:48. In addition to the scientific measurements, digisonde conducts the following housekeeping activities: 1) Built-In Test (BIT) that determines state of the digisonde hardware health, including (a) Generation of data containing software test pattern, and (b) Generation of data containing hardware test pattern 2) Transmitter-receiver loopback measurements, including (a) Cross-channel equalizing (CCEQ) of receiver channels via internal loopback 3) Tracking filter calibration 3:49. BIT operation and data analysis is described in Section 6. Loopback and tracker calibration operations are described below in Chapter 4. Note that all housekeeping measurements produce data products:  BIT operation produces .BIT.XML files containing system health status reports,  CCEQ loopback operation generates .CEQ files and keeps the latest results in LATEST.CEQ file  Tracking calibration produces TRACKERS.DAT file for subsequent use in tracker configuration. COMMAND AND TELEMETRY TRAFFIC 3:50. The Digisonde 4D has two embedded computer platforms that exchange command and telemetry data over the Ethernet connection between them (Figure 3-20). SECTION 3 OPERATING INSTRUCTIONS 3-29 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-20: Digisonde 4D computer configuration with CONTROL and DATA platforms 3:51. The CONTROL platform is responsible for (1) measurement progression control in accordance with the program specification, (2) data acquisition, (3) packaging and delivery of the sample data to the DATA platform, (4) scheduling DPS-4D measurements, (5) synchronization to the GPS time reference, (6) responding to the user commands. The Control Platform operating software, Digisonde Embedded System Control (DESC), runs under the management of the real-time operating system “RTEMS” that ensures time-deterministic execution of the software tasks. 3:52. The Data Platform is responsible for (1) accepting raw data samples collected by the CONTROL Platform for processing, visualization, packaging in standard files, local backup to mass storage media, and delivery to external data recipients; (2) provision of the user interface for manual and unattended operations of the Digisonde 4D; (3) design of measurement programs, schedules, schedule switch planning rules, campaign requests; (4) commanding Digisonde 4D operations; and (5) publishing of the acquired science and housekeeping data to the digisonde homepage. 3-30 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 3:53. The dual platform configuration of the Digisonde 4D has a counterpart in space engineering applications where the CONTROL platform is a payload instrument onboard a satellite (without monitor and keyboard), and DATA platform is a ground systems console. With this analogy in mind, the traffic between CONTROL and DATA platforms is categorized as commands (from DATA to CONTROL) and telemetry (from CONTROL to DATA). The analogy with the space engineering applications is helpful in understanding that interactive editing of the digisonde configuration using at the DATA platform does not affect ongoing digisonde operations until new configuration is actually commanded (uploaded) to the CONTROL platform. 3:54. The Digisonde Commanding and Acquisition Remote Terminal (DCART) sends commands and collect telemetry data, processes raw sample data to create data products (ionograms, drift, and passive RF sensing records), and provides the user interface for manual and unattended operations of the Digisonde 4D. Chapter 2 and 3 of this Section describe DCART user interface in a greater detail. SECTION 3 OPERATING INSTRUCTIONS 3-31 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE CHAPTER 2 BASIC OPERATION OF DCART DIGISONDE 4D SYSTEM MANUAL BASIC PRINCIPLES 3:55. Digisonde Commanding and Acquisition Remote Terminal (DCART) is the software component of the Digisonde 4D sounder that is responsible for  interfacing the Control Platform to send commands and acquire telemetry data,  reducing collected raw data to data products (ionograms, drift and TAV records, etc.), and  providing the user interface for manual and autonomous operations of the Digisonde-4D, including: o design of measurement programs and schedules, o design of autonomous measurement plan, including routine and campaign periods, o manual operation of the instrument for science, engineering, and housekeeping tasks, and o real-time data visualization. 3:56. This Chapter describes user interface of the DCART software intended for basic operation of the Digisonde 4D in its manual and autonomous regimes. Advanced features of DCART interface are discussed in Chapter 3 of this Section. Design concepts and data interface of DCART software are described in Section 5. Normal and Advanced Modes of DCART Interface 3:57. Many of DCART functions are applicable to system development and troubleshooting tasks that are not needed during normal sounder operations. In order to reduce complexity of the user controls and associated screen clutter, DCART can be configured into the simplified interface mode, in which screen controls and data visualization panels are reduced to a minimum required for the basic sounder operations. Advanced interface mode and functions are described below in Chapter 3 of this Section. Figure 3-21 shows General Options panel where selection between Normal and Advanced interface modes is done. Figure 3-21: Configuring DCART in Normal Interface Mode (General Options) 3-32 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL DCART Screen Layout 3:58. Figure 3-22 describes general contents of the DCART screen. The bottom section contains DCART logo, real-time system clock (corresponding to both DATA and CONTROL computer clocks), DESC status window, and DCART log with software messages. The top section of the DCART screen has three operational state controls, Info button, and a drop-down menu with manual commands to CONTROL platform. The central section of the DCART window is taken by the tabbed panel whose contents depend on the selected content tab of the three available selections:  “PROGSCHD” with specification of programs, schedules, and SST planning rules,  “Sounding Mode” with visualization panel for sounding data, and  “Built-In Test” with visualization panel for BIT data. Figure 3-22: DCART screen layout (normal interface) SECTION 3 OPERATING INSTRUCTIONS 3-33 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL DCART Color Concept 3:59. Screen elements and controls of DCART software are color-coded to draw operator’s attention to particular conditions and selections:  RED  YELLOW  ORANGE  GREEN Error that requires operator’s action to resolve Notable/unusual item Important item affecting quality/amount of science data Recommended option for normal sounder operations Autonomous and Manual Digisonde Operations 3:60. The autonomy of sounder operations implies existence of planning rules that the instrument uses to execute particular measurements automatically. Complexity of the planning rules varies from simple specification of exact UT times for the planned measurements to intelligent algorithms that analyze external information to devise the measurement plan correspondingly. Once the planning rules are defined for the instrument, its continuing operation does not require further manual intervention. 3:61. Digisonde 4D implements its autonomous operation mode by triggering start of measurement schedules at particular UT times called Schedule Start Time (SST). In the autonomous mode, the CONTROL platform of Digisonde 4D repeatedly checks contents of its SST Queue to start the earliest schedule in the queue when its SST matches system clock time. It is responsibility of the DCART software to replenish SST Queue with new items as SSTs expire. See Paragraphs 3:4 and 3:5 in this Section for a more detailed description of the schedule, SST, and SST Queue. 3:62. Manual Digisonde 4D operation means that particular measurement program or schedule is triggered by manually sending the Start command to CONTROL platform. In the manual operation mode, SST Queue content is ignored. CAUTION THE OPERATOR SHALL NOT LEAVE THE SOUNDER OBSERVATORY WITH DIGISONDE IDLING OR RUNNING IN THE MANUAL MODE. IT IS IMPORTANT TO LEARN HOW TO DISTINQUISH WHETHER DIGISONDE IS IN ITS AUTONOMOUS OR MANUAL MODE. IN THE MANUAL MODE, AUTOMATED SST PLANNING RULES ARE IGNORED, EVEN IF THE SOUNDER APPEARS TO BE COLLECTING DATA FROM A RUNNING SCHEDULE. 3:63. Figure 3-23 shows section of DCART main window with the DESC state (bottom part of the Figure) indicated as (a) Manual and (b) Automatic. In both modes shown in Figure 3-23, digisonde is running Program #1 of Schedule #2. However, in the manual mode of operations (the left panel of Figure 3-23), DESC will continue running schedule #2 indefinitely (or until the system is manually commanded into different schedule or state). In the Autonomous mode (the right panel of Figure 3-23), sounder will be switching measurement schedules automatically per SST planning rules. 3:64. In order to switch Digisonde 4D into its Autonomous mode, push Auto button (see Figure 3-23). There are two ways to stop autonomous operations and switch the sounder to its manual mode: 3-34 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL  STOP – stop current measurement immediately (data product file will be truncated), and  Soft STOP – let currently running program to complete before switching into manual mode (a) Digisonde in the Manual Mode (b) Digisonde in the Autonomous Mode Figure 3-23: Digisonde in its (a) Manual and (b) Autonomous modes of operation. Push “Auto” button to switch to the Autonomous mode. Push STOP or Soft STOP to switch to the manual mode. 3:65. When Digisonde 4D is commanded into Autonomous Operations mode,  DESC is switched into its automatic state (i.e., it triggers schedules in its SST Queue), SECTION 3 OPERATING INSTRUCTIONS 3-35 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL  DCART uses its SST planning rules to automatically replenish SST Queue of the DESC. 3:66. When DCART is in the Autonomous mode of operations, several screen controls and menu options are disabled until DCART returns to the manual mode:  DCART window cannot be closed,  Manual start of schedules and programs is disabled,  Auto button is disabled,  Management of external PROGSCHD files is limited PROGSCHD Management 3:67. “PROGSCHD” \prōg-skĕd’\ is a nickname for the data structure that holds all measurement configuration data pertaining to Digisonde 4D programs, schedules, schedule start times (SSTs), and SST planning rules and campaign requests. The heritage of the name PROGSCHD can be traced to the times when Microsoft DOS operating system used by DPS had an 8 symbol limit for the filenames. Active and Edited PROGSCHD 3:68. Figure 3-24 illustrates management of the PROGSCHD data structures by DESC and DCART components of the operating software. It is important to understand that, at all times, it is CONTROL platform that conducts digisonde measurements using the active PROGSCHD specification that resides in its operating memory. Digisonde operator has access only to PROGSCHD structures that are stored in DATA platform. Figure 3-24: Management of PROGSCHD structures by DESC and DCART software. 3:69. DCART software has screen editors for all components of PROGSCHD structure. It has two copies of PROGSCHD in its memory available for display in the editors, (1) active PROGSCHD that can be only viewed 3-36 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL but not modified, and (2) edited PROGSCHD that can be modified using editor controls. DCART allows single-click switch between active and edited copies of PROGSCHD (see Figure 3-25). The active copy of PROGSCHD is displayed grayed-out to indicate that it is impossible to edit it. (a) Active PROGSCHD shown in the editor (b) Edited PROGSCHD shown in the editor Figure 3-25: Display of the (a) active and (b) edited PROGSCHD in DCART. NOTE Program and schedule definitions displayed on the Digisonde 4D screen may not correspond to the measurements that CONTROL platform of the sounder is actually running -- if DCART shows the edited PROGSCHD with changes that have not been activated. PROGSCHD Activation 3:70. Operator-introduced changes to PROGSCHD that is currently visible in DCART editors have to be activated in order for the sounder to starting using them in new measurements. “Activate changes” button above the system clock display in Figure 3-25 is used for PROGSCHD activation. As illustrated in Figure 3-26, when “Activate changes” button is pressed, the following actions are taken:  Edited PROGSCHD is validated (tested for possible programming errors),  Program definitions, Schedule definitions, and current SST Queue from the Edited PROGSCHD are copied to CONTROL platform using DCART-DESC commanding protocol, SECTION 3 OPERATING INSTRUCTIONS 3-37 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL  Full specifications of the Edited PROGSCHD are copied over to active PROGSCHD copy in DCART, and  Full specifications of the Edited PROGSCHD are saved in the Active PROGSCHD file in DCART folder (for resuming operations in case of a system reset). Figure 3-26: Activation of the edited PROGSCHD. 3:71. Activation of the Edited PROGSCHD can be done while the sounder is in the Autonomous mode of operations and currently runs a measurement. When “Activate changes” button is pressed and sounder is running, DCART:  commands DESC into manual state using “Soft STOP” command (display of the DESC state changes o the screen accordingly),  waits until DESC completes currently running measurement, if any,  commands CONTROL platform in “Standby” state for configuration updates,  uploads new PROGSCHD definitions, and  returns CONTROL platform into automatic state to resume scheduled operations. Offline PROGSCHD editing 3:72. DCART can be used for offline editing of PROGSCHD definitions stored as files on DATA computer. Such files can be opened for reading, editing in DCART, and writing back to the hard disk. Figure 3-27 illustrates the process of offline PROGSCHD editing using File menu of DCART. 3-38 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-27: Offline editing of external PROGSCHD files on DATA platform. 3:73.   The File menu also contains: “New PROGSCHD” item that will initialize Edited PROGSCHD to an empty structure, and “Open Active PROGSCHD” item that will re-read Active PROGSCHD definitions from the external storage to make sure that Edited PROGSCHD displays the Active PROGSCHD and not some other PROGSCHD file. REAL-TIME DATA VISUALIZATION 3:74. Two of the content tabs in Figure 3-22 are used for real-time visualization of science (“Sounding Mode”) and housekeeping (“Built-In Test”) data. NOTE Real-time data visualization is a task that requires substantial resources of the DATA platform. The real-time displays have to be disabled before leaving the sounder working in the autonomous mode. 3:75. Figure 3-28 shows the “Sounding Mode” real-time display of DCART in its disabled state. Push button “Enable Data Display” to start visualization. When the real-time display is no longer needed, disable it by pushing “Suspend Data Display”. In the Suspended state of the real-time visualization, the latest sounding mode data will be preserved on the screen. 3:76. The real-time and offline data displays of DCART have capability of showing intermediate steps of data processing, as long as the source data are not completely processed. Figure 3-29 shows the “Sounding Mode” real-time display showing ionogram measurement in progress, with Display Option window invoked by pushing “Display Options” button. The Display Option window shows Processing Chain, a list of processing steps that DCART applies to the source data (in this case raw time domain data stream from DESC). Radio buttons are available to select final or intermediate steps of the processing chain. SECTION 3 OPERATING INSTRUCTIONS 3-39 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-28: Real-time “Sounding Mode” display of DCART (disabled). 3-40 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-29: Real-time “Sounding Mode” display of DCART (enabled). DCART Processing Chain 3:77. Detailed description of the processing steps that are applied to Digisonde 4D time domain samples can be found in Section 1. Table 3-2 summarizes contents of the full Processing Chain in DCART. Steps 1-4 are performed in the time domain for 4 antenna channels individually. Doppler analysis (step 5) is applied to sample sets collected across multiple repetitions of pulses at the same frequency for the same range bin. Reduction to ionogram (step 6) is done for ionogram mode only by selecting only one Doppler line from the 4 channels of spectra for each range bin, and calculating direction of echo arrival for selected Doppler line only. Different types of real-time display are provided in DCART for steps 1-4, 5, and 6. Table 3-2. DCART Processing Chain # Step Contents 1 RFI Mitigation 2 Cross-channel Equalizing (CCEQ) 3 Pulse Compression 4 Sum of complementary codes 5 Doppler spectral analysis 6 Reduction to ionogram optional optional Comments max Doppler/beam, for ionogram mode only Real-time Display of Time-Domain Data (steps 1-4 of Processing Chain) 3:78. Figure 3-30 shows real-time Time Domain display (labeled TIME DOMAIN in the background) showing four channels of data with magnitude of signal in the left column and phase in the right column. The plot shows measurement of the internal loopback signal from the transmitter card to the antenna switch; phase plots clearly display the 16-chip phase code of the signal modulation. Available screen controls for data visualization are shown in Table 3-5. Table 3-3. Display options for Time-Domain real-time window Location Top Bar Control “dB scale” checkbox “Re/Im - Mag/Ph” radio buttons “Time domain - Freq domain” radio buttons “Phase difference” checkbox “Min amplitude to show phase” text field Function represent amplitudes in dB scale or 16-bit linear scale Cartesian (Real and Imaginary) versus Polar (Magnitude and Phase) representation of the sample data Time domain data are raw samples, frequency domain data are produced by applying DFT to [unsorted] time domain samples Option to subtract phase of channel 1 from all channels2 Threshold value of magnitude below which phase values are not plotted (to reduce clutter)2 2 Screen control is disabled when Magnitude/Phase representation is not used. SECTION 3 OPERATING INSTRUCTIONS 3-41 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Location Control “Export” button “Tabulated export” checkbox Function Produce text file with sample data for one look of measurements Option of the text file export to add tabs Left zoom panel “Use Zoom” checkbox “Min hgt, km” and “Max hgt, km” text fields “Alt colors” checkbox Enable/disable zooming Min/max height values for zoomed display Option to use alternative colors for neighboring values to facilitate counting of values Figure 3-30: Real-time “Sounding Mode” display, Time Domain plot (steps 1-4 of the Processing Chain). Real-time Display of Doppler Spectra (step 5 of Processing Chain) 3:79. Figure 3-31 shows real-time “single range” Doppler Spectra display, in which FFT is taken over sorted samples belonging to the same range bin across pulse repetitions. The plot shows four channels of data with the 3-42 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL magnitude of signal in the left column and phase in the right column. Note that abscissa of the plots uses Doppler Frequency in Hz. Available screen controls for data visualization are shown in Table 3-4. Figure 3-31: Real-time “Sounding Mode” display, Doppler Spectra plot (step 5 of the Processing Chain). Table 3-4. Display options for Doppler Spectra real-time window Location Top Bar Control “dB scale” checkbox “Adjust to max amp” checkbox “Pref” button “O/X Pol” toggle button “Auto Height” checkbox “Height” text field “No of heights” text field Function Represent amplitudes in dB scale or linear scale Adjust the Y axis to fit maximum amplitude across 4 channels Open options window to select Doppler image preferences, see Figure 3-32 and explanations below Select O or X polarization for display Option to pick height for display at which signal is the strongest, or specific “Height” index for display Height index for display if not in AutoHeight mode Number of height in the waterfall representation (see Figure 3-32 for selection of the waterfall representation) SECTION 3 OPERATING INSTRUCTIONS 3-43 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Location Control Refresh rate spinner field Function Refresh rate of the screen in ms 3:80. Doppler Image Options window (Figure 3-32) has a number of options for display of the Doppler spectra in the real-time window of DCART. The window layout and contents is re-used from the UMLCAR Drift Explorer project libraries, and certain options are not applicable to the real-time visualization. Figure 3-32: Doppler Image options for the real-time Doppler Spectra plot Table 3-5. Display options for Doppler Image Category Control Function Data Presentation “Linear scale” checkbox “Single range” or “Waterfall” presentation Represent amplitudes in dB scale or linear scale Presentation as single range (Figure 3-31) or waterfall (Figure 3-33) Processing “Global MPA” checkbox “Threshold” text field Use amplitude thresholding, display amplitudes above threshold in black Threshold value above MPA Visual utes Attrib- “Printer color scheme” checkbox “Show title” checkbox Use black on white background (printer) versus white on black background (screen) display Show standard preface information as title 3-44 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Category Control “Show local time” checkbox “Local Time types” combobox “Show interior plot annotation” checkbox “Foreground interior plot annotation” checkbox “Show infoline” checkbox “Show logotype” checkbox Function Show additional line in the title with local time Type of LT for displays of local time Add Amplitude/Phase labels to the plot background Bring plot annotations to the foreground N/A Show Digisonde logo in the upper left corner Crosshair Line “Show instant values” checkbox “Show cross-hair Doppler line” checkbox Add a side window to display values at the crosshair position Add cross-hair line to spectra plots Browsing controls Browsing and spanning modes Picture options Picture format options N/A to real-time display N/A to real-time display Waterfall presentation of the drift data 3:81. In Doppler Image Options window, set “Presentation” drop-down menu to “Waterfall” to obtain waterfall display (see Figure 3-33). SECTION 3 OPERATING INSTRUCTIONS 3-45 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-33: Waterfall display of drift data in real-time. Real-time Display of Ionograms (step 6 of Processing Chain) 3:82. Figure 3-34 shows a typical display of ionogram measurement in progress using the ionogram presentation, in which colors are used to represent echo status (polarization, Doppler shift, and angle of arrival). Available options allow to change thresholding parameter, select polarization channel for display, zoom the image to particular ionogram section, and use printer or screen color scheme. Figure 3-34: Real-time display of ionogram measurement in progress, ionogram presentation. 3:83. Ionogram measurement can be additionally presented as an echogram, in which color is used to represent signal amplitude (see Figure 3-35). In addition to the common options for the ionogram visualization, the echogram display allows selecting individual antennas, assigning different maximum amplitude value to the color legend, and presentation of the data as spectrogram (see discussion below). 3-46 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-35: Real-time display of ionogram measurement in progress, echogram presentation. 3:84. “Show as spectrogram” checkbox of the echogram display allows presentation of the ionogram data in the frequency surveillance style as shown in Figure 3-36. It is possible to select maximum, minimum, median, or spectral maximum amplitude out of all available data per frequency for plotting on the spectrogram. In addition to the frequency surveillance at the sounder location, spectrogram presentation can be useful for tracker calibration, evaluation of the receiver transfer function, and monitoring of the system noise floor. Figure 3-36: Echogram presentation of the same ionogram as in Figure 3-35, shown as spectrogram. Real-time Display of BIT results 3:85. Figure 3-37 shows example of a failed Built-In Test display. Further recommendations for using BIT in system troubleshooting, with relevant displays and in-depth analysis, can be found in Section 6 of this Manual. SECTION 3 OPERATING INSTRUCTIONS 3-47 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-37: Real-time BIT display. OFFLINE DATA VISUALIZATION 3:86. DCART provides additional display capabilities for offline visualization of data previously saved in output files. The offline display selections can be found in Action menu of DCART. All viewing actions of DCART open a separate window with similar displays as in the real-time visualization of data from CONTROL platform, with additional controls for opening file and browsing its contents. AUTONOMOUS OPERATIONS OF DIGISONDE 4D 3:87. In order to configure Digisonde 4D for autonomous operations, it is necessary to complete the following tasks: 1) Prepare measurement program specifications 2) Assemble programs in schedules 3) Design planning rules for schedule switching within one day 4) Add campaign requests if needed 5) Switch the sounder into autonomous mode 3:88. It is recommended to have different schedules for routine daytime and nighttime operations, and for campaign periods:  DAYTIME ionogram measurements should have wider frequency coverage, coarser frequency resolution, and higher receiver gain.  NIGHTTIME ionogram measurements should have smaller frequency coverage, finer frequency resolution, and lower receiver gain to accommodate stronger returns from ionosphere when no D region absorption occurs.  CAMPAIGN periods usually require higher cadence of measurements. 3-48 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Basic Schedule Editing with DCART 3:89. Once started, schedule repeats measurement programs that are included in its specification. In order to arrange 15 minute cadence of Digisonde 4D measurements (4 times an hour), it is sufficient to define 15 minute schedule. If a schedule has to combine operations of different cadences, its duration shall match the least frequent cadence. For example, if 15 minute ionogram measurements have to be combined with an hourly passive sensing observation, 1 hour schedule is needed with 4 copies of ionogram measurement and one passive operation. Refer to Chapter 1 of this Section, Para 3:2 and onward, for review of programs and schedules. 3:90. DCART Schedule Editor panel is used to assemble programs in schedules. Figure 3-38 shows a sample schedule #17 that takes ionograms every 15 minutes. Left column of DCART screen is taken by the list of available schedules. Central panel is taken by two Schedule editor components, Program List (upper section) and Schedule Image (lower section). Schedule #17 has fixed length of 15 minutes and, in addition to the daytime ionogram measurement program #8 at the schedule start, it also contains three additional support programs: Built-In Test program #11 to evaluate system health status, Cross-Channel Equalizing program #25 to calculate compensations for inequalities in 4 receiver channels, and CreateGainTable program #27 to refresh the autogain table (see discussion in Para 3:23 and Figure 3-7). The ionogram measurement is placed at the schedule start so that ionograms are coincident with the SST plus integer multiples of 15 minutes. The autogain program is placed at the end of the schedule to evaluate current noise environment as close to the ionogram start as possible. Placement of the BIT and CCEQ programs within the available idle time of this schedule is arbitrary. Figure 3-38: Example of 15 minute ionogram schedule NOTE SECTION 3 OPERATING INSTRUCTIONS 3-49 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL It is recommended to include in each schedule one BIT program, one CCEQ program covering appropriate frequency range, and one ‘Create Gain Table’ program with appropriate constant gain. 3:91. Upper controls of the Program List panel, “Add”, “Delete”, “Insert” and “Clone”, are used to modify schedule contents. 3:92. Figure 3-39 shows a commonly used daytime Digisonde schedule that includes two skymap measurements for E and F region and increases cadence of measurements to 8/hour. 3:93. “Idle” checkbox is used to create an empty schedule. The empty schedule can be useful for adding periods of radio silence to the measurement plan. If an unplanned radio silence of the Digisonde is needed, it is best accomplished by switched it into Manual Operations state. Figure 3-39: Typical example of 7.5 minute ionogram schedule NOTE For routine scientific observations of the ionosphere it is recommended to keep Digisonde at 5 or 7.5 min cadence to ensure sufficient coverage of occasional periods of elevated ionospheric activities such as geomagnetic storms. It is also important to have the radar range set at 1500 km (10 ms inter-pulse period) for ionogram and drift programs to capture dynamics of ascending ionosphere during the storm activities. 3-50 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Advanced Schedule Editing with DCART 3:94. The “Auto” checkbox of the Schedule Editor switches the editor into the automatic placement mode (Figure 3-40) in which gaps between scheduled programs are forced to a fixed value (1000 ms for the example shown in Figure 3-40), and schedule duration can be padded to a needed value by entering appropriate “last” gap value (2000 ms for the example shown in Figure 3-40). “Adjust” button is used to enforce automatic placement rules on all programs in the schedule. “Between” and “last” buttons are used to make adjustments to individual parts of the schedule. Manual Placement mode: Automatic Placement mode: Figure 3-40: Manual and Automatic placement modes of the Schedule Editor 3:95. ASAP (as soon as possible) modifier replaces fixed offset and duration times of the schedule with instruction to the DESC software to start next program as soon as current program completes. The ASAP modifier brings uncertainty of the actual program start time because the time is not synchronized to the computer clock anymore. Although CONTROL platform warrants deterministic execution of the programs, their actual duration can still be affected by unaccounted events in the system. The ASAP modifier is used to start programs whose absolute timing is not required within the schedule duration period (e.g., skymaps, CCEQ, autogain programs). The ASAP modifier can also be placed on the schedule duration itself, which may be useful for continuous observations without absolute timing of their start (as in space applications, for example). Programming SSTs with Planning Rules and Campaign Requests 3:96. Calculation of new Schedule Start Times (SST) is needed for appropriate switching of digisonde schedules within a day (e.g., daytime and nighttime) or in support of joint observational campaigns with other instruments. There are two distinct mechanisms for calculation of SSTs working in conjunction:  RULES: algorithms to appropriately start schedules within one day  CAMPAIGNS: specification of UT periods (start and stop times) to override the rule-calculated SSTs 3:97. Figure 3-41 shows SST Editor panel of DCART. The upper section of SST Editor has Status bar and two tables with rules and campaigns, and the lower section displays Timeline window with optional SST Table. The Timeline window has Timeline Image with zoom-in controls and option selectors. Timeline example in SECTION 3 OPERATING INSTRUCTIONS 3-51 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-41 shows 1 hour of Digisonde operations from 2009.01.26 02:00UT to 2009.01.26 03:00UT, during which daytime schedule #2 is switched to nighttime schedule #3, at 2:45 UT. NOTE Timeline image may not show individual programs if selected timeline interval is too large for a detailed view of the schedule structure. Use Programs and Schedules text fields in the Timeline panel to specify the threshold at which detailed view is no longer provided because of screen clutter. Figure 3-41: SST Editor Planning Rules 3:98. One Planning Rule contains (a) Schedule Number and (b) Condition that can be one of three kinds:  START CONDITION for the schedule to start,  INTERVAL CONDITION for the schedule to start and finish, or  DEFAULT CONDITION for the schedule to run when no other conditions apply. 3:99.     Rule conditions can be written as simple formulas that use UT time of the day (keywords StartUT and RangeUT) specified in hh:mm:ss.sss format Daylight time in the F region (keyword Day and its boundaries Day.Start and Day.End) Nighttime in the F region (keyword Night and its boundaries Night.Start and Night.End) Offset from condition one row higher in the table (keyword Offset) 3-52 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 3:100. Condition formulas can modify the keyword or its boundaries by adding or subtracting time deltas. For example, to start a schedule 30 minutes before daylight time in the F region, condition Day.Start-30m is used in the rule. Time deltas can be specified as negative or positive times in hours, minutes, seconds, milliseconds, or in schedule iterations (units of schedule duration):  Time Delta Format 1 (time):  Time Delta Format 2 (time):  Time Delta Format 3 (schedule iterations): [-,+] [Nh] [Km] [Ls] [Mms] [-,+] L.Ms Ii START CONDITIONS 3:101. Table 3-6 enlists types of start conditions, in which the schedule starts at the specified time and runs until another rule condition becomes effective. Table 3-6. Start Conditions Keyword StartUT StartUT 10 StartUT 10:20 StartUT 10:20:00.250 Day.Start Day.Start Day.Start-30m Day.End Night.Start Night.Start Night.Start+1h Night.End Offset Offset 1h Offset 10i Example Start schedule at 10:00UT Start schedule at 10:20UT Start schedule at 10:20:00.250UT Start schedule at day start Start schedule 30 minutes prior to day start Start schedule at night start Start schedule 1 hour after night start Start this schedule after 1 hour of previous schedule operations Start this schedule after 10 iterations of previous schedule Usage Notes Analogous to DPS-4 stock scheduler 10 ms resolution Calculated individually for all locations and days of year Refer to foF2 daily plot to select optimal day/night switch Night.Start is preferred for clarity Calculated individually for all locations and days of year Refer to foF2 daily plot to select optimal day/night switch Day.Start is preferred for clarity Useful for testing INTERVAL CONDITIONS 3:102. Table 3-7 enlists types of interval conditions, in which the schedule starts and finishes at the specified times. When the schedule finishes, SST planning algorithm reviews other rules to decide which schedule to run next. SECTION 3 OPERATING INSTRUCTIONS 3-53 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Table 3-7. Interval Conditions Keyword RangeUT RangeUT(10,20) RangeUT(10,10:30) Day Day Day(-30m, +1h) Night Night Night(+1h, -30m) Offset Offset(10m, 30m) Offset(10i, 20i) Example Run schedule from 10:00 to 20:00UT Run schedule from 10:00 to 10:30UT Usage Notes 10 ms resolution Run schedule during daytime Start schedule 30 minutes prior to day start, finish schedule 1 hour past day end Calculated individually for all locations and days of year Refer to foF2 daily plot to select optimal day/night switch Run schedule during nighttime Same as Day(-30m, +1h) Calculated individually for all locations and days of year Refer to foF2 daily plot to select optimal day/night switch Start schedule 10 min after previous condition in the list, stop after 30 min of operation Start schedule after 10 iterations of previous schedule and run 20 iterations of current schedule NOTE Start times suggested by planning rules that use Day and Night conditions, as well as their boundaries Start and End, are subject to “Snap to UT grid” analysis that shifts the start time to the nearest end of previous schedule iteration, so that the SST planner does not interrupt schedules in the middle. COMBINING PLANNING RULES IN THE RULES TABLE 3:103. The Rule Table can have multiple rules with start and interval conditions, and one default rule. As a minimum, the Rule Table has to have one default rule, in which case no schedule switching is occurring, and the sounder remains in the schedule specified in the default rule indefinitely. 3:104. When more than one planning rule is specified in the Rule Table, DCART planning algorithm parses the rules to calculate SSTs within the day period. It is possible that more than one condition applies to the same period of time of day, in which case planning algorithm considers rule priority (rule placed higher in the Rule Table has higher priority). The planning algorithm concepts can be summarized as follows:  Schedule with a start condition finishes as soon as another condition starts.  Schedule does not start if another schedule is running with a higher priority interval condition.  When schedule with interval condition finishes, new running schedule is selected as the highest priority schedule applicable.  Default schedule has lowest priority. 3-54 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 3:105. Table provides two examples of priority analysis. Table 3-8. Examples of priority analysis # Rule Table Example 1 RangeUT(10,20) for Schedule #1 RangeUT(14,22) for Schedule #2 Default Schedule #3 2 RangeUT(14,22) for Schedule #2 RangeUT(10,20) for Schedule #1 Default Schedule #3 Action Run #1 from 10 to 20 UT, run #2 from 20 to 22UT, run #3 from 22 to 10 UT Run #1 from 10 to 14 UT, run #2 from 14 to 22UT, run #3 from 22 to 10 UT Campaign Requests 3:106. One Campaign Request contains (a) Schedule Number, (b) Start UT, and (c) End UT for the schedule to run. The campaign request overrides existing SST sequence generated using planning rules. In addition to the campaign requests typed into Campaign Table manually, DCART can accept external standard .RCR files (Remote Campaign Request) to handle copious schedule switches that may be needed, for example, to support daily spacecraft overpasses. The RCR files can be generated automatically by ADRES subsystem of the DIDBase repository using data from orbit propagators. Real-time Display of Schedule Progression in SST Editor 3:107. Enabling “Real-Time” checkbox in DCART Timeline window switches it to display of schedule progression using current system clock time as the Timeline start and setting the Timeline end to a window of configurable length (see Figure 3-42). SECTION 3 OPERATING INSTRUCTIONS 3-55 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 3-42: Real-time Timeline display of schedule progression. MANUAL OPERATIONS OF DIGISONDE 4D 3:108. Manual operation of the sounder may be needed as a part of its testing, troubleshooting, or during development of new science programs and schedules. NOTE Development of new programs, schedules, and SST planning rules can be done without interrupting ongoing sounder operations using DCART console of the sounder. Note that physical presence at the sounder site is not required for PROGSCHD editing. Refer to “Remote operations” Chapter of this Section for further information, including use of a stand-alone version of DCART installed on another (remote) computer for offline editing. 3:109. Use “Soft STOP” command to switch sounder into its Manual Operations mode. Once in the manual mode, use Prog and Schd tabs for manual start of programs and schedules. 3:110. When developing new programs or schedules, it is not necessary to always activate changes (using Activate changes” button of the PROGSCHD tab). It is sufficient to run new program or schedule manually using “Run Selected Program” of Program List or “Run Selected Schedule” of the Schedule List (see Figure 3-43). Manual runs of a program or a schedule includes upload of its new definition to CONTROL platform, but does not overwrite local copies of active PROGSCHD in DCART memory and on the hard disk. Once development is completed, the changes may be activated or discarded. To discard introduced changes, load the active PROGSCHD the disk using File – Open Active PROGSCHD and then activate it so that it completely refreshes DESC and DCART definitions. 3-56 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL (a) Manual Mode, running program #1 (b) Manual Mode, running schedule #11 Figure 3-43: Digisonde in its Manual Operations mode, running (a) program #1 and (b) Schedule #11. 3:111. Commonly used keyboard shortcuts for the manual program runs: F9 Run selected program F10 Stop SECTION 3 OPERATING INSTRUCTIONS 3-57 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL CHAPTER 3 DIGISONDE 4D PROGRAMMING RECOMMENDATIONS QUALITY CONTROL OF PROGSCHD DEFINITIONS 3:112. DCART editors have a comprehensive built-in system of quality control that makes it difficult to program Digisonde 4D measurements erroneously. If a program or schedule design violates any of the included quality checks, the editor places red-colored “Show Design Error” button on the top panel of the editor and generates a warning window if operator navigates away from the definition that raised the error flag. Pressing the “Show Design Error” button opens a report window with explanation of the error condition. 3:113. Typical classes of errors that DCART editors identify automatically to raise the error flag are:  PROGRAM SETTINGS INCOMPATIBLE WITH OUTPUT DATA FORMAT o use of RSF/SBF ionogram format with frequency stepping other than linear, o use of DFT drift format with N above 128, o etc.  INCOMPATIBLE SETTINGS WITHIN ONE PROGRAM o sampling beyond the boundary of next repetition period, o incorrect placement of fine steps within the coarse step, o use of directional analysis when antenna array is incomplete, o etc.  SCHEDULES WITH OVERLAPPING PROGRAMS  MISSING GAIN EVALUATION o all programs in the schedule use autogain table, but no program evaluates it  etc. VALID PROGRAMS UNSUITABLE FOR SCIENCE OBSERVATIONS 3:114. There are several kinds of valid measurement programs that do not result in valid science data:  Programs with 0 km start range  Programs with “loopback” option instead of “measurement”  Programs with “HW pattern” or “SW pattern” option instead of “measurement”  Programs with “Save Product File” option disabled VALID PROGRAMS WITH POTENTIAL PROBLEMS 3:115. Measurement programs that capture raw data stream in output files (program option “Save raw file” or top level option “Save all raw data”) have potential implication of overfilling the hard disk of DATA platform. 3:116. “Radio Silent” option may not be intended for ionogram measurement, unless it is oblique sounding experiment. VALID PROGRAMS SUBOPTIMAL FOR SCIENCE OBSERVATIONS 3-58 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Ionogram measurement 3:117. Program design recommendations for the ionogram measurements are summarized in Table 3-9. Table 3-9. Program design recommendations for ionogram measurements # Recommendation Motivation 1 Use beam-forming analysis to Echo directions help interpretation calculate echo directions of ionograms, both manual and unless malfunction of the re- automatic by ARTIST ceiver channel(s) is suspected 2 Use precision ranging option Precision ranging removes range bias, improves resolution, and ultimately helps automatic interpretation by ARTIST 3 Use 10 ms inter-pulse period for 1500 km radar range 4 Use appropriate frequency resolution of 50 or 25 kHz Provides capability of recording ionospheric uplift during periods of storm activity. Ionograms with 750 km radar range miss important ionospheric information. ARTIST performance improves with better frequency resolution. 5 Watch for fxF2 exceeding the Avoid truncated ionograms upper limit of ionogram Usage Implications State of hardware health, channel equalization, and antenna array placement shall be adequate to use phase-aware techniques to calculate directions Dual-frequency analysis for precision ranging doubles the ionogram running time and may require coarser frequencys stepping, lowering on the N (number of integrate pulses) or the upper frequency limit. Setting 10 instead of 5 ms IPP doubles the ionogram running time and may require time reduction measures (see usage implications for recommendation 2). Smaller frequency step means longer running time, which may require time reduction measures (see usage implications for recommendation 2). Ionograms with higher upper limit run longer and may require adjustments to the schedules that use them. Drift measurement Program design recommendations for the drift (Doppler skymap) measurements are summarized in 3:118. Table 3-10. Table 3-10. Program design recommendations for drift measurements SECTION 3 OPERATING INSTRUCTIONS 3-59 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL # Recommendation 1 Set CIT time to 20 (day) or 40 seconds (night) by using appropriate inter-pulse pe- riod, number of pulses per frequency, and frequency multiplexing. Motivation Improved Doppler resolution for a better signal analysis and echo resolution in skymaps Usage Implications Higher EMI on radio systems, longer minimum running time. Doppler frequency bandwidth at 40 sec CIT may not be sufficient for polar locations. General recommendations for program design 3:119. General program design recommendations are given in Table 3-11. Table 3-11. General program design recommendations # Recommendation Motivation 1 Watch for signs of receiver Saturation effects affect quality of saturation and adjust constant phase measurements, noise floor, gain accordingly. and signal to noise performance of the sounder. Usage Implications None. Use the following saturation indicators: red saturation flag in the raw data display and saturation conditions in the BIT. VALID SCHEDULES SUBOPTIMAL FOR SCIENCE OBSERVATIONS 3:120. The following deficiencies of schedule designs are not reported automatically:  No loopback CCEQ program is included,  No BIT program is included,  Gain evaluation program uses constant gain setting different from subsequent science programs, and  CCEQ or Gain evaluation program use incompatible frequency range and step with subsequent science programs. GENERAL RECOMMENDATIONS FOR DIGISONDE OPERATIONS 3:121. General recommendations for Digsionde 4D operations are summarized in Table 3-12. Table 3-12. General recommendations for Digisonde 4D operations 3-60 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL # Recommendation 1 Use 7.5 or 5 minute meas- urement cadences for better coverage of storm time de- velopments in ionosphere Motivation 15 minute cadence is not sufficient to capture storm timeline Usage Implications Increased data volume 2 Use appropriate list of restricted frequencies Frequency allocation authority fines Decreased quality of data 3 Run tracker calibration schedule every 3 months Reflect long-term changes in the analog electronics None 4 Do not leave digisonde ob- Data visualization uses computer servatory with DCART show- resources ing real-time data on screen None 5 Do not leave digisonde ob- Data loss servatory with the sounder idling or running in the Manual/Diagnostic state. None SECTION 3 OPERATING INSTRUCTIONS 3-61 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE CHAPTER 4 ADVANCED INTERFACE OF DCART DIGISONDE 4D SYSTEM MANUAL SUMMARY OF ADVANCED FEATURES IN DCART 3:122. The following categories of DCART operations are considered to be available to advanced users:  Programming and analysis of Cross-Channel Equalizing (CCEQ) data,  Programming and analysis of Tracking Filter Calibration data,  Direct hardware commanding,  Global redefinition of data production options,  Commanding of DESC into Diagnostic and Standby state for manual uploads, and  Manual production of SSTs. 3:123. Use Options – General menu of DCART to switch it into Advanced interface mode, in which DCART windows shows additional controls and content tabs (see Figure 3-44). Cross-Channel Equalizing of the Receiver Channels 3:124. The CCEQ operation switches Digisonde 4D into internal loopback configuration, in which antenna switch is commanded to use loopback signal from Transmitter Card instead of receiving antennas (Figure 3-44). Figure 3-44: Advanced mode of DCART interface (showing CCEQ Program definition). 3-62 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 3:125. CCEQ data are acquired to derive complex correction coefficients to channels 2, 3, and 4 that would equalize their transfer function to match channel 1. The CCEQ data are stored in text form in .CEQ files and sent to Dispatcher for their post-management (assembly in daily files, delivery to remote destinations, etc.). A copy of the latest CEQ operation is stored in D:\DISPATCH\ folder as LATEST.CEQ to use it for equalization step of the Processing Chain (see Chapter 1 for further details of signal processing in Digisonde 4D). Sample content of the .CEQ files is given in Table 3-13. Table 3-13: Sample CCEQ data file DIGISONDE CHANNEL EQUALIZING DATA Version: 0 Time of measurement: 2006.08.15 (227) 20:53:59 FREQ A1/A2 Ph1-Ph2 A1/A3 Ph1-Ph3 A1/A4 Ph1-Ph4 500 .9886 -.31 .9664 -1.27 .9248 1.45 550 .9673 1.17 .9351 .08 .9043 2.82 600 .9706 1.48 .9378 .47 .8974 3.31 650 .9556 1.28 .9357 -.77 .8995 1.70 700 .9612 .38 .9520 -1.23 .9107 .80 750 .9494 .09 .9315 -.58 .8959 1.13 800 .9724 -.75 .9628 -1.57 .9336 -.95 850 .9599 -.68 .9427 -.42 .9199 -.70 900 .9506 -2.03 .9252 -1.66 .9026 -2.09 950 .9522 -2.54 .9283 -2.33 .9071 -3.18 1000 .9761 -2.81 .9542 -2.80 .9332 -3.91 1050 .9803 -1.28 .9612 -.78 .9360 -2.05 3:126. CCEQ data are shown in the “Channel Equalizing” tab of DCART main display area using the standard 4-channel panel display shown in Figure 3-30 and Figure 3-31. Calibration of Tracking Filters 3:127. Tuning of the voltage-sensitive varicaps in the tracking filters of Digisonde 4D requires a calibration algorithm that finds the optimal control voltages for a predefine set of operating frequencies (see Figure 3-45 and Table 3-14 ). Figure 3-45: Tracker Calibration program SECTION 3 OPERATING INSTRUCTIONS 3-63 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Table 3-14. Tracker Calibration Frequencies # Filter Band 0 Low-Pass 1 Band 1 2 Band 2 3 Band 3 4 Band 4 5 Band 5 6 High-Pass Frequency range, MHz Below 0.5 0.5 – 1.2 1.2 – 2.92 2.92 – 7.02 7.02 – 15.67 15.67 – 32 MHz Above 32 MHz Frequency Stepping none 5 kHz 10 kHz 25 kHz 50 kHz 100 kHz none 3:128. Tracking filter calibration results are stored in TRACKER.DAT file in binary format, and can be exported from the Tracker Calibration visualization tab into a plane text file. DATA PRODUCTION MODES 3:129. It is possible to instruct Digisonde 4D to temporarily disable production of outgoing data files while design of the optimal measurement programs and schedules is underway. Click “Save Product Files” toggle button to NONE to disable file generation (see Figure 3-44). 3:130. It is also possible to alter the way DCART saves raw data in local files for every measurement made by sounder. Click “Save Raw Files” toggle button (see Figure 3-44) to modify raw file generation:  Raw Data = NONE (no raw data are saved),  Raw Data = PER PROGRAM (raw data are saved for those programs that have the option enabled),  Raw Data = ALL (raw data are saved for every measurement made). 3-64 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE CHAPTER 5 HOMEPAGE AND DATA DISSEMINATION DIGISONDE 4D SYSTEM MANUAL INTRODUCTION 3:131. The sounder operates WWW server that allow remote computer platforms to connect for data visualization and monitoring of the system health status. Figure 4-17 shows the sounder’s web homepage with access to the available visualization features. Figure 3-46: Digisonde homepage 3:132. The sounder homepage provides several publicly accessible “latest data” displays that automatically refresh remote screens with new data. There are also several interactive browsing pages that allow access to the images in the short-term archive at the sounder that holds recently made data (up to one month or more). Additionally, a long-term archive of ionogram-derived (scaled) data is available that stores years of data in SAO format, with access to the source files and an interactive Java applet for their visualization as time series. SECTION 3 OPERATING INSTRUCTIONS 3-65 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 3:133. Standard reports of the system health status, as well as screen capture from the DCART and Dispatcher programs are available on the sounder homepage, but restricted to public access. 3:134. Dispatcher utility of the Digisonde 4D is responsible for all post-analysis of data product files generated by DCART, and delivery of the source and derived products over the Internet to remote servers using FTP or SFTP. None of Dispatcher operations involve user interaction, and data delivery options are changed by editing of the configuration files on DATA platform. 3:135. FTP or SFTP deliveries of data files to multiple destination servers are organized by buffering of the file copies that need to be delivered in the outgoing folders D:\Buffers\FTP#\, where # is the server number. When delivery of a file to the destination server is successful, the file is deleted from the buffer folder. 3:136. When more than one remote destination is configured for data delivery from Digisonde 4D, the RoundRobin scheme is used, in which at any time only one FTP/SFTP connection exists, and destinations are serviced sequentially, in a loop, until all files are delivered. The Round-Robin scheme facilitates rapid delivery to the server #1 at the top of the list instead of sharing the available network bandwidth among multiple sessions. Thus, the delivery algorithm prioritizes destinations so that important deliveries (e.g., real-time stream to a space weather center) are made first. In addition, with only one connection existing simultaneously, there is less risk of cluttering the communications link and raising the risk of timed-out incomplete sessions. At the same time, the Round-Robin scheme has larger overhead when a destination server is not reachable and outgoing files are accumulating. To avoid additional attempts of connecting to a server that has previously rejected connections, the Round-Robin scheme is modified to exclude servers from the loop if they failed to respond. The next attempt to contact such unreachable server will be made after the current round is finished will all deliveries completed for operational servers. 3:137. FTP/SFTP deliveries are initiated (a) as soon as current measurement is completed and data products are available, and (b) periodically in between measurements to attempt resending the files that previously could not be delivered. 3:138. Table 3-15T lists the configuration files and their relevant sections that are involved in FTP/SFTP deliveries. Table 3-15. Configuration files involved in FTP/SFTP data deliveries # File 1 DISPATCH.UD D Configuration item 080 Outgoing Folder 081 File Extensions for uncompressed delivery 082 File Extensions for compressed delivery 083 Accumulation option 084 Remote Folder 085 Minutes to Include Comments Folder for buffering outgoing files List of standard file extensions for delivery without compression List of standard file extensions for delivery of compressed files using COMPRESS.BAT 1 if outgoing file is deleted only if it has been delivered successfully Folder at the destination server to change to Deliver files made on the given minutes of the hour 3-66 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL # File 2 ACCOUNT.FTP Configuration item 086 Latest Reports 087 FTP Command Line 088 Custom Compression Batch File 089 Custom FTP Batch File 990 Delay Secure Data Line 1: IP username password Line 2: options, space delimited Comments Additionally send another copy of the file named “LATEST.XXX” where XXX is file extension Use provided text for FTP command instead of the built-in FTP script. Use provided batch file instead of the COMPRESS.BAT to compress the outgoing file Use provided batch file to deliver data. The batch file can have access to two dynamically generated script files with appropriate FTP and SFTP commands: ftpcmd.in (FTP) and sftpcmd.in (SFTP) 1 – delay delivery of data until they are released into public domain IP or domain name of the destination server, username, password (clear text) passive – enforce passive FTP session active – enforce active FTP session predelete – include delete command in the script to delete same name file at the destination before starting delivery SECTION 3 OPERATING INSTRUCTIONS 3-67 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL CHAPTER 6 REMOTE ACCESS INTRODUCTION 3:139. Accessing Digisonde 4D sounder from remote locations is certainly a convenient possibility to avoid physical presence at the Digisonde observatory to perform commanding, configuration, software updating, and certain system diagnostic and troubleshooting tasks. Use of the commercial remote access tools for Windows is one welcome possibility whose degree of success depends on the bandwidth and reliability of the communications line to the sounder, as well as computer security considerations. Use of the low-level file transfer mechanisms for remote access is certainly less convenient but still a powerful way to control the sounder from afar. REMOTE ACCESS USING REMOTE DESKTOP SOFTWARE 3:140. Microsoft Remote Desktop Connection is standard software included with versions of Windows XP sp2 and Vista. It provides remote client full control of the DATA platform screen. However, it requires a relatively high bandwidth connection to operate sensibly. It also locks the local terminal at the digisonde site so that local user cannot share the desktop with remote user. 3:141. It is recommended to be wary of using local devices and resources (printers) and adjust settings to make best use of available bandwidth. REMOTE ACCESS USING FTP/SFTP CONNECTION TO DIGISONDE 3:142. In order for the DATA platform to accept message files from remote commanding consoles over the Internet, there are two common software solutions:  For sensitive installations -- Vandyke VShell, a standard secure shell server that includes SFTP server. Vandyke VShell does not require a high speed connection to operate.  In other cases – standard Windows ftp server, part of Microsoft IIS package. NOTE It is important to upload message files with added .TMP extension and rename them to the intended filename when the upload is completed, so that DCART or Dispatcher do not operate on the file while it’s transfer is still in progress. Commanding DESC operations 3:143. Limited commanding of the CONTROL platform is available via uploading COMMAND.REM file containing one line of text with the following possible contents:  -- reboot CONTROL platform  -- send STOP command to DESC  -- send Switch to Diagnostic mode command  -- equivalent to 3-68 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL  -- send “Switch to Automatic mode” command Updates to PROGSCHD 3:144. Contents of the active PROGSCHD at the sounder can be updated by uploading the [edited] progschd file to the DCART incoming folder D:\DPSMAIN\DPS2AUX\ as DCD.REM. NOTE Development of new programs, schedules, and SST planning rules shall always start with downloading currently active PROGSCHD from the sounder site. Active PROGSCHD file resides in D:\Dispatch\Control\ folder as “progschd” file. Uploads of the edited progschd files shall not be done by overwriting the active PROGSCHD file in D:\Dispatch\Control\ folder. Instead, upload progschd to D:\Secure\Incoming\ and rename it to DCD.REM. Control of Dispatcher 3:145. Simple remote control of Dispatcher operations is provided by uploading remote request files (.REQ) to incoming folder D:\Secure\Incoming\. It is possible to:  Restart DATA platform by placing RESET.REQ file with single line containing digit 2,  Re-read Dispatcher configuration file DISPATCH.UDD by placing an empty NEW_SETTINGS.REQ file. Upload of campaign requests DCART supports standard remove campaign requests (RCR) files generated by the ADRES request sub- system of the DIDBase. RCR files have two or more lines of plain text as described in Table 3-16. Contents of Remote Campaign Request file Line # 1 2 3 Contents Version descriptor Format VNN, where NN is version number Campaign Start timestamp yyyy.mm.dd. hh:mm:ss, Campaign Stop timestamp yyyy.mm.dd. hh:mm:ss, Schedule Number I3 Same contents and format as Line #2 3:146. . Comments Folder for buffering outgoing files Three items, comma separated Additional lines may be used to specify more than one campaign request SECTION 3 OPERATING INSTRUCTIONS 3-69 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Table 3-16. Contents of Remote Campaign Request file Line # 1 2 3 Contents Version descriptor Format VNN, where NN is version number Campaign Start timestamp yyyy.mm.dd. hh:mm:ss, Campaign Stop timestamp yyyy.mm.dd. hh:mm:ss, Schedule Number I3 Same contents and format as Line #2 Comments Folder for buffering outgoing files Three items, comma separated Additional lines may be used to specify more than one campaign request 3:147. Remote campaign request (RCR) files must use the following naming convention: UUUUU_YYYYDDDHHMMSS.RCR where UUUUU is URSI code of the station and YYYYDDDHHMMSS is campaign start date and time. RCR files are placed in the remote-command-incoming folder of DCART, usually configured to be D:\DPSMAIN\DPS2AUX\. 3-70 Section 3 OPERATING INSTRUCTIONS DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL SECTION 4 HARDWARE DESCRIPTION ______________________________________________________________________________ SECTION CONTENTS Page SECTION 4 4-1 CHAPTER 1 HARDWARE OVERVIEW..................................................................................... 4-5 System Description .................................................................................................................................... 4-5 CHAPTER 2 PROPRIETARY CIRCUIT BOARDS .................................................................. 4-10 DIGITAL TRANSMITTER CARD ............................................................................................................. 4-10 Functional Description......................................................................................................................... 4-10 Transmitter and Receiver Synchronization ......................................................................................... 4-11 Transmitter Control.............................................................................................................................. 4-12 Transmitter Output Modes................................................................................................................... 4-13 Transmitter Card ................................................................................................................................. 4-13 Digital Receiver........................................................................................................................................ 4-13 Gain Control Prior to Digitization ......................................................................................................... 4-14 Digital Receivers with TI Graychip ...................................................................................................... 4-15 Digital Receiver Board......................................................................................................................... 4-15 Tracking Bandpass Filters ....................................................................................................................... 4-17 Preprocessor Card................................................................................................................................... 4-19 Functional Description......................................................................................................................... 4-19 Data Interface to Control Platform....................................................................................................... 4-20 Preprocessor Board ............................................................................................................................ 4-20 Built-in Test Card ..................................................................................................................................... 4-21 Antenna Switch ........................................................................................................................................ 4-23 Polarization Switch................................................................................................................................... 4-25 Power Distribution Card........................................................................................................................... 4-26 Battery Interface Box ............................................................................................................................... 4-27 SECTION 4 – HARDWARE DESCRIPTION 4-1 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL RF Power Amplifier Chassis .................................................................................................................... 4-29 RF Amplifier Card ................................................................................................................................ 4-29 Half-Octave Filter (HOF) Cards (2 per system):.................................................................................. 4-30 CHAPTER 3 COMMERCIAL HARDWARE.............................................................................. 4-32 Cards and Assemblies Supplied from other Manufacturers .................................................................... 4-32 GPS OPERATIONS................................................................................................................................. 4-32 CHAPTER 4 Troubleshooting GPS receiver: Support informationError! Bookmark not defined. 4-2 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL List of Figures Figure 4-1: Block diagram of Digisonde 4D 4-5 Figure 4-2: Main Chassis of the Digisonde 4D 4-6 Figure 4-3: Power Amplifier Chassis of the Digisonde 4D 4-6 Figure 4-4: Digisonde 4D Front View 4-7 Figure 4-5: Digital Transmitter Block Diagram 4-10 Figure 4-6: Phase-modulated 16-chip code sequence with the sinusoidal shape of the chips achieves narrower transmission bandwidth 4-11 Figure 4-7: Transmitter PCB 4-13 Figure 4-8: Digital Receiver block diagram. Only 1 of the Graychips is used for current Digisonde 4D operation 4-14 Figure 4-9: Block diagram of a single channel of the GC5016 chip. RINF is receive input formatter, RSEL is receive input channel selector, NCO denotes digital oscillator, CIC is cascade integrator comb filter, and PFIR is programmable finite impulse response filter. 4-15 Figure 4-10: Frequency response characteristics of the digital receiver. Two different spectral shapes are currently used for the PFIR filter: Hann window and Gauss window. 4-16 Figure 4-11: Digital receiver PCB. 4-17 Figure 4-12: Tracking bandpass filters suppress out-of-band interferers. 4-17 Figure 4-13: Tracking bandpass filter PCB. 4-18 Figure 4-14: Preprocessor card block diagram and operations. 4-20 Figure 4-15: Preprocessor PCB. 4-21 Figure 4-16: General diagram of BIT signal sampling. 4-22 Figure 4-17: BIT card 4-23 Figure 4-18: Antenna Switch Block Diagram 4-24 Figure 4-19: Polarization Switch Block Diagram 4-25 Figure 4-20: Power Distribution Card Block Diagram (System Power) 4-27 Figure 4-21: Power Distribution Card Block Diagram. Continue. (BIT Card Interface) 4-27 Figure 4-22: DC Power Distribution Block Diagram 4-29 Figure 4-23: RF AMP 4-30 Figure 4-24: HALF OCTAVE FILTER (HOF) 4-31 SECTION 4 – HARDWARE DESCRIPTION 4-3 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE List of Tables Table 4-1: Transmitter Specifications Table 4-2: Transmitter Commands Table 4-3: Receiver Commands Table 4-4: Tracker Commands Table 4-3: BIT Card Commands Table 4-3. Listing of Commercial Peripheral Literature (TBR) DIGISONDE 4D SYSTEM MANUAL 4-10 4-12 4-17 4-18 4-23 4-32 4-4 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL CHAPTER 1 HARDWARE OVERVIEW SYSTEM DESCRIPTION 401. The system configuration is shown in Figure 4-1, with the layout of the Main and Power Chassis major components shown in Figure 4-2 and Figure 4-3. Figure 4-4 and 4-5 show the front and the rear views of the sounder. Figure 4-1: Block diagram of Digisonde 4D SECTION 4 – HARDWARE DESCRIPTION 4-5 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 4-2: Main Chassis of the Digisonde 4D Figure 4-3: Power Amplifier Chassis of the Digisonde 4D 4-6 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 4-4: Digisonde 4D Front View Figure 4-5: Digisonde 4D Rear View SECTION 4 – HARDWARE DESCRIPTION 4-7 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 402. The major sub-assemblies of Digisonde 4D include: a. Oven controlled 61.44 MHz frequency source (the Master Oscillator). b. Card cage with analog and digital cards for signal generation and reception. i. Digital Transmitter/Timing card ii. Four Tracking Bandpass Filter cards iii. Digital Receiver card iv. Pre-Processor card v. Built In Test (BIT) card vi. Backplane c. Control and Data Platform Computers- embedded Pentium Core2 Duo single board computers with passive PISA backplanes. Computer sub-system components are: i. Intel Pentium Core2 Duo processor ii. (Up to) 2 GB DDR2 667 MHz RAM iii. Intel 945GM Graphic Controller iv. 2 x Intel 82573L Gigabit Ethernet Controllers v. 2 x Serial ATA Interfaces vi. 1 x ATA Controller vii. 1 RS232 port viii. 1 RS232/RS422 port ix. 4 USB 2.0 ports x. 1 Mini PCI Socket xi. Compact Flash Type II Socket xii. ISA and PCI Interface via backplane d. Modular chassis mountable power board to convert the 24 to 28 V DC primary power or battery power to the precise +15, –15, +12, +5, +3.3, and –5 volts needed by various components in the system. The RF power amplifier circuitry can utilize the 24 to 28 V DC directly. e. Two x 150 W solid state RF power amplifiers operating over a range of 1 MHz to 40 MHz. f. Electronically switchable right or left hand circularly polarized active receiving antennas, powered and controlled by the Antenna Switch. 403. The Digisonde 4D hardware has been designed not only to replace the analog RF circuitry with their digital counterparts, but also to rework configuration of the embedded computers and corresponding data interfaces. As new powerful embedded computers and fast interface solutions have become available, it is now feasible to capture the complete set of the raw data for processing in the computer by implementing data processing functions in software written in a high-level language such as Java, taking advantage of conven- 4-8 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL ient development environments, debugging tools, and visualization libraries. In particular, it became possible to write software for elimination of narrow band interferers within each inter-pulse period prior to the application of the pulse compression and integration algorithms that were adapted from the DPS-4. 404. All relevant computations in the Digisonde 4D are managed by two embedded computer platforms. The Control Platform provides low-level hardware control and data acquisition functions, and the Data Platform processes the raw sample data. Processing in the Data Platform is done independently of the timedeterministic processes involved in controlling the measurements, thus permitting cleaner structuring of the real-time operations and their implementation as separate, well defined tasks under management of the RTOS. SECTION 4 – HARDWARE DESCRIPTION 4-9 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL CHAPTER 2 PROPRIETARY CIRCUIT BOARDS DIGITAL TRANSMITTER CARD 405. The transmitter specifications are given in Table 4-1. Table 4-1: Transmitter Specifications Function Output frequency Output voltage in transmission mode Output voltage in inter-channel calibration mode Size Control interface Supply voltages Value 0.1 MHz to 30 MHz 0.5 Vp-p to 1.5 Vp-p 45 mVp-p or 1 Vp-p 4” ½ X 5” Parallel Port +/- 5, +/- 15, +3.3 V Note Programmable, 32-bit precision Programmable Programmable EPP mode, 3.3 V Functional Description 406. Figure 4-5 shows the functional block diagram of the Digital Transmitter. Like its predecessor the DPS-4, the DPS-4D uses two transmitter channels to form left- or right-hand polarized signals by driving two orthogonal antennas. The transmitter design features two digital up-converters AD9857 by Analog Devices that can be independently programmed to have + or -90 of inter-channel phase difference (or 0º if linear polarization is required). Figure 4-5: Digital Transmitter Block Diagram 4-10 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 407. Both upconverters produce RF phase-coded pulses at the selected operating frequency using 16-chip Golay complementary codes. Onboard flash memory stores 16-chip code 1 and 2 sequences, as well as two selectable chip waveforms. In addition to the conventional square-wave chip waveform used in the DPS-4, a new sinusoidal shape is provided (see Figure 4-6). Changing the chip waveform shape from square-wave to sinusoidal results in a narrower transmission bandwidth. Initial measurements show that at 40dB below the main signal the sinusoidal waveform chip is 4 times narrower than its square-wave equivalent. Cleaner transmission comes at the expense of reduced transmitter power associated with the sinusoidal chip form, which we were able to compensate by additional processing of the received signal. Figure 4-6: Phase-modulated 16-chip code sequence with the sinusoidal shape of the chips achieves narrower transmission bandwidth 408. The phase modulation data are stored as I (real) and Q (imaginary) samples that determine the amplitude and phase of the up-converter output. I and Q data are read from the flash memory using a 1920 KHz PDCLK strobe produced by one of the up-converters. The PDCLK strobe clocks a counter that consecutively pre-fetches the modulation data from the memory, so that they become available to the transmitter by the next PDCLK. Transmitter and Receiver Synchronization 409. In order to sustain phase coherence of the digital up-converters and down-converters whose built-in frequency synthesizers are independent of each other, we synchronize them by the same 61.44 MHz clock provided as the LVDS differential signal from the master oscillator located on the card cage backplane. We also provide a synchronous start signal, called the reference or R-pulse and make sure that all up- and downconverters lock their phases to the R-pulse with high precision and minimum latency. 410. The transmitter board hosts a Timing PROM that provides R-pulses every 5 ms, together with other synchronization signals, including the hardware interrupt to the Control Platform. The Timing PROM holds 1 sec of DPS-4D life time, synchronized to the external GPS 1-sec pulse. Both PROMs of the transmitter board are controlled by the same PDCLK strobe to avoid mismatches due to unequal component aging. When the up-converters detect the R-pulse, they immediately clear the phase to zero. Resetting of the phase in AD9857 requires temporary setting of the operating frequency to zero, which is accomplished by momentary switching of the internal on-chip profile to a special profile with zero frequency. SECTION 4 – HARDWARE DESCRIPTION 4-11 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 411. To get the correct system time the sounder uses external GPS receiver usually mounted on the roof of the building DPS is installed in. DPS-4D communicates with GPS through RS-422 port on the data computer board. The GPS is powered using +12V constant voltage from the data computer through a dedicated pin inside the same cable as the RS-422 port uses. There is a polyfuse inside the adapter between computer power and the GPS cable. 412. Exact synchronization occurs at the front pulse edge of the one pulse per second signal from GPS. GPS generates one pulse per second to synchronize all internal time-critical circuits. It is connected to transmitter card timing logic through the inverting buffer on the card. Cause of that the 1PPS output of GPS has to be configured as 0 V pulse and positive idle. There is a pull-up resistor on the transmitter card making positive idle voltage if GPS is disconnected from the system. That allows the system run without GPS. Transmitter Control 413. The DPS-4D implements a new approach to the task of embedding control functions in hardware by using a combination of microcontrollers and programmable logic devices (PLDs). Though reliable microcontroller-based systems require a substantial initial investment in time and effort to put together, they accept future modifications at a low overhead, which comes as a benefit to evolving projects. We are particularly interested in engineering of the multiple-channel transceiver systems where sequential commanding of each channel in the transmitter and receiver appears inefficient. Microcontrollers relieve the Control Platform from repetitive transfers of the frequency commands over the control bus. 414. Our choice of the “P-Bus” for the system control bus still stands after three decades of digisonde development. The parallel port protocol remains a simple, commonly available solution in computers that, in its enhanced EPP mode, admits bi-directional operation and reaches adequate transfer speeds of 2 Mbit/s. For the transmitter board, we use the PIC18LF6520 microcontroller by MicroChip with two PLDs ATF1504ASV by Atmel. It takes about 2 μs for the PIC18LF6520 to accept one byte over the P-Bus, well below the P-bus timeout of 10 μs. To ensure deterministic synchronism of bus operations, the microcontroller is clocked with a 15.36 MHz signal derived from the master 61.44 MHz clock. 415. The AD9857 up-converters use the serial command interface, thus assigning the first task to the micro-controller to translate the parallel bytes from the system control bus to a serial 8-bit sequence. Direct routing of the incoming control bytes to the transmitter is done in so-called “pass-through” mode of microcontroller operations. The commands are listed in Table 4-2. PBus address 0x20h 0x21h 0x22h 0x23h 0x24h 0x25h 0x29h 0x2Ah 0x2Bh 0x2Ch 0x2Eh Table 4-2: Transmitter Commands Function of MCU Parameter (control byte / bytes) Pass through mode (write) Upconverter number Pass through mode (write) Upconverter internal register address Pass through mode (read / Upconverter internal register data write) Four byte frequency mode 32-bit frequency resolution (four data byte sequence) Two byte frequency mode 16-bit frequency resolution (two data byte sequence) RESET Any byte value Watch Dog timer control 0x00h – WDT is off, 0x01h – WDT is on Power Amp HOF control F0-F2 – channel #, F3,F4 – antennas / dummy loads Timing function control 0x0Ch / 0x4Ch interlaced – WDT feeding, time correction Main oscillator tuning 0x00h to 0xFFh tuning byte Transmitter control (waveform) Pulse type, polarization 4-12 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Transmitter Output Modes 416. Phase-aware multiple-channel RF instrumentation requires an additional design effort to have crosschannel differences in transfer functions calibrated out. In addition to the standard mode of transmitter operation when the output from the up-converters is routed to the RF power amplifiers, a cross-channel equalizing (CEQ) mode is also available for the loopback operations. In the CEQ mode, a small calibration signal is routed to the antenna switch, instead of the RF power amplifiers, for direct input to the receivers. Transmission modes are selected using analog switches that ensure that signals are present on either two main outputs or CEQ output. Transmitter Card 417. Figure 4-7 shows the transmitter card in its four-channel version (presently only two channels are used in the DPS-4D with the currently available software). Figure 4-7: Transmitter PCB DIGITAL RECEIVER 418. The receiver design considers operation in noisy RF environments where strong interferers could saturate the receiver inputs rendering the receivers insensitive to smaller message signals. For ionospheric sounding, AM radio stations in the 0.55-1.65 MHz band and the 6-24 MHz HF communications bands can pose serious problems for ground-based receivers. At some locations we have measured interference levels SECTION 4 – HARDWARE DESCRIPTION 4-13 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL of >1 V signals at the receive antennas compared to <1 μV message signals. Digital receivers that directly digitize RF signals are especially prone to this problem since ADCs have a limited dynamic range. 419. The ADCs need to be protected from powerful out-of-band interference as well as from saturating inband signals. In the DPS-4D, a combination of gain controls in the wideband input amplifiers and the analog tracking bandpass filters limit the input voltages at the ADCs to the maximum allowed values. Gain Control Prior to Digitization 420. The tracking bandpass filters feed the RF signals to the ADCs via selectable-gain amplifiers (Figure 4-8) that are digitally controlled in eight steps of 6 dB from -12 to +30 dB. Additional gain adjustments of 9 dB in the antenna switch and 9 dB in the Tracking Bandpass Filter are available. Total dynamic range of the gain adjustments prior to digitization then reaches 42+18 = 60 dB. Including the 96 dB dynamic range of the 16-bit ADC, the receivers can accommodate input signals varying over a range of 156 dB. 421. Amplifications in the Antenna Switch and the Tracking Filters (Figure 4-1) are time-controlled to accommodate diurnal changes in HF spectrum occupancy and ionospheric absorption. The selectable-gain amplifiers (Figure 4-8) are controlled on a per-frequency basis using a combination of the local under/over voltage (UOV) sensor and external commanding from the Control Platform. The UOV sensor monitors the three most significant bits at the 60-Msps ADC output and determines one of the three possible states, S = saturation, L = under-voltage, or N = no change needed. The UOV state is cleared immediately after the trailing edge of transmitter pulse and reported to the Control Platform prior to the next pulse. The Control Platform software makes appropriate 6 dB gain corrections if the S or L state is observed. Effectively, the automatic gain control ensures that the ADC input peak voltage remains below 1 V, that is, 6 dB below its saturation level of 2 V. Figure 4-8: Digital Receiver block diagram. Only 1 of the Graychips is used for current operation 4-14 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 422. A table of automatic gain selections for each of the operating frequencies is stored at the Control Platform and continuously updated with each run of the gain evaluation programs that cover frequencies from 0.1 to 30 MHz with 600 50 kHz steps. This table holds the gain settings for each frequency that will be used in the next ionogram sounding. Digital Receivers with TI Graychip 423. The Digital Receiver is designed around the Texas Instrument Graychip GC5016 (Figure 4-8) which has four independent digital synthesizers and four 16-bit digital inputs. Figure 4-9 shows the functional block diagram for one channel of the GC5016 chip configured as a digital down-converter. Figure 4-9: Block diagram of a single channel of the GC5016 chip. RINF is receive input formatter, RSEL is receive input channel selector, NCO denotes digital oscillator, CIC is cascade integrator comb filter, and PFIR is programmable finite impulse response filter. 424. The input data on port A[15..0] are converted to a complex input format (I and Q samples) in the receive input formatter (RINF). In this common configuration, each down-conversion channel demodulates the sampled data down to the baseband, then performs a low-pass filter operation, reduces the signal rate (decimation), and outputs I and Q baseband data. The mixer stage provides the receive input channel selector (RSEL), digital oscillator (NCO), and complex mixing logic (mixer) to translate the input data down to the baseband. After the mixer, the 5-stage cascade integrator comb (CIC) is used for filtering and decimation. After the CIC complex filter, the programmable finite impulse response (PFIR) filter provides CIC correction, spectral shaping, and further decimation. 425. Currently there is the possibility of selecting between two programmed PFIR filter functions: Gauss window and Hann window. Figure 4-10 shows the measured frequency response characteristics of the digital receiver with two different PFIR settings. By default the Gaussian is loaded to the downconverters. The baseband data are delivered to the Preprocessor card. Further processing, including spread spectrum pulse compression and coherent spectral integration, are currently performed in the Data Platform. 426. A microcontroller (Figure 4-8) provides the bi-directional interface between the Control Platform and the receiver to arrange automatic gain control and appropriate frequency selection. The transmittergenerated B-Clock clears the receiver phases to zero in order to synchronize its operation with the transmitter. Digital Receiver Board 427. Figure 4-11 shows the front side of the Digital Receiver card. The four coaxial connectors on top of the card feed four input signals to the receiver circuits. The digital output signals are fed through the 96-pin DIN connector to the Preprocessor card. Each of the four inputs to the receiver card is transformer coupled to SECTION 4 – HARDWARE DESCRIPTION 4-15 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL a low-noise push-pull amplifier AD8008. The amplifier outputs are transformer coupled to the digitally controlled variable gain amplifier (CLC5526), followed by a symmetric driver (THS4503) of the 16-bit ADC (LTC2205) (Figure 4-8). The ADCs feed two GC 5016 Graychips (total of 8 receiving channels). Eight receiving channels are provided in this design for possible future expansion to twin frequency transmission. dB 90 85 Hann window 80 Gauss window 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 Frequency [kHz] Figure 4-10: Frequency response characteristics of the digital receiver. Two different spectral shapes are currently used for the PFIR filter: Hann window and Gauss window. 4-16 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL P_Bus address 0x40h 0x41h 0x42h 0x43h 0x4Ah 0x4Dh 0x4Eh Figure 4-11: Digital receiver PCB. Table 4-3: Receiver Commands Function of MCU Parameter (control byte / bytes) Pass through mode (write) Downconverter number Pass through mode (write) Downconverter internal register address Pass through mode (read / Downconverter internal register data write) Four byte frequency mode 32-bit frequency resolution (four data byte sequence) Antenna switch control Ant Switch and Tracker gain control and calibration switch Saturation sensor Read sensor register status / reset sensor register (run) Constant gain control 3-bit gain control of the Op Amps before digitizing TRACKING BANDPASS FILTERS 428. Analog bandpass filters at the receiver front end efficiently suppress the out-of-band interference since the filters are synchronously tracking the transmitter frequency. Figure 4-12 shows the block diagram of the Tracking Bandpass Filter. The input transformer splits the entire frequency range into five bands with switch points at 1.2, 2.9, 6.5, and 15.9 MHz, plus one low-pass filter for f < 0.5 MHz and one high-pass filter for f > 32 MHz (for future applications). The main filtering in each band is achieved with serial circuits in the input that are tuned with voltage-sensitive varicaps. For the high frequency band (f  16 MHz), an additional tuned parallel circuit at the output (top of Figure 4-12) further attenuates all signals with frequencies different from the tuning frequency. Figure 4-12: Tracking bandpass filters suppress out-of-band interferers. SECTION 4 – HARDWARE DESCRIPTION 4-17 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 429. The bandwidth of a serial filter is Δfs = Rs / 2π Ls, where Rs and Ls are the serial resistance and inductance of the tuned circuit, respectively. Using varicaps for the tuning keeps Ls constant, i.e., Δfs is constant in each band. The Ls values for each band were selected so as to make the relative bandwidth for each band ~10%. To make Δfs sufficiently small requires Rs to be small, which is accomplished by a step-down at the input and a step-up at the output of the serial filters. The bandwidth of a parallel resonance circuit, Δfp, is proportional to 1/Cp, and therefore increases with f 2 since 1/Cp = Lp (2πf)2. Figure 4-13 shows one of the four Tracking Bandpass Filter PCBs. Figure 4-13: Tracking bandpass filter PCB. P_Bus address 0x60h 0x61h 0x62h 0x63h 0x64h Table 4-4: Tracker Commands Function of PLD Parameter (control byte / bytes) Band control Sets the band for all trackers Channel 1 tuning voltage con- Sets the frequency tuning byte from tracker calibration trol file Channel 2 tuning voltage con- Sets the frequency tuning byte from tracker calibration trol file Channel 3 tuning voltage con- Sets the frequency tuning byte from tracker calibration trol file Channel 4 tuning voltage con- Sets the frequency tuning byte from tracker calibration 4-18 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 0x65h trol Saturation sensor file Read sensor register status / reset sensor register (run) PREPROCESSOR CARD 430. The Preprocessor card has been developed for the DPS-4D as a part of our strategic use of dedicated digital signal processing (DSP) hardware to build low-power, light-weight, space-qualified radio sounding instrumentation. Thanks to the use of DSP techniques, the UMLCAR-designed radio plasma imager (RPI) instrument on NASA’s IMAGE satellite was capable of detecting echoes coming from 50,000+ km distances at transmitted power below 1 W. With new DSP concepts in mind, the DPS-4D sounder has provisions for two preprocessor cards mated to the output of the digital receiver. Targeting space applications, we selected field-programmable gate arrays (FPGA) by Altera as the CPU of the preprocessor. 431. At this time the pre-processor performs all data formatting, routing, buffering, and output function selections, leaving plenty of space for future DSP algorithms like RFIM, which is currently performed on the Data Platform, and twin frequency operations. Functional Description 432. Figure 4-14 shows the block diagram of the Preprocessor card assuming twin frequency operation. The gray blocks represent functions that are implemented inside FPGA. Since the Graychips each output 16bit samples as a sequence of four 4-bit nibbles, the first Preprocessor operation assembles the nibbles into 16-bit words. Next, the two simultaneous receiver sample streams are interleaved with receiver 1 samples followed by receiver 2 samples. Then the interleaved samples are written to memory 1 sorted by receiver/antenna. At the end of the first sample record, the Preprocessor switches to copying mode and simply copies memory 1 into memory 2. After the copy, the Preprocessor switches back to sampling mode. During the next sampling interval, the second sample record is stored in memory 1 while the previous sample record is read from memory 2 to the control computer SECTION 4 – HARDWARE DESCRIPTION 4-19 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL freq 1 nibbles GrayChip 1 freq 1 control freq 2 nibbles GrayChip 2 freq 2 control Assemble Nibbles into Words freq 1 words freq 1 control Assemble Nibbles into Words freq 2 words freq 2 control Interleave Freq 0 and Freq 1 Preprocessor Operation: Sampling Write Rx Samples to Memory 1 freq 1 & 2 words Read Previous Samples from Memory 2 to IDE IDE Interface Samples to Control CPU Memory 1 Controller Memory 1 CY7C1325 256Kx18 Memory 2 CY7C1325 256Kx18 Memory 2 Controller freq 1 nibbles GrayChip 1 freq 1 control freq 2 nibbles GrayChip 2 freq 2 control Assemble Nibbles into Words freq 1 words freq 1 control Assemble Nibbles into Words freq 2 words freq 2 control Interleave Freq 0 and Freq 1 Preprocessor Operation: Copying freq 1 & 2 words Copy Samples from Memory 1 to Memory 2 IDE Interface Samples to Control CPU Memory 1 Controller Memory 1 CY7C1325 256Kx18 Memory 2 CY7C1325 256Kx18 Memory 2 Controller Figure 4-14: Preprocessor card block diagram and operations. 433. The purpose of the two memory chips is to provide double-buffering of the samples obtained from the Graychips. As the samples are stored in memory 1, they are sorted by antenna. Data Interface to Control Platform 434. A suitable PCI data acquisition board could be added to the Control Platform to arrange data delivery from the Preprocessor card. However, we found the ATA standard, i.e., the IDE interface for hard disk drives and CD-ROMs, to be adequate for the task of interfacing the Preprocessor to the Control Platform. The IDE controller in the Control Platform recognizes the Preprocessor card as a hard disk. Read operations are done by addressing an appropriate head (antenna) and sector (block of 128 ranges). 435. All necessary protocol support for direct memory access (DMA) to Control Platform memory has been provided in the Preprocessor’s FPGA. In this way, the load of the Control Platform is reduced and the data transfer speed significantly increased. In fact, preprocessor transfers are much faster in comparison with the several milliseconds typical for an actual hard disk drive. The DMA protocol is arranged appropriately, with the interrupts raised by the DMA controller of the preprocessor card once the DMA transfer is done. 436. In single frequency configuration DPS-4D may have simplified preprocessor card. In that case the card doesn’t contain the RAM memory, DACs and any analog parts, some connectors. The firmware for FPGA is simplified as well and doesn’t provide DMA mode. Because of twice less data stream for single frequency application the regular PIO mode is enough to handle the IDE traffic. The card may be updated to support twin frequency mode by addition of some missing parts and loading the appropriate firmware to the flash memory. Preprocessor Board 4-20 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 437. Figure 4-15 shows the Preprocessor PCB. Most of the logic on the Preprocessor card is implemented in the Altera Stratix EP1S25F780 FPGA. The EP1S25F780 FPGA has 500,000 equivalent gates, 2 M-bits of on-chip RAM, and 597 I/O pins. In addition to the FPGA, the card has two Cypress Semiconductor CY7C1325 256K x 18 synchronous SRAM memories. Data nibbles from the Graychips arrive via the 96-pin DIN connector. Properly formatted output samples are sent to the same connector that supports all signals of the standard IDE interface in ATA mode. Figure 4-15: Preprocessor PCB. 438. The 10-pin header in the upper right is used to configure the FPGA during development. The 10-pin header in the upper left is used to store the final FPGA configuration into flash memory for release. Two SMA connectors are diagnostic outputs that enable display of analog signals showing the output of the Graychips. BUILT-IN TEST CARD 439. The Built-in Test (BIT) operation is a diagnostic mode of the DPS-4D used to determine the system state of health. The BIT operation reads data from the sensors incorporated in the hardware as shown in Figure 4-16. Not all DPS-4D subsystems could be outfitted with BIT sensors (e.g., transmitting antennas do not have sensors). The Control Platform commands the BIT card to collect sensor signals in the multiple operating configurations of the DPS-4D so as to evaluate collected information for determinations regarding the status of both directly and indirectly sensed digisonde components. Further description of BIT function is provided in Section 6. SECTION 4 – HARDWARE DESCRIPTION 4-21 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 4-16: General diagram of BIT signal sampling. 4-22 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 4-17: BIT card P_Bus address 0x80h 0x81h 0x82h 0x83h 0x84h Table 4-5: BIT Card Commands Function of MCU Parameter (control byte / bytes) Power Amp power control 0x01h – PA is On; 0x00h – PA is Off Run (write) Any value initiates the test measurement procedure Tracker saturation sensor cap- Write – capture; Read – 2 bytes value ture Temperature sensor capture Write – capture; Read – 2 bytes value Digital sensors capture Power voltages, overtemp ANTENNA SWITCH 440. Four identical input stages (T1, 2, 3, 4 and U5, 6, 7, and 8) receive signals from each of four receive antennas. The block diagram is shown in Figure 4-18A. The input Jx1, Jx2 (x denoting the antenna number) comes via short wires from BNC connectors mounted on the side of the Antenna Switch’s RF shielded enclosure. These connectors are connected to lightning suppressers to isolate the chassis from current surges (induced by lightning or power faults) picked up on the 160 to 320 m RF coaxial cables coming in from the antenna field. Also, the DC voltage to power the receive antennas pre-amplifiers is applied to these cables: +16.5 V or +22.5 V switched voltage (O/X from J7.5) is applied to the center conductor (+16.5 V signals the pre-amplifier to use left-hand circular polarization while the 22.5 V indicates right-hand polarization). O/X enters from the Power Distribution Card through J1.5. T1, 2, 3 and 4 match the 50  signal from the coax- SECTION 4 – HARDWARE DESCRIPTION 4-23 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL ial cables to input impedances of U5, U6, U7, and U8. DX1 and DX2 limit saturation from the transmitter pulse to ±0.7V. J1.2, J1.10 and J1.12 bring in the antenna selection bits (A0, A1, and A2) written to the latch on the Transmitter Card. These lines represent the same functionality as the predecessor of DPS-4D. The new functionality is presented by signals HIGH, LOW, and G5 as addition to basic A0, A1, and A2. Figure 4-18: Antenna Switch Block Diagram 441. The control command decoder based on Atmel PLD ATF1504ASV may work either like a DPS-4 decoder or like a DPS-4D decoder. In the first case pin 12 of U13 must be grounded otherwise it must be connected to +3.3V power. The advantage of new decoding style (DPS-4D) is the possibility to shut down any separate antenna channel in case of the damage of that channel to avoid any noise interference to nondamaged channels. 442. The four inputs are fed through transformers T1-T4, then through op amps U1-U4 into analog switches U11, U21, U31, and U41. The second input to the switches is a calibration signal generated on the Transmitter Card. The choice of switching between the antenna inputs and calibration signal is software controlled by the CAL signal on the J1 plug to the switchbox. The calibration signal level is dependent on 4-24 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL the gain setting selected by the user in the DCART menu. The software configures switches U5 and U6 to attenuate the level to 75mV, 2.5mV, 650uV, or 160uV. The four outputs of the antenna switch, either antenna signals or calibration signals, are fed out of the switchbox on SMB connectors, into the top of the (four) Receiver Card(s). 443. Every amplifier U5, U6, U7, U8 has a programmable gain control for signals from antennas using switches U1, U2, U3, U4 accordingly. The decoder can set two gains with 8 dB difference. 444. The decoder is based on flash memory and can be reprogrammed on-board using the 10-pin JTAG connector J3. POLARIZATION SWITCH 445. With two channels, one for the North (N) – South (S) loop and another for the West (W) – East (E) loop, the Polarization Switch (Figure 4-19) allows the receiver to receive circularly polarized signals arriving from overhead (i.e., small zenith angles) and to change the desired sense of rotation of the polarization vector. +12VA N S 2: 8+8 AMP CLC 426 LEGEND VOLTAGE REGULATOR A To Hybrid A +12VB +12VA Q22 +12VB W E 2: 8+8 AMP CLC 426 17/24V +12VB Figure 4-19: Polarization Switch Block Diagram LG To Ant. Switch C To Hybrid C (in Southern Hemisphere) B To Hybrid B VIS5- SECTION 4 – HARDWARE DESCRIPTION 4-25 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 446. For that purpose a 90 phase shifter is attached to the two outputs of the low-noise amplifiers which are equal to within 1 dB in amplification for the whole frequency band used. Thus the two channels are almost equal in design although only the W–E channel is switched. 447. Polarization switching is accomplished by switching the DC power fed through the same cable that brings the RF signal to the Antenna Switch. Two voltage regulators make the voltage (12 VDC) applied to the amplifier independent of the supply power, which changes between 17 and 24 VDC. This change is sensed by a transistor, the base of which feeds this voltage to a Zener diode. 448. The transistor current or the current to ground make one of the two diodes conduct which connects one or the opposite output of the input transformer to the W–E amplifier. This 180 change in one of the two channels provides the polarization change of the turnstile loop antenna with the help of a 90° wideband hybrid adder. 449. For signals arriving from remote stations with larger than 45° zenith angles the suppression of unwanted polarization depends strongly on the orientation of the turnstile antennas. An optimum configuration would be for the loop planes to be 45° off the direction toward the remote sounder. POWER DISTRIBUTION CARD 450. Power distribution within the sounder chassis is centralized in the Power Distribution (PWR) Card (shown in Figures 4-20 and 4-21). Fusing (with self-resetting overload devices), voltage regulation and current limiting are applied as necessary. Along the top of the card are LED’s to indicate the presence of various voltages. Red LED’s indicate a positive voltage, green indicate negative voltages and amber indicate the 24 V – 28 V input power for all DC/DC converters. An auxiliary function of this card is to switch the voltage level of the power sent to the magnetic loop preamplifiers to switch received polarization sensitivity (lefthand and right-hand circular). The card also provides a mounting for the DC/DC converters and collects several BIT signals into connector P5 to output them to the BIT Card. Figure 4-22 shows the overall power distribution within the sounder system. 4-26 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 4-20: Power Distribution Card Block Diagram (System Power) Figure 4-21: Power Distribution Card Block Diagram. Continue. (BIT Card Interface) BATTERY INTERFACE BOX 451. The functions of the battery interface are to provide: a) current to the VIS chassis, the RF Amp, and the cooling fans b) overvoltage protection c) an undervoltage shutdown d) overcurrent protection e) a timer to re-attempt powerup if a shutdown occurs f) a meter to observe the batttery/+28V power supply voltage. 452. After an initial delay of 10 seconds by the 555 timer (U6), the two parallel P-channel power MOSFETS (Q4 and Q5) are turned on, and current is provided to the RF Amp, VIS chassis, and cooling fans through the terminal strip connections on top of the Battery Interface Box housing. 453. Overvoltage is monitored by the voltage divider R35, R39, and R30 and the comparator U3. If there is an overvoltage condition, the comparator changes state and the power FETs and LED shut off. 454. Undervoltage is similarly monitored by the divider formed by R31 and R34. If the voltage drops below the set threshold, shutdown occurs. 455. Overcurrent is sensed by the voltage drop across the drain and source of the power FETs Q4 and Q5 by the voltage divider consisting of R51, R52, R53, and R54 in conjunction with the divider used by the overvoltage circuit. SECTION 4 – HARDWARE DESCRIPTION 4-27 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 456. If any of the failure conditions shut the interface down, the 555 timer will re-attempt powerup. If the cause of shutdown is no longer present, it will power-up successfully. Shorting J8 and J9 is a means of externally disabling the timer interface. 4-28 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 4-22: DC Power Distribution Block Diagram RF POWER AMPLIFIER CHASSIS 457. The RF Amplifier consists of the aluminum chassis drawer, a power relay (24V solenoid) for switching the +26.5V input from the battery/power supply. The power relay is controlled by the front panel switch and by an FET on the RF Amp card which is commanded by input from the upper chassis via the RF Amp IO connector. The chassis also houses the dual channel RF Power Amplifier card, with two independent amplifiers both capable of 150-200W output, and the two Half-Octave Filter (HOF) cards. The chassis front panel green LED displays the presence of primary power to the cards, and the two amber LED’s indicate the presence of transmitted power being output to the antennas from each of the two independent amplifiers located on the RF Amplifier card. RF Amplifier Card 458. The RF Amplifier is comprised of two independent wideband amplifiers (referred to below as the two channels) consisting of three stages, two drivers and a final (see Figure 4-23). The input signal to each amplifier channel is 1.4Vp-p, falling off slightly at the higher frequencies. The input cable is terminated in a PI attenuator made up of a 68, 330, and 68 ohm resistors where the 220 ohm is bypassed by a 68p capacitor to boost up the high frequency output. Each input stage (comprised of a Motorola hybrid module) amplifies 10mW up to 0.5W. The output of the second stage is 20W (40Vp-p across 22 ohms at the input to the final) and the output of the final stage is 200W. The entire 10 inch x 6 inch board is mounted to a 10 inch by 6 inch heat sink. The input voltage is the system’s primary power of 25 to 28VDC, from the power supply and the batteries in parallel, via the battery interface box. This input voltage is protected through a 15A fuse (not shown on the block diagram) at the input of the 25 to 28V DC to the board. The primary power is applied at the output end of the amp board where it feeds power, via the center tap on the primary of the 1:6 wideband transformers, to the 300V output stages. It is also routed back off the board to a twisted pair which runs down the underside (the fin side) of the heatsink to feed power to the small signal end of the board. Keeping this twisted pair on the back side of the AMP heat sink reduces coupling between output RF and input power, thus reducing the danger of a positive feedback situation (i.e. oscillation). INPUTS P3 XMTR ON +24 VDC LEVEL ADJUST MOSFET Volt Reg P1 XMTR1 P2 XMTR2 BIAS VOLTAGE AMP AMP AMP MHW-592 AMP MRF-141G AMP AMP MRF-141G OUTPUTS Envelope Detector 14 11 BIT P2 XMTR1 P3 XMTR2 Envelope Detector 12 9 BIT SECTION 4 – HARDWARE DETSehneSrsmorCal RIPTION18 5 4-B2IT9 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 4-23: RF AMP 459. The critical setting in the RF AMP is the bias voltage set by R67/147 for the input stages and R107/187 for the output stages. The bias voltage is pulsed, rising when the R BNC signal (Xmtr On from the regulated front panel input from the upper chassis) rises. The R BNC, via U41 and Q52/53 also applies the regulated +18V to amplifiers A1 and A2. The turn-on voltage for various batches of MRF-141G MOSFET transistors varies widely, but the bias voltage needed to set an idle current of about 2A is usually in the range of 2-4V. When the negative swing of an input sine wave exceeds 1V below the bias level, the FET is in its non-linear cutoff range, thus causing harmonic distortion in the output signal. The input and feedback resistors linearize these amplifiers greatly since the gate voltage becomes a virtual ground (i.e. the signal should theoretically approach zero since the output is inverted compared to the input and is larger by the same ratio as the feedback resistance–to-input resistance). 460. The design of the wideband transformers is crucial. A transmission line transformer needs to be constructed with a transmission line which has an impedance which is the geometric mean of the input and output impedances. For instance, matching a MOSFET output impedance of 2 ohms (1.5 ohms augmented with the 0.5 ohm resistors) to a 50 ohm output impedance requires a 10 ohm transmission line. Half-Octave Filter (HOF) Cards (2 per system): 461. Since the harmonic content of the RF Amplifier is too high for most frequency allocation agencies to authorize, the final output is passed through one of eight low-pass filters, depending on output frequency. The switch points are controlled by software in the D:\Dispatcher\StationSpecific.udd file. The upper cutoff frequency in MHz for each band is given as: 1. 1.69 2. 2.45 3. 4.10 4. 5.55 5. 10.95 6. 16.15 7. 22.1 8. 42.0 462. The filter channel is selected by 3 digital bits F0-F2 from the upper chassis (originating in the XMT card, and fed through the 25-pin AMP IO connector) which activate reed relay switches which conduct the RF signal to the selected filter. Two more bits F3 & F4 command the two output switches (also RF reed relays), directing the power to one of two antennas. Nominally one antenna is oriented for vertical incidence (thus VIS) and the other is oriented for oblique incidence (thus OIS). In case of vertical only configuration, OIS output is connected to dummy load. Dummy load is a 50 Ohm resistor is used for built-in-test purposes. The LS138 logic ICs decode the F0-F2 bits and the high voltage (+18V is connected through the solenoid winding to the IC’s output pin) open-collector non-inverting buffer (7407) provides the drive to pull down the relays of the appropriate filter channel (see Figure 4-24). 463. Power off command comes from BIT card and controls a large relay to connect power amplifier to +24V lower chassis main power. If there is no BIT card at appropriate spot in upper chassis this relay is ON by default as lower chassis is powered. 4-30 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 4-24: HALF OCTAVE FILTER (HOF) SECTION 4 – HARDWARE DESCRIPTION 4-31 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE CHAPTER 3 COMMERCIAL HARDWARE DIGISONDE 4D SYSTEM MANUAL CARDS AND ASSEMBLIES SUPPLIED FROM OTHER MANUFACTURERS 464. There are cards and assemblies provided by external manufacturers that are integrated into the digisonde. For simplicity, reference is directed to the applicable literature provided with each of these cards and assemblies. Copies of these documents are shipped with unit. For additional copies please contact: University of Massachusetts Lowell Center for Atmospheric Research 600 Suffolk St. Lowell, MA 01854 Reinisch@cae.uml.edu or http://ulcar.uml.edu 465. A listing of card assemblies and applicable commercial documentation is provided in Table 4-6. Table 4-6. Listing of Commercial Peripheral Literature (TBR) Board/Assembly Description GPS Receiver Manufacturer Trimble Navigation Single Board Computer DVD Drive Hard Disk Commell HS-872P Industrial Computer Source Industrial Computer Source Document Title Smart Antenna Developer’s Guide, Acutis, Acutime, Acutime II User Guide CONFIGURING GPS FOR OPERATIONS WITH DIGISONDE 4D 466. There is a special utility loaded on the data computer to configure and control the GPS receiver D:\Miscellaneous\AcutimeGold\AcuGold_Mon.exe. To configure the receiver with different settings than default ones it must be launch manually. Before that the time service must be stopped. It can be done using utility D:\NTP\bin\ntpd.exe. The service itself is in C:\Program Files\meinberg\ntp_time_server_monitor\mbgtsmon.exe. The DPS-4D control software obtains a correct time from GPS using that service program running on the data computer. 467. GPS is pre-configured to work with DPS-4D. In case of troubleshooting or replacing of the receiver see GPS configuration instructions in Table 4-7. 4-32 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Table 4-7: Configuring GPS Receiver Configure GPS Settings  Desktop / Utilities / NTP Time Server Monitor  Click “Stop NTP Service”  Minimize NTP Time Server Monitor Utility  Desktop / Utilities / AcuGold_Mon Serial Port Selection: COM 2 Are you using Acutime Gold with NTP monitoring? Yes  Setup / Packet Masks and Options…  Synchronous 8F-0B on Port A: Unchecked  Event 8F-0B on Port A: Checked  Synchronous 8F-0B on Port B: Unchecked  Event 8F-0B on Port B: Checked  Synchronous 8F-AD on Port A: Checked  Event 8F-AD on Port A: Checked  Synchronous 8F-AD on Port B: Checked  Event 8F-AD on Port B: Checked  Auto TSIP Outputs: Checked  8F-20 on Port B: Checked  8F-AB on Port A, Port B: Unchecked  8F-AC on Port A, Port B: Unchecked  Output XYZ ECEF (Packet 83): Unchecked  Output LLA (Packet 84): Checked  LLA Output MSL geoid: Unchecked  LLA Input MSL geoid: Unchecked  Double-Precision: Checked  Output 8F-20: Unchecked  Output XYZ ECEF (Packet 43): Unchecked  Output ENU (Packet 56): Checked  Position fix time tags in UTC: Checked  Compute fix on integer second: Unchecked  Output fix on request only: Unchecked  Synchronize measurement: Unchecked  Minimize projections: Unchecked  Raw measurements (Packet 5A): Unchecked  Doppler smoothed codephase: Checked  Output signal level in dBc/Hz: Unchecked  (Click the appropriate “Set”s)  Setup / Timing Outputs…  Driver Switch: Enabled  Time Base: UTC  Polarity: Positive (but the 1PPS is negative going, because we are taking off the 1PPS minus [there are 2 1PPS out- puts provided for in the GPS])  PPS Offset: 0e+00 SECTION 4 – HARDWARE DESCRIPTION 4-33 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL  Bias Uncertainty Threshold:  Output Options:  PPS Width:  (Click the appropriate “Set”s)  Setup / Save Configuration Segments  NTP Time Server Monitor / Start NTP Service 300.00 Always 1.000e-05 OK and Exit Verify GPS and Cable  GPS can communicate with NTP service and set the computer time.  Instructions: Go to NTP Time Server Monitor / NTP Status and ensure the “Reach” parameter is not zero and the line is not grey. If it is then attempt to set the computer time using the GPS manually through the AcuGold utility (File).  Notes:  GPS 1PPS is present and negative going, 10us.  Notes: 4-34 SECTION 4 – HARDWARE DESCRIPTION DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL SECTION 5 SYSTEM SOFTWARE _______________________________________________________________________________ SECTION CONTENTS Page SECTION 5 5-1 CHAPTER 1 SYSTEM SOFTWARE OVERVIEW...................................................................... 5-8 GENERAL DESCRIPTION ........................................................................................................................ 5-8 CHOICE OF SOFTWARE VERSUS HARDWARE IMPLEMENTATIONS................................................ 5-8 CHAPTER 2 SYSTEM SOFTWARE OF CONTROL COMPUTER.......................................... 5-10 INTRODUCTION ..................................................................................................................................... 5-10 DESC Block Diagram .............................................................................................................................. 5-10 GPS SYNCHRONIZATION ..................................................................................................................... 5-12 CHAPTER 3 SYSTEM SOFTWARE OF DATA COMPUTER ................................................. 5-13 INTRODUCTION ..................................................................................................................................... 5-13 Block Diagram of Data Platform Software........................................................................................... 5-13 DCART..................................................................................................................................................... 5-14 DISPATCHER.......................................................................................................................................... 5-15 CHAPTER 4 POST-PROCESSING SOFTWARE.................................................................... 5-19 POST-PROCESSING at DATA PLATFORM............................................................................................ 5-19 ARTIST .................................................................................................................................................... 5-20 Autoscaling Confidence Level (ACL) of ARTIST-5 ............................................................................. 5-21 ARTIST-5 Ionogram Qualifiers ............................................................................................................ 5-21 Long-term Statistical Evaluation of Digisonde-4D Accuracy............................................................... 5-22 Sensitivity study of ionogram-derived data accuracy.......................................................................... 5-22 Error bars for autoscaled critical frequencies...................................................................................... 5-22 Error boundaries for EDP .................................................................................................................... 5-24 SECTION 5 SYSTEM SOFTWARE 5-1 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Processing Precise Ranging Data in ARTIST ..................................................................................... 5-25 DFT2SKY ................................................................................................................................................. 5-26 DDAV........................................................................................................................................................ 5-26 TILT .......................................................................................................................................................... 5-26 DRGMAKER ............................................................................................................................................ 5-26 ION2PNG ................................................................................................................................................. 5-27 SKY2PNG ................................................................................................................................................ 5-27 DRG2PNG ............................................................................................................................................... 5-27 DVL2PNG................................................................................................................................................. 5-27 ANNEX A A5-1 DESC TO DCART INTEFACE CONTROL DOCUMENT A5-1 COMMON DEFINITIONS.........................................................................................................................A5-1 Structured data ....................................................................................................................................A5-1 Field.................................................................................................................................................A5-1 Primitive field types .........................................................................................................................A5-1 COMMON PACKET FORMAT.................................................................................................................A5-2 COMMON DATA ELEMENTS .................................................................................................................A5-2 Measurement Program ........................................................................................................................A5-2 Empty Program ...............................................................................................................................A5-3 Sounding Program ..........................................................................................................................A5-3 Built-In Test Operation ....................................................................................................................A5-8 Cross-Channel EQ Operation .........................................................................................................A5-9 Tracker Calibration ........................................................................................................................A5-10 Time Stamp .......................................................................................................................................A5-11 Schedule ............................................................................................................................................A5-12 Housekeeping Header.......................................................................................................................A5-12 Restricted Frequency Interval List .....................................................................................................A5-13 SCIENCE DATA PACKETS...................................................................................................................A5-13 Science Data considerations .............................................................................................................A5-13 Science Data Packet structure, packet type 0x81.............................................................................A5-14 Major Release Version..................................................................................................................A5-15 Science Data Packet General Header ..........................................................................................A5-15 Packet Preface ..............................................................................................................................A5-15 Packet Group Header ...................................................................................................................A5-15 Databins ........................................................................................................................................A5-16 HOUSEKEEPING PACKETS.................................................................................................................A5-19 5-2 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL I’m alive packet TYPE=0x01, Length = 38. ....................................................................................... A5-19 Event Message packet TYPE=0x02, Length is variable but not less than 41 .................................. A5-19 Error message packet TYPE=0x03, Length is variable but not less than 41.................................... A5-19 PROGSCHD Countdown packet TYPE=0x04, Length = 45 bytes ................................................... A5-19 BIT packet TYPE=0x05, Payload length =179 bytes ........................................................................ A5-20 Trackers Calibration data packet TYPE=0x06, Payload length is variable .................................. A5-22 TELEMETRY PACKET SUMMARY ...................................................................................................... A5-22 ERROR/EVENT ID AND AUXILIARY INFORMATION ......................................................................... A5-22 ANNEX B A5-25 DCART TO DESC INTEFACE CONTROL DOCUMENT A5-25 COMMAND PACKETS .......................................................................................................................... A5-25 Periodic Message packet TYPE=0x70, Length = 17. ....................................................................... A5-25 Switch to Standby state packet TYPE=0x81, Length = 0. ................................................................A5-25 Switch to Diagnostic state packet TYPE=0x82, Length = 0.............................................................. A5-25 Switch to Scheduled Operations state packet TYPE=0x84, Length = 0........................................... A5-25 Load program packet TYPE=0x71, Length = LEN............................................................................ A5-25 Start program packet TYPE=0x72, Length = 1 ................................................................................. A5-25 Stop currently running program packet TYPE=0x73, Length = 0. .................................................... A5-26 Load schedule packet TYPE=0x74, Length is variable .................................................................... A5-26 Start schedule packet TYPE=0x75, Length = 1 ................................................................................ A5-26 Load Start Schedule Time (SST) packet TYPE=0x76, Length = 18 ................................................. A5-26 Flush Start Schedule Time (SST) Queue packet TYPE=0x32, Length = 0 ...................................... A5-26 Load Restricted Frequency Interval List packet TYPE=0x77, Length is variable ............................. A5-26 Clean Restricted Frequency Interval List packet TYPE=0x78, Length = 0....................................... A5-26 Reboot TYPE=0x79, Length = 0. ...................................................................................................... A5-27 Auto-drift Message packet TYPE=0x33, Length = 25....................................................................... A5-27 Global Parameters packet TYPE=0x85, Length = 3. ........................................................................ A5-27 Trackers Calibration Data packet TYPE=0x06, Payload length is variable ...................................... A5-28 Amplifier Half-Octave Filter Switch Frequencies Table TYPE=0x86, Payload length is variable..... A5-28 COMMAND LIST SUMMARY................................................................................................................ A5-29 ANNEX C A5-30 DCART INTEFACE CONTROL DOCUMENT FOR DATA PRODUCTS A5-30 RAW SCIENCE DATA MEASUREMENT FORMAT ............................................................................. A5-30 General considerations ..................................................................................................................... A5-30 LEGACY SCIENCE DATA FORMATS: RSF AND SBF IONOGRAMS ................................................ A5-39 RSF Format: File Specification.......................................................................................................... A5-41 SBF Format: File Specification.......................................................................................................... A5-42 SECTION 5 SYSTEM SOFTWARE 5-3 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL LEGACY SCIENCE DATA FORMATS: DFT .........................................................................................A5-44 LEGACY SCIENCE DATA FORMATS: SAO.........................................................................................A5-47 SCIENCE DATA FORMATS: SAO.XML 5.0..........................................................................................A5-47 5-4 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL List of Figures UUUFigure 5-1: Digital data processing architecture of the Digisonde-4D. 5-9 Figure 5-2: Block-diagram of DESC software. 5-11 Figure 5-3: Digisonde 4D computer configuration with CONTROL and DATA platforms 5-14 Figure 5-4: Block Diagram of DCART software 5-15 Figure 5-5: Data routing within AUX computer 5-16 Figure 5-6: Error histogram of autoscaled critical frequencies of F2 layer obtained for 20675 ionograms from DPS-4 ionosonde at Průhonice, Czech Republic. 95% of all autoscaled values lie within the -0.45 to +0.15 MHz interval from the true values provided by manual scalers. 5-23 Figure 5-7: Error histogram of autoscaled critical frequencies of F2 layer obtained for 16,712 ionograms from DPS-4 ionosonde at Průhonice taken during quiet ionospheric conditions and auto-qualified as high confidence. Lower bound for foF2 error bar specification has improved from -0.45 to -0.3 MHz in comparison to the all ionogram case shown in Figure 5-6. 5-24 Figure 5-8: Autoscaled ionogram from Roquetes, Spain, with inner and outer error boundaries for calculated EDP. The error boundaries are obtained by modifying the original profile coefficients so that the boundary fits the anchor points as indicated. Error bars for foE, foF1. and foF2 critical frequencies are specific to the quiet confident ionograms at Roquetes (95% probability level). 5-25 Figure 5-9: Precision Ranging processing in ARTIST-5. The original ARTIST trace is shown as the yellow line, and the trace updated with Precision Ranging (PR) data is shown as the white line. Calculated PR values for each echo bin are shown as white numbers within the bin. When PR values are consistent over abutting range bins for the same frequency, their value (shown as white stars) is used to replace the conventional range directly. 5-26 List of Tables Table 5-1: Physical locations of data archival and incoming folders on AUX computer Table 5-2: Digisonde data that can be lost in case of irrecoverable AUX hard disk failure Table 5-3: UMLCAR post-processing software applications running on DATA Platform Table 5-3: Station UDD File Table 5A-5-2: Characteristics of Field Table 5A-5-3: Primitive field types Table 5A-5-4: Common Packet Format Table 5A-5-5: Empty Program Specification (length 1 byte) Table 5A-5-6: Data Processing structure (length 2 bytes) Table 5A-5-7: Sounding Operation (variable length) Table 5A-5-8: Frequency for Flex List (length 2 bytes) Table 5A-5-9: Built-in Test Operation (length 4 bytes) 5-17 5-17 5-19 5-19 A5-1 A5-1 A5-2 A5-3 A5-4 A5-5 A5-8 A5-9 SECTION 5 SYSTEM SOFTWARE 5-5 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE Table 5A-5-10: Channel Equalizing Operation (29 bytes) Table 5A-5-11: Trackers Calibration Operation (29 bytes) Table 5A-5-12: Trackers Bands (variable length) Table 5A-5-13: Tracker Band (length 5 bytes) Table 5A-5-14: Time Stamp (length 17 bytes) Table 5A-5-15: Schedule (variable length) Table 5A-5-16: Schedule entry (length 5 bytes) Table 5A-5-17: Housekeeping Header (length = 39) Table 5A-5-18: Restricted Frequency Interval List (variable length) Table 5A-5-19: Restricted Frequency Interval (length 4 bytes) Table 5A-5-20: DESC Release Version, length 3 byte Table 5A-5-21: Science Data Packet General Header, length 15 Table 5A-5-22: Packet Preface Specification, length variable Table 5A-5-23: Packet Group Header, length 6 (12 for debugging) Table 5A-5-24: Raw Databin, length 4 Table 5A-5-25: Doppler Databin format, length 4 Table 5A-5-26: Ionogram Databin format 1, without PGH, length 17 Table 5A-5-27: Ionogram Databin format 2, with PGH, length 19 Table 5A-5-28: Ionogram Databin format 3, length 4 Table 5A-5-29: “I’m alive“ packet structure Table 5A-5-30: Event Message packet structure Table 5A-5-31: Error Message packet structure Table 5A-5-32: PROGSCHD Countdown packet structure Table 5A-5-33: Hardware Sensors payload structure Table 5A-5-34: Static sensor data collected in BIT Table 5A-5-35: Dynamic sensor data collected in BIT case 0, 1, 2, and 3 Table 5A-5-36. Digital Sensors Table 5A-5-37. Analog Static Sensors Table 5A-5-38. Analog Dynamic Sensors Table 5A-5-39: Tracker Calibration payload structure Table 5A-5-40: Error Message ID and Auxiliary Information Table 5A-5-41: Event Message ID and Auxiliary Information Table 5C-5-42: Measurement Header, length is variable Table 5C-5-43: Measurement General Header, length 7 bytes Table 5C-5-44: Measurement Preface Specification, length is variable Table 5C-5-45: Antennas configuration, length is variable, e.g. 58 (for 4 antennas) Table 5C-5-46: Coordinates configuration, length 12 Table 5C-5-47: Look Header, length 22 Table 5C-5-48: Frequency Header, length 22 Table 5C-5-49: Height-restricted Frequency Header, length 26 5-6 SECTION 5 SYSTEM SOFTWARE DIGISONDE 4D SYSTEM MANUAL A5-9 A5-10 A5-11 A5-11 A5-11 A5-12 A5-12 A5-12 A5-13 A5-13 A5-15 A5-15 A5-15 A5-15 A5-18 A5-18 A5-18 A5-18 A5-18 A5-19 A5-19 A5-19 A5-19 A5-20 A5-20 A5-20 A5-20 A5-21 A5-21 A5-22 A5-22 A5-24 A5-31 A5-32 A5-32 A5-33 A5-33 A5-34 A5-34 A5-35 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Table 5C-5-50: Look Group, length is variable but the same for all groups within the same measurement A5-35 Table 5C-5-51: Doppler Frequency Group, length is variable but the same for all groups within the same measurement A5- 35 Table 5C-5-52: Ionogram Frequency Group, length is variable but the same for all groups within the same measurement A5- 35 Table 5C-5-53: Raw Databin uncompressed format (format 0), length 4 A5-35 Table 5C-5-54: Raw Databin compressed format (format 1), length 2 A5-35 Table 5C-5-55: Doppler Databin uncompressed format (format 0), length 4 A5-36 Table 5C-5-56: Doppler Databin compressed format (format 1), length 2 A5-36 Table 5C-5-57: Ionogram Databin uncompressed format (format 0), A5-36 Table 5C-5-58: Ionogram Databin uncompressed format (format 0), A5-36 Table 5C-5-59: Ionogram Databin compressed format (format 1), without PGH, length 9 A5-36 Table 5C-5-60: Ionogram Databin compressed format (format 1), with PGH, length 10 A5-36 Table 5C-5-61: Ionogram Databin, antennas-convolved uncompressed format (format 2) without PGH, length 7 A5-37 Table 5C-5-62: Ionogram Databin, antennas-convolved uncompressed format (format 2) with PGH, length 9 A5-37 Table 5C-5-63: Ionogram Databin, antennas-convolved compressed format (format 3) without PGH, length 4 A5-37 Table 5C-5-64: Ionogram Databin, antennas-convolved compressed format (format 3) with PGH, length 5 A5-37 Table 5C-5-65: Ionogram Databin, very compressed format (format 4) without PGH, length 2 A5-37 Table 5C-5-66: Ionogram Databin, very compressed format (format 4) with PGH, length 2 A5-38 Table 5C-5-67: General Purpose PREFACE Specification 5-39 Table 5C-5-68: The RSF Header A5-41 Table 5C-5-69: Length of the RSF Frequency Groups Depending on Ionogram Settings A5-41 Table 5C-5-70: Content of an Individual Range Bin in RSF File Format A5-41 Table 5C-5-71: Individual Bit Sections of the Range Bin A5-42 Table 5C-5-72: RSF PRELUDE Byte Organization A5-42 Table 5C-5-73: The SBF Header A5-42 Table 5C-5-74: Length of the SBF Frequency Groups Depending on Ionogram Settings A5-43 Table 5C-5-75: Content of an Individual Range Bin in SBF File Format A5-43 Table 5C-5-76: Individual Bit Sections of the Range Bin A5-43 Table 5C-5-77: SBF PRELUDE Organization A5-43 Table 5C-5-78: DFT File Structure A5-44 Table 5C-5-79: Drift Header Information Stored Serially in LSB of Amplitudes A5-45 Table 5C-5-80: Drift Data Specification A5-45 SECTION 5 SYSTEM SOFTWARE 5-7 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE CHAPTER 1 SYSTEM SOFTWARE OVERVIEW DIGISONDE 4D SYSTEM MANUAL GENERAL DESCRIPTION 501. The purpose of the system software is to automatically operate the ionospheric sounder transceiver system to produce displays and product data files of real-time measurements, to report acquired data to remote data subscribers, provide public access to the local repositories of data, and to allow remote commanding and maintenance of the sounder. 502. The sounder contains two embedded computing platforms, CONTROL and DATA, running in parallel. Both computers load the software automatically on power-up and operate in the multitasking environment executing tasks of different priorities simultaneously. CONTROL platform operations are described in Chapter 2 of this Section. Chapter 3 details system software of the DATA platform. CHOICE OF SOFTWARE VERSUS HARDWARE IMPLEMENTATIONS 503. Current choice of the Digisonde 4D digital signal processing (DSP) architecture balances both specialized and generic computing platforms. Development of specialized DSP hardware continues to be part of UMLCAR strategy to build low-power, light-weight, space-qualified radio sounding instrumentation. At the same time, for the ground-based applications that do not require radiation hardening, inexpensive small-format embedded computers present a feasible alternative to the custom DSP hardware. Digisonde 4D system software reflects the existing balance between software and hardware DSP solutions and includes algorithms that are scheduled for eventual hardware implementation in the pre-processor card(s). 504. Figure 5-1 shows the Digisonde 4D block diagram identifying the data processing elements. With new DSP concepts in mind, the sounder provides two preprocessor cards mated to the output of the digital receiver. Targeting space applications, we selected field-programmable gate arrays (FPGA) as the CPU of the preprocessors, whose design admits implementation in various FPGA families, including generic Altera chips suitable for the Digisonde-4D, and radiation-hardened Actel versions that can operate in the harsh radiation environments. At this time the Digisonde-4D sounders are equipped with one preprocessor card that performs all data formatting, routing, double buffering, and output function selections, leaving plenty of space for future DSP algorithms like the RF interference mitigation (RFIM), which is currently performed on the Data Platform, and the twin-frequency operation (shown with dashed lines in Figure 5-1). 505. The Control Platform is an embedded computer that manages hard real-time tasks under control of the RTEMS operating system. The digital receivers are designed to appear to the Control Platform as an IDE hard disk drive whose contents can be read using a standard HDD driver. The Data Platform is another embedded PC that performs processing of the acquired sample data to create data products. The Data Platform runs a suite of processing algorithms ranging from pulse compression to ARTIST ionogram autoscaling and EDP calculation, and the derivation of ionospheric tilt angles from Doppler skymaps. 506. Software components in the signal processing pipeline are designed to accommodate real-time data stream of varying bandwidth, depending on the selection of measurement program parameters. All internal communications are protected with the packet queues that dynamically buffer data to wait for the destination component to become available. Online data visualization engine in DCART uses the mailbox mechanism to adaptively decimate data that are displayed in real-time. 5-8 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 5-1: Digital data processing architecture of the Digisonde-4D. SECTION 5 SYSTEM SOFTWARE 5-9 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL CHAPTER 2 SYSTEM SOFTWARE OF CONTROL COMPUTER INTRODUCTION 507. The Control Platform of Digisonde 4D sounder is responsible for:  Measurement progression control in accordance with the program specification  Hardware control  Setting up transmission and reception in all measurement modes  Initiation of hardware tasks  Data Acquisition  Collection of raw data during the measurements  Collection of housekeeping data during BIT  Packaging and delivery of the sample data to the Data Platform,  Scheduling digisonde measurements  Schedule progression control in accordance with the schedule specification  Switching schedules at given times  Synchronization to the GPS time reference  Accepting configuration changes:  Program and schedule definitions,  Schedule start times,  Restricted Frequency Interval Lists (RFIL),  Digital receiver configuration,  Tracking filter configurations.  Switching operational states in response to commands 508. The Control Platform operating software, Digisonde Embedded System Control (DESC), runs under the management of a Real-Time Operating System (RTOS) “RTEMS” that ensures time-deterministic execution of the software tasks. DESC BLOCK DIAGRAM 509. Block diagram of DESC is shown in Figure 5-2. Red lines in the DESC diagram denote “hard” realtime events driven by the 1 PPS heartbeat signal from the GPS receiver, 5 ms interrupts produced by the Timing PROM, and Data interrupt from Preprocessor card. These events are related to hardware control and acquisition operations that are precisely timed in the hardware by the Reference pulse (R pulse). The 5 ms interrupt 5-10 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL occurs prior to the R pulse for software to setup hardware registers and arrange for transfer of available data from Preprocessor card. Figure 5-2: Block-diagram of DESC software. 510. Individual tasks managed by the RTOS are enumerated in Figure 5-2 to indicate their priority levels used by the RTOS scheduler to allocate computer resources to the tasks that are ready to run. 511. Green boxes in Figure 5-2 correspond to the software tasks that are responsible for progression of the measurements in accordance with the PROGSCHD specifications of programs and schedules, and schedule start time (SST) queue. In order to start specified measurement schedules at specified start times, SST Task monitors the clock time to detect approaching match of the system clock time with the top SST in the queue. When the match is imminent, SST Task forwards the required schedule number to the Schedule Task for initiation. The Schedule Task follows the schedule specifications to start Program Task at appropriate times relative to the actual start time of the schedule. The Program Task is responsible for conducting measurement programs from the start to finish. It no longer uses the system clock for timing of events; instead, it counts 5 ms interrupts to progress the measurement (setup transmitter and receiver for each measurement look, enable transmission and reception). The Data task is responsible for acquiring 256 range samples that become available in the FIFO buffer of the Pre-processor card and forming data packets for delivery to DATA platform. The Data task is invoked by the interrupt handler that in turn is triggered by the Data interrupt from the IDE controller on preprocessor card. 512. Parser and Framer tasks (shown as yellow boxes in Figure 5-2) are responsible for communications with the DATA Platform. The Parser Task accepts incoming command packets to assure their proper format and SECTION 5 SYSTEM SOFTWARE 5-11 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL forwards them for execution to the Command Dispatcher. The Framer Task accepts outgoing telemetry data to format them appropriately for delivery to the DATA Platform. GPS SYNCHRONIZATION 513. All Digisonde 4D operations are kept synchronous with the GPS Universal Time (UT). The DATA platform runs standard Simple Network Time Protocol (SNTP) that accepts SNTP messages from the GPS receiver over the RS-422 port to keep Windows XP clock matched to UT. Synchronization of the digisonde circuitry is done in hardware: each Second-In-The-life (SITL) written in the Timing PROM is triggered by the heartbeat 1 PPS signal from the GPS receiver. As for the CONTROL platform, its synchronization involves combination of both software and hardware solutions. The same Timing PROM that is triggered to produce timing signals for one SITL of the sounder also generates 5 ms external tick interrupt that drives the computer clock of CONTROL platform. Thus, no drift of the CONTROL platform clock shall be expected unless 5 ms interrupt becomes unstable. To verify healthy synchronization of the CONTROL platform, and also to initialize its system clock after powering up, DESC software periodically analyzes UT stamp1 from the Periodic Messages generated by DCART. When the 5 ms interrupt handler of DESC identifies the “golden” interrupt (out of 200 per second) that coincides with the external 1 PPS heartbeat signal from GPS, DESC:  Checks if no measurement is ongoing and verifies that the latest periodic message from DCART is less than 1 sec old, in which case:  Compares its system clock with the (UT stamp from DCART periodic message + 1 sec), and if a mismatch is observed: o Ignores 3 cases of the time difference exactly ±1 sec, in which case accidental latency problem in the handling of the periodic messages is suspected. o Otherwise, changes the CONTROL platform clock time and generates software event message TYPE=0x02 with EventID=0009h (System clock changed) into outgoing telemetry stream. NOTE During normal operations of the sounder, no software messages “System clock changed” have to be observed in DCART log window, except for the first message when CONTROL platform clock is initialized. 514. Additional testing of CONTROL platform synchronization is done by DESC packet parser that monitors latency of DCART periodic messages and reports continuous resets of the CONTROL platform system clock, or mismatches greater than 1 sec, as software error message TYPE=0x03 with ErrorID=0011h (Unstable clock, cannot set time). 1 DCART Periodic Messages are generated on the round second, typically once a minute, with UT stamp given at 1 sec resolution. 5-12 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL CHAPTER 3 SYSTEM SOFTWARE OF DATA COMPUTER INTRODUCTION 515. The Data Platform is responsible for:  Accepting raw sample data collected by the Control Platform for o processing, o visualization, o packaging in standard files, o local backup to mass storage media, and o delivery to external data recipients.  Provision of the user interface for manual and unattended operations of the DPS-4D o Design of measurement programs, schedules, schedule switch rules, campaign requests o Commanding DPS-4D operations  Publishing of the acquired science and housekeeping data to the WWW Block Diagram of Data Platform Software 516. Block diagram of Data Platform operating software is shown in Figure 5-3. Digisonde Commanding and Acquisition Remote Terminal (DCART) is responsible for interfacing DESC operating software on the Control Platform to send commands and collect telemetry data, as well as reduction of the acquired raw data to ionograms and drift records and provision of user interface for manual and unattended operations of the DPS4D. Dispatcher arranges processing of the ionogram and drift records to obtain derived data products, manages storage and dissemination of all recorded information, and produces graphic representation of acquired data for publishing to the WWW. There is a collection of WWW support tools that service remote user requests for data displays and files. 517. SECTION 5 SYSTEM SOFTWARE 5-13 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 5-3: Digisonde 4D computer configuration with CONTROL and DATA platforms 518. DCART 519. Main functions of DCART software are:  Support of Science Operations o Program design o Schedule design o Daily operations design (scheduling rules) o Campaign events design  Real-time Data Processing and Visualization o Science data o Housekeeping data  Manual Commanding o Start and stop o Switching operating states 520. Figure 5-4 shows the block diagram of DCART software. DCART handles two distinct data streams, telemetry (incoming data from CONTROL Platform) and commanding (outgoing data to Control Platform). Correspondingly, the telemetry part of interface has the Parser thread responsible for syntactic analysis of incoming packets from the Network Driver, extracting their payload section, and referring it to the queue of the Payload Dispatcher. The commanding part of interface has the Framer thread responsible for proper packaging of the command payloads from its queue and delivering them to Control Platform via the Network Driver. 5-14 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 5-4: Block Diagram of DCART software 521. The Interface Control Document (ICD) for Command and Telemetry (C&T) traffic between DCART and DESC software components of Digisonde-4D is detailed in Annex A. Further details on the DCART science data processing and examples of the real-time displays can be found in the Section 3, Chapter 2 of the Manual. DISPATCHER 522. Dispatcher component of the DATA Platform is responsible for arranging generation of derived data products (scaled characteristics, directograms, skymaps, drift velocities, ionospheric tilts, MUF tables), WWW publishing and data dissemination to remote servers, and all associated file management. Dispatcher routes incoming files from DCART to appropriate post-processing software components, collects their data products, spawns picture-making tools for the WWW pages, prepares daily data files, manages secure and public sectors of local storage, arranges data delivery over the Internet by calling FTP and SFTP clients, sends appropriate control data to DCART, buffers data for permanent archival on removable media (CD or DVD). shows a block diagram of data routes within the DATA Platform. 523. The DATA Platform maintains three types of local data archives, (1) short-term archive holding selected raw and derived data for 7-10 days (or more); (2) long-term archive storing daily files for a prolonged period of time (years), and (3) permanent archive on removable CD or DVD media that required periodic replacement of the filled media. SECTION 5 SYSTEM SOFTWARE 5-15 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 5-5: Data routing within AUX computer 524. Newly made sounder data files appear in the Digisonde incoming folder from DCART. Dispatcher initiates processing of each new file and collects all associated source and derived data products in the Real-time data folder. As soon as processing is complete, new data records are appended to corresponding one-day files in One-day files folder, outgoing files for remote servers are placed in the appropriate FTP out folders, and image making programs are called to produce pictures for WWW publishing and place resulting image files in Latest pictures folder. 525. As soon as the hold-off time for restricted access to the latest data expires, individual files in Real-time data and Latest pictures folders are moved for public access to the Short-term data and Short-term pictures folders. It is possible to configure expiration time to be 0, so that data are released to public folders immediately. 526. At the end of the day, Dispatcher finalizes one-day files residing in One-day files folder. It is possible to archive selected one-day files on removable media (CDs or DVDs) and keep them on the hard disk in the public long-term archive. Depending on configuration of Dispatcher, one-day files are copied to CD Buffer folder for archiving to removable media, or to Long-term folder for storage on the hard disk. Considering limited local hard disk space at the DATA Platform computer, it is recommended to store only one-day SAO files with ionogram-derived data in the long-term archive. The SAO files in the long-term archive are accessed remotely over the WWW interface for visualization and download. 527. Dispatcher is configured to keep system log files and copies of ionograms that caused ARTIST software problems in Diagnostics folder. 528. Dispatcher keeps files in FTP-out and CD Buffer folders if the recipient is not ready to accept the data. This creates potential for unlimited accumulation of the files in these folders if the recipient does not come online for a long time (e.g., remote data server is inaccessible over the network, or filled media disk is not replaced with a blank media). Together with the Diagnostics folder that holds ionograms causing ARTIST problems, and Long-term folder holding one-day files indefinitely, these folders may cause disk overfill condition on the AUX computer. The disk overfill condition is indicated in the homepage of digisonde (see below). 5-16 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 529. Table 5-1 lists physical locations of the appropriate directories on the hard disk. Table 5-1: Physical locations of data archival and incoming folders on AUX computer NAME LOCATION FUNCTION Digisonde D:\DPSMAIN\DPS2AUX Incoming files from digisonde Remote commands D:\Secure\Incoming Incoming commands from remote platforms Real-time data D:\Secure\IndividualFiles All real-time individual files produced by the sounder One-day files D:\Decure\OneDayFiles One-day files in progress (for the current day) Latest Pictures D:\WWW\IonoGIF.secure D:\WWW\DrgGIF.secure Images produced within the period of restricted access to data D:\WWW\SkyGIF.secure D:\WWW\VelGIF.secure FTP out D:\Buffers\FTP1 Outgoing buffers for FTP-delivered data D:\Buffers\FTP2, etc. Short-term data D:\Secure\Public\ShortTerm Short-term archive of data files Short-term pictures D:\WWW\IonoGIF Image for public access D:\WWW\DrgGIF D:\WWW\SkyGIF D:\WWW\VelGIF CD Buffer D:\Buffers\RMD_1DayFiles Outgoing buffer for removable media (CD, DVD) Long-term D:\Secure\Public\LongTerm Long-term archive of one-day files Diagnostics D:\Secure\Diagnostics Diagnostic data 530. The preferred mode of sounder operations is “online delivery”, with newly acquired data immediately delivered to a remote central data repository over the FTP or SFTP connection. In this mode, no data management expertise is required locally at the sounder observatory, and all data operations are conducted at the central site where efficient management of multiple digisonde locations is possible. When the S/FTP deliveries are technically impossible or not feasible, local permanent archival on CDs or DVDs has to be maintained. 531. Continuous FTP deliveries and daily data backups to CD or DVD media shall minimize irrecoverable data loss in case of a complete loss of hard disk contents. Table 5-2 lists the locations of long-term and buffered data files that may be lost in the unlikely event of such permanent hard disk failure. Table 5-2: Digisonde data that can be lost in case of irrecoverable AUX hard disk failure LOCATION CONTENTS STORAGE PERIOD RECOVERY D:\Buffers\FTPx\ Outgoing files for delivery to remote data servers Nominally not more than a few minutes, unless remote server is inaccessible and data are buffered until server comes back online. Latest data are impossible to recover. Buffered data for inaccessible servers may be found on other online servers D:\Buffers\RMD* Files buffered for backup to CD or DVD Nominally not more than one day, unless CD is full and data are buffered until new CD is available Recoverable If data are delivered to remote servers. For sounders without remote delivery, all data are lost. D:\Secure\Public Long-term archive of one- many years \Longterm day SAO files Recoverable from offsite locations or backup media NOTE DATA Platform stores no irreplaceable software, and data loss in case of the hard disk failure are minimal (see Table 5-2). it is recommended that a copy of the hard disk contents is kept available at the sounder site to restore the disk in case of the hardware failure or Internet security breach. SECTION 5 SYSTEM SOFTWARE 5-17 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 532. Dispatcher is the infinite loop application whose continuous operations are critical for the remote unmanned ionospheric observatories. In order to ensure high reliability of the DATA Platform, Dispatcher continuously signals its state of health to the software and hardware watchdogs. The software watchdog is a Windows service that monitors history of Dispatcher signals and initiates system reboot if there is a gap of more than 10 minutes. It appears that the software watchdog reboot still leaves a number of conditions uncovered, in particular those involving Windows system critical stops. A hardware watchdog has been added to the system to ensure continuous operations through the events causing operating system faults. Its delay is set to be 15 minutes, so that the software watchdog would be able to attempt system reboot prior to the hardware power reset. 533. In addition to Dispatcher, another process permanently runs on DATA Platform, GUARDIAN, that has only one task of looking for remote system reboot command (which is a text file guardian.req placed in incoming command folder, D:\Secure\Incoming\). 534. All file copy operations within DATA Platfrom, including data deliveries over FTP, are made by first copying the file under a different file extension (TMP) and then renaming it to the original file extension. In this way, other software components do not attempt operations on files whose transfer is still ongoing. 535. Custom FTP client is used by Dispatcher to allow closer monitoring of the data delivery process. All server replies are captured in order to identify network delays and error conditions. The file is declared successfully delivered only after receiving acknowledgement of the rename operation for the destination file and confirmation that its size on the remote platform is not zero. Three timeouts are enforced on any particular FTP transfer, (1) maximum delay of any single packet transfer, (2) average packet delay of the sequential transfers, and (3) master timeout of the FTP delivery session. The FTP data deliveries to multiple destinations are serviced in the priority order specified in the DISPATCH.UDD settings file. The round-robin scheme is used to send a limited number of files at a time to multiple subscribed servers, so that delivery of the buffered files (files waiting for the remote server to resume online operations) would not affect prompt deliveries to other subscribers. 536. It is possible to configure Dispatcher for periodic modem connections for FTP deliveries (e.g., once an hour) instead of immediate connections as soon as data are produced to save on per-connection charges. 5-18 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE CHAPTER 3 POST-PROCESSING SOFTWARE DIGISONDE 4D SYSTEM MANUAL POST-PROCESSING AT DATA PLATFORM 537. The DATA Platform the Digisonde-4D sounder comes with pre-installed suite of UMLCAR software responsible for generation of derived data products. The list of installed post-processing UMLCAR software applications is given in Table 5-3. Annex B details data format for all source and derived data products of Digisonde-4D. Table 5-3: UMLCAR post-processing software applications running on DATA Platform NAME LOCATION CONFIGURATION FILE FUNCTION ARTIST D:\DISPATCH ARTIST.ini, xxx.UDD, xxx.RSL Ionogram Autoscaling DFT2SKY D:\DISPATCH DFT2SKY.ini, xxx.UDD Skymap calculation DDAV D:\DISPATCH DDASETUP.ONL Calculation of drift velocity DRGMaker D:\DISPATCH DRGMaker.ini, xxx.UDD Calculation of directogram TILT D:\DISPATCH Tilt.ini, xxx.UDD Calculation of ionospheric tilt Ion2PNG D:\DISPATCH Ion2PNG.ini, xxx.UDD Ionogram image production Sky2PNG D:\DISPATCH Sky2PNG.ini, xxx.UDD Skymap image production Drg2PNG D:\DISPATCH Drg2PNG.ini, xxx.UDD Daily Directogram image production Dvl2PNG D:\DISPATCH Dvl2PNG.ini, xxx.UDD Daily drift plot production 538. Most of the post-processing components read Station ID number from the input file to acquires station constants from the appropriate Station UDD file located in D:\DISPATCH\UDD folder. The Station UDD file is an ASCII text file containing setup parameters which select optional features of the sounder software. Each line in the file may be one of the following entries: PARAMETER LINE (preceded with an asterisk * in column 1) The asterisk is immediately followed by a 3-digit parameter number and its body enclosed within < >). EXTERNAL COMMENT LINE (no special character in column 1) Contains instructions regarding the following parameter line. INTERNAL COMMENT LINE (preceded with a percent sign % in column 1) A comment line invisible to software that reads the file. 539. Details of the file format, including the site specific and system specific setup variables, are provided in Table 5-4. For additional information on the antenna array definitions please refer to Section 2. PARAMETER NAME PARAMETER NO. Table 5-4: Station UDD File UNITS RANGE ACCURACY Section 1 - GEOPHYSICAL PARAMETERS AND SITE INFORMATION PRECISION DATA TYPE FORMAT SECTION 5 SYSTEM SOFTWARE 5-19 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Station Name *304 Descriptive Text String <60 chars URSI Code Site Latitude *307 *101 5 symbols Deg –90 to 90 0.1 String <60 chars 0.1 Real Free 2 Site Longitude *102 Deg East 0 - 359.9 0.1 0.1 Real Free Site Gyrofrequency Site Dip Angle Site Declination *104 *105 *106 MHz Deg Deg 0.5 - 2.0 –90 to 90 –90 to 90 0.1MHz 1 1 0.1 MHz 1 1 Real Free Integer Free Integer Free Section 2 – DIGISONDE MODEL AND ANTENNA CONFIGURATION (refer to Section 2 for details) Digisonde Model *032 Declination of Antenna X axis from Geographic North Pole *079 Units Deg 5 for Digisonde 4D –90 to 90 1 unit 0.1 Integer 0.1 Integer Free Real Free Antenna Positions X coordinates *080 m -34.64 to 0.01 m 0.01 m Real Free +34.64 Antenna Positions Y coordinates *081 m -34.64 to 0.01 m 0.01 m Real Free +34.64 Antenna Positions Z coordinates *082 m -34.64 to 0.01 m 0.01 m Real Free +34.64 Antenna Pattern for *086 Ionogram Displays Units 0,1,2,3 1 unit Integer Integer Integer Antenna Layout Antenna DEVN *090 *091 Units Deg 0,1,2,3,4 1 unit -180 ..+180 0.1 Integer 0.1 Integer Real Integer Free Antenna MAXDIST *092 m <=60 0.01 m 0.01 m Real Free Section 3 – CONTACT INFORMATION Person Name *410 Text String <60 chars Organization *411 Text String <60 chars Address *412 Text String <60 chars Email *413 Text String <60 chars 540. Refer to Section 3 for description and examples of derived data products produced by Digisonde-4D. ARTIST 541. The Automatic Real-Time Ionogram Scaler with True height (ARTIST) is an intelligent system developed at UMLCAR for extraction of ionospheric specification data from ionograms. The automatic ionogram interpretation (“scaling”) is a computer-hard problem that requires a model of human visual perception to extract useful ionogram image signatures and a syntactic analyzer to identify and characterize them. Introduction 2 Format specification "Free" allows the numeric value of the ASCII digits to be converted to the appropriate numeric value 5-20 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL of the ARTIST in the early 1980s was the single most influential advance in the ionospheric sounding technology that had brought the digisonde data outside of a narrow circle of experts into realm of the operational 24/7 space weather systems. 542. INPUT FILES: RSF, SBF. OUTPUT FILES: SAO, SAOXML, MUF. 543. A common approach to the ionogram autoscaling in all ARTIST versions is to (1) adaptively threshold the ionogram image to remove background noise, (2) reduce echoes to edgels (edge elements) corresponding to the leading edge of the echo, (3) string echoes into traces, and (4) identify traces and determine their characteristics. 544. Digisonde-4D are supplied with the version 5 of ARTIST software. Further details on ARTIST-5 algorithms can be found in [Galkin et al., 2007]. Autoscaling Confidence Level (ACL) of ARTIST-5 545. The Autoscaling Confidence Level (ACL) is determined indirectly and automatically by examining the ionogram features and the autoscaling outcome for various anomalies. Such examination of the ARTIST results resembles other software solutions that use multiple criteria to spot commonly observed autoscaling problems, including  high mismatch of the extracted trace with the trace restored from the calculated electron density profile,  unreasonable separation of O- and X-cusps in the F2 echo traces,  excessive frequency gap between E and F layer traces,  unreasonably high variability of the scaled values from ionogram to ionogram. 546. Since the mid-1990s, a two-digit ARTIST “confidence level” value is routinely provided with each autoscaled ARTIST record to help end user applications with automatic accept/reject decisions. Still, independently of the ARTIST development, other post-evaluation algorithms have been developed to characterize and mitigate autoscaling errors. In particular, the USAF QUALSCAN system is used at the DISS Mirrion server in Boulder, CO to tag out those autoscaled records that did not pass QUALSCAN quality criteria. 547. ARTIST-5 software is not only able to check its result using common “sanity checks”, but also to detect anomalies in the ionogram interpretation process itself. For example, if the F2 trace cusp extraction algorithm detects the presence of multiple trace segments that are representing the assumed foF2 cusp, confidence in the correctness of such ionogram evaluation is decreased. Post-evaluation algorithms like QUALSCAN are not able to sense such complications of the interpretation process. ARTIST-5 Ionogram Qualifiers 548. In addition to the ACL value determined by ARTIST-5 by inspecting autoscaling process and its outcome for anomalies, another level of ionogram qualification is provided by automatic classification of each ionogram in terms of the level of the ionosphere/ionopgram disturbance. A total of six ionogram categories is defined for the error analysis by assigning the following ionogram qualifiers: QC = Quiet ionospheric conditions, Confident ARTIST scaling ACL = 1 MC = Moderate Spread F conditions, Confident ARTIST scaling ACL = 1 HC = Heavy Spread F conditions, Confident ARTIST scaling ACL = 1 QL = Quiet ionospheric conditions, Low confidence of ARTIST scaling ACL = 0 SECTION 5 SYSTEM SOFTWARE 5-21 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL ML = Moderate Spread F conditions, Low confidence of ARTIST scaling ACL = 0 HL = Heavy Spread F conditions, Low confidence of ARTIST scaling ACL = 0 549. For certain locations such as Jicamarca (Peru), Gakona (Alaska), or Campo Grande (Brazil), we observed another class of ionograms for which it is impossible to derive any meaningful vertical electron density profile from the ionogram because of extremely heavy spread F conditions. Such class received a separate qualifier EH: EH = Excessively Heavy Spread F conditions, no autoscaling results attempted 550. Using this system of ionogram qualifiers, it is possible to better reflect long-term statistical differences in the ARTIST accuracy by isolating anomalous records that tend to distort the Gaussian error distribution into separate categories for which the long-term accuracy is expected to be worse and likely non-Gaussian. By excluding the outliers from the main categories of the confidently scaled data, their distributions get closer to the Gaussian. Long-term Statistical Evaluation of Digisonde-4D Accuracy 551. The DPS error analysis focuses on the errors introduced by the automatic scaling and assumes correct manual scaling. Clearly the instrumental errors in measuring the virtual heights h’ and the plasma density are small (see below) compared to the errors introduced by the autoscaling. The long-term statistical accuracy of DPS-4D ionogram-derived data is evaluated by calculating error bars for the scaled characteristics and the resulting error boundaries for the EDP. The error bars and boundaries describe the probability that the true value lies within specified bounds placed around the reported automatically derived values. In this approach, the probability is fixed at a particular level acceptable to the user application (e.g., 95%, 1σ, etc.), and the bounds are then determined from statistical comparison of reported (autoscaled) values to the true (manually scaled) values. Once the bounds are determined from the comparison set of ionograms, they are applied to the rest of the data. Such method benefits from ionogram classification into subcategories in which data possess statistically different accuracy. In this case, ARTIST-5 software determines the ionogram subcategory (using the system of ionogram qualifiers) and then applies the appropriate set of error measures to describe its accuracy. Sensitivity study of ionogram-derived data accuracy 552. A full scale study of the ARTIST data was conducted to determine ionogram subcategories that would reveal different levels of accuracy. Close to 250,000 manually scaled digisonde ionograms were involved in the study that tested dependence of the autoscaled errors on location, season, time of day, level of ionospheric disturbance, and autoscaling confidence level. The study results demonstrated clear dependence of the accuracy on the location of the sounder, level of ionospheric disturbance, and ACL. For the purpose of this study, the accuracy was still evaluated for ACL=0 data, and because it indeed appears to be considerably worse, rejecting ACL=0 data from assimilation makes sense. Alternatively, they still could be assimilated, but with large error bars. No visible difference was found in the accuracies calculated for different time periods of the day and seasons. Error bars for autoscaled critical frequencies 553. Figure 5-6 illustrates the approach taken for evaluation of the error bars for the critical frequencies. It shows an example error histogram for the critical frequency of the F2 layer, foF2, obtained for 20,675 manually scaled Průhonice DPS-4 ionograms. The error histogram plots the percent of records as a function of observed error, i.e. the difference between manual and ARTIST values. A negative error means that the autoscaled value is underestimated, and a positive error corresponds to ARTIST overshooting the true foF2. 5-22 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 554. Using the histogram data, we select the percent level (horizontal line in Figure 5-6) so that 95% of all ionograms are contained above it. Corresponding intersections of the 95% percent line with the histogram curve then serve as the lower and upper uncertainty bounds that secure 95% probability for the true value to fall within provided bounds. For the Průhonice DPS-4, such intersection points are -0.45 and +0.15 MHz, so that future autoscaled foF2 values can then be reported with uncertainty bounds of -0.15 to +0.45 MHz. Figure 5-6: Error histogram of autoscaled critical frequencies of F2 layer obtained for 20675 ionograms from DPS-4 ionosonde at Průhonice, Czech Republic. 95% of all autoscaled values lie within the -0.45 to +0.15 MHz interval from the true values provided by manual scalers. 555. Figure 5-7 illustrates the benefits of sorting ionograms in subcategories to statistically capture differences of autoscaling performance for different classes of ionograms. It shows the error histogram built using only ionograms taken during quiet ionospheric conditions and autoscaled with at a high confidence level (ionogram qualifier QC). Comparison of Figure 5-6 and Figure 5-7 shows improvement of the lower error bound enclosing 95% of all data from 0.45 to 0.3 MHz. Remarkably, 81% of all ionograms taken at Průhonice, a typical mid-latitude location, fall in the QC category (quiet ionosphere, confidence scaling). Similar ratio has been observed at other mid-latitude locations. SECTION 5 SYSTEM SOFTWARE 5-23 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 5-7: Error histogram of autoscaled critical frequencies of F2 layer obtained for 16,712 ionograms from DPS-4 ionosonde at Průhonice taken during quiet ionospheric conditions and auto-qualified as high confidence. Lower bound for foF2 error bar specification has improved from -0.45 to -0.3 MHz in com- parison to the all ionogram case shown in Figure 5-6. Error boundaries for EDP 556. Figure 5-8 illustrates the placement of the error boundaries on EDPs derived from the ionograms. Inner and outer boundaries are calculated using two Chebyshev polynomials representing the profile shape that are derived from the original profile coefficients to fit anchor points that are placed at the error bars for the critical frequencies, the valley between E and F regions, and the unknown starting height of the ionosphere. To avoid crossing of the boundaries in the valley region between E and F layers, the inner boundary gets a wider valley width Win and a deeper valley depth Din, and the outer boundary has a narrower valley Wout and shallower depth Dout (see insert in Figure 5-8). 5-24 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 5-8: Autoscaled ionogram from Roquetes, Spain, with inner and outer error boundaries for calculated EDP. The error boundaries are obtained by modifying the original profile coefficients so that the boundary fits the anchor points as indicated. Error bars for foE, foF1. and foF2 critical frequencies are specific to the quiet confident ionograms at Roquetes (95% probability level). Processing Precise Ranging Data in ARTIST 557. The ARTIST-5 software takes advantage of the PR processing in the ionograms that were taken in the PR mode by a technique that verifies consistency of the precise range measurements and interpolates missing values. The technique is illustrated in Figure 5-9 where the ARTIST trace extracted without PR information is shown as the yellow line along the leading edge of the echo trace, and the white line corresponds to the updated h’-trace in which all range values are corrected using available PR data. The PR value calculated for each echo bin is shown as a white number within the bin giving the accurate h’ for this echo. The star symbols indicate PR values that passed consistency criterion and were directly used to update the initial trace derived exclusively from the amplitude information. Diamond shapes show PR values that are inconsistent over the pulse width interval, for which the trace point is adjusted using an average bias of the range evaluated from all consistent PR values. Finally, circle shapes are used to show interpolated trace gaps that are re-interpolated using new trace values. SECTION 5 SYSTEM SOFTWARE 5-25 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 5-9: Precision Ranging processing in ARTIST-5. The original ARTIST trace is shown as the yellow line, and the trace updated with Precision Ranging (PR) data is shown as the white line. Calculated PR values for each echo bin are shown as white numbers within the bin. When PR values are consistent over abutting range bins for the same frequency, their value (shown as white stars) is used to replace the conventional range directly. DFT2SKY 558. DFT2SKY uses drift measurements to identify angle of arrival for all reflected signals (“sources”) observed in the data. The angles are then plotted as dots on a ‘Doppler skymap’ in which center of the plot corresponds to the vertical direction, the radial distance from the plot center represents the zenith angle, and the azimuthal angle is counted clockwise with the top of the plot corresponding to the North direction. 559. INPUT FILE: DFT. OUTPUT FILE: SKY DDAV 560. DDAV uses skymaps to calculate the full three-dimensional plasma drift vector in the assumption that the plasma moves uniformly within the field of view of the digisonde. 561. INPUT FILE: SKY. OUTPUT FILE: DVL TILT 562. TILT uses skymaps to calculate the offset of the center of skymap sources from the zenith, i.e., the overall tilt of ionospheric isodensity contours at the sounder location. 563. INPUT FILE: SKY. OUTPUT FILE: TLT DRGMAKER 5-26 SECTION 5 SYSTEM SOFTWARE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 564. DRGMAKER uses ionograms with directional information to calculate directograms as described in Section 3. 565. INPUT FILE: RSF. OUTPUT FILE: DRG ION2PNG 566. ION2PNG produces image of ionograms with superimposed scaled ionospheric characteristics, electron density profile (EDP), error boundaries for the EDP, and MUF table. 567. INPUT FILE: RSF, SAOXML. OUTPUT FILE: PNG SKY2PNG 568. SKY2PNG produces image of the Doppler skymap with superimposed calculated drift velocity and included zenith and azimuth angles of ionospheric tilt. 569. INPUT FILE: SKY, DVL, TLT. OUTPUT FILE: PNG DRG2PNG 570. DRG2PNG produces image of the daily directogram. 571. INPUT FILE: DRG (daily file). OUTPUT FILE: PNG DVL2PNG 572. DVL2PNG produces image of the daily plot of drift velocities in the ionosphere. 573. INPUT FILE: DVL (daily file). OUTPUT FILE: PNG SECTION 5 SYSTEM SOFTWARE 5-27 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL ANNEX A DESC TO DCART INTEFACE CONTROL DOCUMENT COMMON DEFINITIONS Structured data Structured Data or, simply, Structure is the ordered collection of fields. Field Field is either  Primitive Field,  Structure (a collection of Fields),  Array of Primitive Fields, or  Array of Structures. No memory gaps are present between the Fields in a Structure, i.e. all Fields start immediately after the end of the previous Field. The first Field of a Structure starts at the memory address of the Structure. Thus, values of Fields in the Structure can be uniquely obtained as soon as its memory address is known. Field descriptions are given as a table in which rows are fields of structured data and columns are common characteristics of these fields. Common characteristics of the Field are given in Table 5A-5-5. Name BYTE OFFSET BYTE LEN MNEMONIC DESCRIPTION UNITS TYPE RANGE Table 5A-5-5: Characteristics of Field Description Byte offset from the start of structure Length in bytes Short name. This name must be unique within structure this field belongs to. Verbal description Physical units For primitive field we use notation shown below in Section 1.3.2. For structured field we can mention its structure name or table number that describes corresponding structure. Legal range of values. Used for primitive fields. Primitive field types Column ‘type’ in many tables describing fields of various structured data will mean all necessary things you need to extract field value from memory. Common primitive data types used in this document are listed in Table 5A-5-6. Table 5A-5-6: Primitive field types Abbreviation Byte Len Description INT8U 1 INT8S 1 8 bits unsigned 8 bits signed A5-1 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL INT16U INT16S INT32U INT32S INTU ACD INTS ACD 2 2 4 4 Variable, 1 – 15 16 bits unsigned 16 bits signed 32 bits unsigned 32 bits signed Unsigned integer represented as ASCII Coded Decimal Each decimal digit of integer number takes one byte of external memory and its ASCII code will be saved there. If length of the field is larger than length of bytes occupied by integer number then this number has to be shifted to the right edge of the field and has to be padded either by ASCII code of ‘0’ or ASCII code of SPACE. Variable, 1- 15 Signed integer represented as ASCII Coded Decimal Each decimal digit of integer number takes one byte of external memory and its ASCII code will be saved there. ASCII code of sign can be saved as first byte. If length of the field is larger than length of bytes occupied by integer number then this number has to be shifted to the right edge of the field and has to be padded either by ASCII code of ‘0’ or ASCII code of SPACE. Any of these basic types can be used to construct an array, for example, INT8U array. COMMON PACKET FORMAT Generally, all DPS V6 packets consist of the following 5 sections (Table 5A-5-7):  Sync Pattern, used for frame synchronization in the lossy communication environments. Sync pattern for DPS V6 is 3 byte sequence 0xFEFA313.  Length (byte count of the packet contents, including all packet elements from sync pattern to the checksum)  Packet Type, used to distinguish it from other packets requiring different actions  Packet Data (Data Section of Packet)  Checksum (XOR of all bytes in the packet) Length, Packet Type and Packet Data constitute the packet Payload. Byte Byte Offset Len 0 3 Mnemonic SYNC 3 2 LENGTH 5 1 TYPE 6 Variable DATA Last 1 CS Table 5A-5-7: Common Packet Format Description Units Sync Pattern - 0xFE, 0xFA, 0x31 Length of packet including SYNC, LENGTH, TYPE, byte DATA, and CS Type of packet - Packet Data byte Checksum byte Type INT8U Range Constant INT16U 0..65535 INT8U INT8U array INT8U 0..255 0..255 COMMON DATA ELEMENTS Measurement Program Measurement program, or simply Program, is a set of parameters that uniquely specify particular measurement taken by the DPS. All Program types have the same first field, “Operation Code” (OpCode), that is followed by Operation, a specific structure of parameters defining the DPS operation. DPS keeps an array of 128 Program 3 FEFA30 header is used for RPI, and FEFA32 header is used for TNT. A5-2 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL specifications in memory. There are four kinds of Programs, each having different OpCode and Operation structure: 1. Empty Operation (OpCode = 0) is a no-action operation. It is used to label unused entries in the array of Programs. If DESC is commanded to run an Empty Operation, it generates an error message. The Operation structure of this command is empty. 2. Sounding Operation (OpCode = 1) represents the most commonly used measurement mode of the DPS when DESC commands hardware to transmit signals and sample antenna voltages. The Ionogram and Drift measurements both fall into this category. 3. Built-in Test Operation (OpCode = 2) is a housekeeping mode of DPS operations in which DESC collects sensor data in various modes to diagnose condition of the Digisonde hardware. This test returns result data, which is useful for engineers and also can be used by DCART for sending alert messages. 4. Channel Equalizing operation (OpCode = 3) represents operational mode in which DPS is configured to send an attenuated transmitter signal to Antenna Switch to determine amplitude and phase differences between four receiver channels. When DESC or DCART software need to interpret one Program object, they read the Operation Code first, and then they have enough information to appropriately unpack the rest of the Operation structure. Empty Program Table 5A-5-8 contains description of the Empty Program. Table 5A-5-8: Empty Program Specification (length 1 byte) Byte Byte Mnemonic Offset Len Description Units Type 0 1 OP_CODE Operation code. Contains constant 0. - INT8U Range 0 Sounding Program The Sounding Program has the largest number of user-selected parameters in its Operation structure. The parameters can be divided in three sections:  Operation Option  Common Specification of the sounding measurement  Data Processing Selection: o All processing steps that have to be applied to raw data o Processing steps that preferably to be applied by DESC, - these processing steps matched to some starting subsequence of all processing steps Operation Option is used to describe whether digisonde produces actual measurement data or simulates one of available test patterns. Common Specifications define all parameters that are common to both ionogram and drift mode of digisonde operations. This part includes, for example, frequency and range stepping, number of pulses per frequency, signal waveform, etc. Common Specifications determine how the time domain data are collected by the DESC and forwarded to DCART. A5-3 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL There is a variety of Data Processing that both DESC and DCART can apply to the collected time domain data in order to produce the final data product to be archived (i.e., an ionogram or a drift measurement). Number and sequential order of the processing steps that are required to derive the final DCART data product from the raw time domain data depend on:  choice of data product (i.e., ionogram, drift record, or intermediate step data),  choice of DPS signal waveform, and  optional processing, such as the RF Interference Mitigation (RFIM). The variety of processing steps and processors that execute them is described in terms of one linear sequence of Data Process Steps, called Process Chain. The Process Chain has the following properties:  Data Process Steps in the chain are applied successively to the raw time domain data  The complete Process Chain has the following sequence of 5 process steps 0. Raw data (no processing applied) 1. Pulse Compression 2. Sum of complementary code sequences 3. Doppler Processing 4. Ionogram Calculation  Process Chain can be made shorter to produce intermediate step data, but only by removing steps from the end of the chain.  Each step in the Process Chain can have any number of optional unchained process steps attached to its output. The main Process Chain can be described by one byte, the ID of the last data process step (0 to 4). Selection of the unchained steps can be described by one byte, where each bit corresponds to the one of the available unchained steps. Currently two unchained steps are provided, 0x1. Channel Equalizing (CEQ), applied at the output of chained step 0 0x2. RFI Mitigation, applied at the output of chained step 0 Therefore, the following settings of the unchained step selection are possible: 0 = no unchained steps called, 1 = Channel EQ 2 = RFI Mitigation, 3 = both RFIM and Channel EQ. Table 5A-5-9 shows specification of the Data Processing structure. Byte Byte Offset Len Table 5A-5-9: Data Processing structure (length 2 bytes) Mnemonic Description Units Type Range A5-4 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 0 1 CHAINED_PROC Chained process step to be applied: - 0 = Do not process (raw data) 1 = Pulse compression 2 = Sum complimentary 3 = Doppler calculation 4 = Ionogram calculation Note: temporarily constant, set to Do not process 1 1 UNCHAINED_PROC Bit-mask for unchained process steps to be applied. - 0x1 = Channel EQ 0x2 = RFI mitigation INT8U 0…4 INT8U 0 .. 3 Table 5A-5-10 contains description of the Sounding Program. The Common Specification section of the sounding program definition is highlighted in blue. Parameters that are ignored by DESC are highlighted in yellow. Table 5A-5-11 describes contents of the Flexible Frequency List (“flex-list”), which is used for specification of varying number of arbitrary operating frequencies for the sounding operation. Byte Byte Offset Len 0 1 1 1 2 2 4 2 6 bits: 0-3 Table 5A-5-10: Sounding Operation (variable length) Mnemonic Description Units OP_CODE OP_OPTION ALL_PROC Operation code. Contains constant 1 (Sounding). Operation option: - 0 = Measurement 1 = Internal loopback 2 = HW (digitizer card hardware) test pattern 3 = SW (software) test pattern All data processing steps desired to be applied to raw data - DESC_PROC Processing desired to be done prior to delivery of data to DCART. This Data Processing is equal to some incom- plete part of ALL_PROC or to the whole ALL_PROC. Notes: Although DCART can run all processing steps described by ALL_PROC, these steps can be delegated, partially or com- pletely, to the digisonde hardware and the embedded com- puter system, thus relieving DCART from some of the work to be done. It is possible to control where particular process- ing steps occur by specifying DESC_PROC. Data Processing that has really been applied by DESC is reflected in corresponding field of Data Preface structure and it should not exceed Data Processing described by this field. FILE_FORMAT File format that will be used for final product data file after - applying all processing steps defined by ALL_PROC. The following file data format options are available: 0 – Generic Format. This format exists for any kind of data as Raw Data, Doppler Data, Ionogram Data 1 – DFT format. Only for Doppler Data 2 – RSF format. Only for Ionogram Data Note: this field is ignored by DESC Type INT8U INT8U Range 1 - Data Proc- N/A essing structure Data Proc- N/A essing structure INT4U 0, 1, 2 A5-5 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Byte Byte Offset Len bits: 4-7 7 2 9 2 11 2 13 1 14 1 15 1 16 2 18 2 20 1 21 1 22 1 23 1 24 1 25 1 Mnemonic BIN_FORMAT L U FF FFR FST FLS CFS FFS NFS MX M W IPS TM Description Units Type Databin format. It is defined only for Generic format, in which case the databin format number is: a). For Raw or Time Domain data type 0 - uncompressed 1 - compressed b). For Doppler data type 0 - uncompressed 1 - compressed c) For Ionogram data type 0 - all-antennas uncompressed 1 - all-antennas compressed 2 - antenna-convolved uncompressed 3 - antenna-convolved compressed 4 - antenna-convolved very compressed Lower Frequency Limit This field’s used when Frequency Stepping Law is Linear or Logarithmic Upper Frequency Limit This field’s used when Frequency Stepping Law is Linear or Logarithmic Fixed Frequency This field’s used when Frequency Stepping Law is Fixed Frequency Fixed Frequency Repeats This field’s used when Frequency Stepping Law is Fixed Frequency Frequency Stepping Law 0 = Linear 1 = Logarithmic 2 = Fixed Frequency (Lower Frequency Limit value is used) 3 = Flex List (user-defined list of operating frequencies) Flex List Size Size of Flex List (number of user-defined frequencies). This field’s used when Frequency Stepping Law is Flex List. Coarse Frequency Step This field’s used when Frequency Stepping Law is Linear or Logarithmic Fine Frequency Step - 1 kHz 1 kHz 1 kHz - 1% (log) 1 kHz (lin) 1 kHz INT4U INT16U INT16U INT16U INT8U INT8U INT8U INT16U INT16U Number of fine steps - Fine step multiplexing - 0 = no multiplexing 1 = multiplexing Multiple frequency operation (constant, set to single fre- - quency mode) 0 = single frequency mode 1 = dual frequency mode 2 = quadruple frequency mode Waveform - 1 = 16-chip complimentary code 2 = 67 s short pulse Interpulse phase switching (constant, set to disabled) - 0 = disabled 1 = enabled Transmitter mode - 0 = off 1 = on INT8U INT8U INT8U INT8U INT8U INT8U Range 1000 kHz 30000 kHz 1000 kHz 30000 kHz 1000 kHz 30000 kHz 0..255 0,1,2,3 0..255 1-100% 1 kHz1MHz 1 kHz1MHz 1..8 0, 1 0, 1, 2 1, 2 0, 1 0, 1 A5-6 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Byte Byte Offset Len 26 1 27 1 28 1 29 1 30 2 32 2 34 1 35 1 36 1 37 1 38 1 Mnemonic A POL N IPP START_RANG E END_RANGE Description Antenna option (constant, set to multi-beam processing) 0 = sum of all 4 antennas 1 = antenna 1 2 = antenna 2 3 = antenna 3 4 = antenna 4 7 = multi-beam processing Polarizations 0 = O only 1 = X only 2 = O and X Number of Integrated Repeats (excluding code pairs and polarizations) Inter-Pulse Period Start Range End Range RANGE_STEP Range Step CG RX_G AGC AUTO_DRIFT Constant Gain In OP_OPTION = Measurement 0 = full gain 1 = -9 dB in Antenna Switch 2 = -9 dB in Tracker 3 = -18 dB in Tracker and Antenna Switch In OP_OPTION = Internal loopback 0 = full gain 1 = -9 dB in Antenna Switch 2 = -18 dB in Tracker and Antenna Switch 3 = -35 dB in Tracker and Antenna Switch Rx Gain 0 = +30 dB 1 = +24 dB 2 = +18 dB 3 = +12 dB 4 = +6 dB 5 = 0 dB 6 = -6 dB 7 = -12 dB Automatic gain control 0 = fixed gain 1 = create gain table before sounding program and use it 2 = use existed gain table 3 = use trial pulses on each frequency Auto-Drift frequency commanding 0 – disabled 1 – enabled If enabled: Frequency Stepping Law must be – 2 (Fixed Frequency) See also: Auto-drift Message Packet Units - Type INT8U Range 0, 1..4, 7 - INT8U 0, 1, 2 2N INT8U 3..7 5ms INT8U 1.25 INT16U 0..1023 km 1.25 INT16U 0..1023 km 1.25 INT8U 2 km - INT8U 0, 1 6 dB INT8U 0..7 - INT8U 0, 1,2 - INT8U 0, 1 A5-7 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Byte Offset 39 40 42 44 45 49 50 51 57 Byte Mnemonic Len 1 SAVE_DATA_F 2 TOP_RANGE 2 BOT_RANGE 1 NRO 4 PULSE_SEQ 1 DELAY 1 DIG_MODEL 6 TX_ID FLS * FL 2 Description Units Save Data Flags Bit 0 Save Raw Data flag Bit 1 Do Not Save Product Data Bit 2 Ionogram Data Reduction, when set then databins with amplitudes ≤ MPA will be lost Notes: DCART has a global option that can override Save Raw Data flag selection to produce no raw files or produce raw files for all available programs. Option ‘Do not Save Product Data’ is used for testing and some cases when you do not need to save produced data Top Range of the search window for the strongest echo Search window is used to select a subset of ranges (see NRO) around the strongest echo (199 E-layer, 400 F-layer) Presently this parameter is used only by Doppler processing when creating Doppler/Drift data product. See also: Auto-drift Message Packet Bottom Range of the search window for the strongest echo Search window is used to select a subset of ranges (see NRO) around the strongest echo (80 E-layer, 200 F-layer) Presently this parameter is used only by Doppler processing when creating Doppler/Drift data product. See also: Auto-drift Message Packet Number of Ranges to Output (reduced number of ranges selected around the strongest echo on each frequency) Presently this parameter is used only by Doppler processing when creating Doppler/Drift data product. Set this parameter to 0 if you want all ranges to be output Order of Pulse Sequencing: list of 4 IDs from the slowest changing to the fastest changing index within one CIT. Available IDs are: 0 = Fine Frequency 1 = Polarization 2 = Integrated Repetition 3 = Complementary Code Sampling Start Delay In support of oblique sounding mode Shall be specified in increments of 5 msec (1500 km) Digisonde model from UDD 3 = DPS-4 5 = DPS-4D Transmitter ID In support of oblique sounding and Tx surveillance modes For oblique sounding experiments with other DPS transmitters, TX_ID is 000XXX, where XXX is Station ID. For not oblique sounding this field is equal to ‘ ‘ (6 space characters). 000000 means UNKNOWN station Flex List Frequencies (Table of Frequencies, Table 5A-5-11) - 1.25 km 1.25 km - - 5 msec - kHz Type INT8U INT16U INT16U INT8U INT8U array INT8U INT8U INT8U array INT16U array Range 0, 1 0..1023 0..1023 1, 2, 4, 8, 16, 32 0..255 Text - Byte Byte Offset Len 0 2 Table 5A-5-11: Frequency for Flex List (length 2 bytes) Mnemonic Description Units Type FR Frequency, element of Flex List Frequencies array kHz INT16U Range 1000 kHz – 30000 kHz Built-In Test Operation Table 5A-5-12 contains description of the Built-in Test Program. A5-8 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Table 5A-5-12: Built-in Test Operation (length 4 bytes) Byte Byte Offset Len Mnemonic Description Units 0 1 OP_CODE Operating code. Contains constant 2. 1 1 OP_OPTION Operation option: - 0 = Measurement 1 = SW (software) test pattern 2 2 FREQ Frequency Run BIT on this frequency 1 kHz Type INT8U INT8U INT16U Range 2 0,1 1000 kHz 30000 kHz Cross-Channel EQ Operation Table 5A-5-13 contains description of the Channel EQ Program. Byte Byte Offset Len 0 1 1 1 2 2 4 2 6 2 8 2 10 2 12 1 13 1 14 1 15 1 16 1 Table 5A-5-13: Channel Equalizing Operation (29 bytes) Mnemonic Description Units Type Range OP_CODE OP_OPTION ALL_PROC DESC_PROC L U CFS W IPS POL N IPP Operating code. Contains constant 3 (Channel EQ). Operation option: 0 = Measurement 1 = Internal loopback 2 = HW (digitizer card hardware) test pattern 3 = SW (software) test pattern All data processing steps applied to acquired sample data. Processing done prior to delivery of data to DCART. Notes: Although DCART can run all processing steps described by ALL_PROC, these steps can be delegated, partially or completely, to the digisonde hardware and the embedded computer system, thus relieving DCART from some of the work to be done. It is possible to control where particular processing steps occur by specifying DESC_PROC. Data Processing that have been applied by DESC will be reflected in corresponding field of Data Preface structure and it will not exceed Data Processing described by this field. Lower Frequency Limit This field’s used when Frequency Stepping Law is Linear or Logarithmic Upper Frequency Limit This field’s used when Frequency Stepping Law is Linear or Logarithmic Coarse Frequency Step This field’s used when Frequency Stepping Law is Linear or Logarithmic Waveform 1 = 16-chip complimentary code 2 = 67 s short pulse Interpulse phase switching (constant, set to disabled) 0 = disabled 1 = enabled Polarizations 0 = O only 1 = X only 2 = O and X Number of Integrated Repeats (excluding code pairs and polarizations) Inter-Pulse Period - - 1 kHz 1 kHz 1% (log) 1 kHz (lin) 2N 5ms INT8U INT8U Data Processing structure Data Processing structure INT16U INT16U INT16U INT8U INT8U INT8U INT8U INT8U 3 0,1,2,3 N/A N/A 1000 kHz 30000 kHz 1000 kHz 30000 kHz 1-100% 1 kHz1MHz 1, 2 0, 1 0, 1, 2 3..7 A5-9 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Byte Byte Offset Len 17 2 19 2 21 1 22 1 23 1 24 1 25 4 Mnemonic START_RANGE Start Range Description END_RANGE End Range RANGE_STEP Range Step CG Constant Gain In OP_OPTION = Measurement 0 = full gain 1 = -9 dB in Antenna Switch 2 = -9 dB in Tracker 3 = -18 dB in Tracker and Antenna Switch Units 1.25 km 1.25 km 1.25 km - RX_G AGC PULSE_SEQ In OP_OPTION = Internal loopback 0 = full gain 1 = -9 dB in Antenna Switch 2 = -18 dB in Tracker and Antenna Switch 3 = -35 dB in Tracker and Antenna Switch Rx Gain 6 dB 0 = +30 dB 1 = +24 dB 2 = +18 dB 3 = +12 dB 4 = +6 dB 5 = 0 dB 6 = -6 dB 7 = -12 dB Automatic gain control - 0 = fixed gain 1 = create gain table before sounding program and use it 2 = use existed gain table 3 = use trial pulses on each frequency Order of Pulse Sequencing: list of 4 IDs from the slowest - changing to the fastest changing index within one CIT. Available IDs are: 0 = Fine Frequency 1 = Polarization 2 = Integrated Repetition 3 = Complementary Code Type INT16U Range 0..1023 INT16U 0..1023 INT8U 2 INT8U 0, 1 INT8U 0..7 INT8U 0, 1,2 INT8U array Tracker Calibration Table 5A-5-14 contains description of the Trackers Calibration Program. Byte Byte Len Off- set 0 1 1 1 Table 5A-5-14: Trackers Calibration Operation (29 bytes) Mnemonic Description Units Type OP_CODE OP_OPTION Operating code. Contains constant 4. 0 = Measurement 1 = Internal loopback 2 = SW (software) test pattern INT8U - INT8U Range 4 0,1 A5-10 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 2 1 CG Constant Gain - In OP_OPTION = Measurement 0 = full gain 1 = -9 dB in Antenna Switch 2 = -9 dB in Tracker 3 = -18 dB in Tracker and Antenna Switch 3 1 4 1+ 4 * BND_QTY Byte Offset 0 1 Byte Len 1 structTruckerBandLength * BND_QTY In OP_OPTION = Internal loopback 0 = full gain 1 = -9 dB in Antenna Switch 2 = -18 dB in Tracker and Antenna Switch 3 = -35 dB in Tracker and Antenna Switch RX_G Rx Gain 6 dB 0 = +30 dB 1 = +24 dB 2 = +18 dB 3 = +12 dB 4 = +6 dB 5 = 0 dB 6 = -6 dB 7 = -12 dB TR_BANDS Trackers Bands structure (see Table 5A-5-15) - Table 5A-5-15: Trackers Bands (variable length) Mnemonic Description Units BND_QTY BANDS Number of trackers bands - Array of Trackers Bands (see Table 5A-5-16) - Elements should be in increasing order of Start Trackers and without duplicating them. Byte Byte Offset Len 0 2 Mnemonic START_FREQ 2 2 STEP_FREQ 4 1 HW_CMD Table 5A-5-16: Tracker Band (length 5 bytes) Description Units Start of Tracker Band. kHz Note: There is no End of Tracker Band in this structure, but having in mind this structure is used only as an element of array, the End of Tracker Band is equaled to the Start Frequency of next element in array. Step inside band. kHz All tuning frequencies in the band are given as follows: 1st tuning frequency is equal to START_FREQ, 2nd tuning frequency is equal to 1st + STEP_FREQ, 3rd tuning frequency is equal to 2nd + STEP_FREQ, etc. up to, but not including, the End of Band Note: Value 0 means that START_FREQ is the only tuning fre- quency in the band Commanding byte to select band - INT8U INT8U structure Type INT8U structure Type INT16U INT16U INT8U 0, 1 0..7 Range 1…255 Range 1…65535 0…65535 0..255 Time Stamp Time stamps are provided in UT with precision of 1 ms. Table 5A-5-17 describes common presentation of the time in the DPS packets (totaling 17 bytes). Byte Byte Offset Len Mnemonic Table 5A-5-17: Time Stamp (length 17 bytes) Description Units Type Range A5-11 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 0 4 4 2 6 2 8 2 10 2 12 2 14 3 YR MON DAY HR MIN SEC MS Year: YYYY Month: MM Day of month: DD Hour: HH Minutes: MM Seconds: SS Milliseconds: Sss Year INTU ACD - Month INTU ACD - Day INTU ACD - Hour INTU ACD - Minute INTU ACD - Second INTU ACD - Milli- INTU ACD second Schedule Measurement schedule, or simply schedule, describes sequence of program, up to 32 entries, running with relative time offset from the schedule start time. Schedule specification is a common part of commanding streams. Schedule contents are described in Table 5A-5-18 and schedule entry structure in Table 5A-5-19. Important Note. If Number of Entries, which is the first element of schedule, is zero then Duration and Entry Table are omitted from Schedule, so that empty Schedule occupies just 1 byte Byte Byte Offset Len 0 1 Mnemonic ETS Table 5A-5-18: Schedule (variable length) Description Units Entry Table Size, i.e. number of entries in Entry Table - If equals to 0 then DUR field is omitted. 1 5 Byte Offset 0 1 4 DUR ETS x 5 ET Schedule duration 0 = immediate iteration after the last program of the schedule completes >0 = duration Entry Table, consists of Schedule Entries (see Table 5A-5-19: ) msec - Table 5A-5-19: Schedule entry (length 5 bytes) Byte Mnemonic Len Description Units 1 PRN Program Number - 4 OFF Offset from the schedule beginning msec -1 = run immediately after previous program is done Type INT8U INT32U Range 0-32, 0 means empty schedule if duration is also 0, otherwise it is Idle schedule 0-4G ms, or 0-1192 hours, or 50 days Array of Schedule Entries Type INT8U INT32S Range 1 – 255 0-2G ms, or 0-596 hours, or 25 days Housekeeping Header Housekeeping Header structure is included in housekeeping packets, such as “I’m alive”, Event Message, Error Message. Table 5A-5-20: Housekeeping Header (length = 39) Byte Byte Offset Len 0 3 Mnemonic DESC_VERSION Description DESC Release Version Units - Type Range A5-12 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 3 1 OP_STATE Operation State: - 1 = Standby 2 = Diagnostic 3 = Scheduled Operations 4 17 TIME_STAMP System clock time - 21 17 TOP_SST Top SST in the SST queue - 38 1 TOP_SCHED Top schedule number in the SST queue - INT8U 1, 2, 3 Table 5A-5-17: Table 5A-5-17: INT8U N/A N/A 0 … 64 Restricted Frequency Interval List Restricted Frequency Interval List is a set of intervals of frequencies forbidden to transmit. Restricted Frequency Interval List contents are described in Table 5A-5-21 and Table 5A-5-22. Byte Offset 0 1 2.. 2 + RFI*N_D 2 + RFI*N_D +1 Byte Len 1 1 RFI * N_D 1 RFI *N_I Byte Byte Offset Len 0 2 2 2 Table 5A-5-21: Restricted Frequency Interval List (variable length) Mnemonic Description Units Type RFIL_VER N_D RFIL Version of RFIL - Number of Restricted Frequency Intervals for Doppler - Restricted Frequency Interval List (Restricted Frequency - Intervals structure, see Table 5A-5-22) INT8U INT8U RFI array Range >0 0 – 255 - N_I Number of Restricted Frequency Intervals for Ionogram - INT8U 0 – 255 RFIL Restricted Frequency Interval List (Restricted Frequency Intervals structure, see Table 5A-5-22) RFI array - Table 5A-5-22: Restricted Frequency Interval (length 4 bytes) Mnemonic Description Units Type SRFI ERFI Start of Restricted Frequency Interval End of Restricted Frequency Interval kHz INT16U kHz INT16U Range 1 kHz – 30000 kHz 1 kHz – 30000 kHz SCIENCE DATA PACKETS Science Data considerations Science Data that produced by running some Sounding Program are called Measurement. From the general point of view, Measurement characterized by Location, Time, Program, and Applied Processes List and contains scientific data that was taken at these location and time by implementing this Program and then have been processed further by applying all the processes in the Applied Processes List. Each Measurement data are produced by running some Program that sends, using transmitter, a series of “Pulses” with specified interval between them. After any Pulse transmitted and before next Pulse, Program samples incoming signal many times producing Raw Science Data. Say, Raw Science Data are Science Data without any process applied to them. So we can see that Raw Science Data grouped by Pulses. Further Raw Sciences Data undergo several known processes. Here are most popular of them given in the sequence of applying: 1. Channel Equalizing, mandatory. No data reduction. 2. RFI mitigation, recommended but may be omitted. No data reduction. A5-13 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 3. Pulse compression if applicable. No data reduction. 4. Sum complementary codes if applicable. Data are reduced by two times. 5. Regrouping by frequencies and calculation of Dopplers. No data reduction. 6. Ionogram calculation: i. Choosing the strongest (having maximum amplitude over all antennas) Doppler for each height. ii. Calculating angle of arrival for strongest Doppler. iii. For each height (for both ordinary and extraordinary data), leaving only, Doppler value itself, average amplitude over antennas of strongest Doppler, and angles of arrival. We see that Science Data are grouped either by Look (=Pulse) or by Frequency so we can say about Look or Frequency Groups, or simply Groups, where each Group has one Group Header (containing information unique to this Group) and calculated, using Program and Applied Processes List, number of Databins. Science Data are grouped by Pulse up to step 4 and grouped by Frequency after step 4. Measurement size is big enough to fit into one or several packets. Usually hundreds or thousands of packets are needed to transmit data from DESC to DCART. One measurement may often exceed 100MB. So DESC, at the time of producing Measurement data, makes packets of this data and sends them to DCART. Having this in mind and the fact that even Frequency Group is big enough to fit into one packet, next section will be clearer for understanding. Science Data Packet structure, packet type 0x81 The following is true. 1. Each Science Data packet includes only part of measurement. 2. All packets of the same measurement are enumerated starting from 1 and this number is called Serial Number of packet. 3. Packet may contain one or more Groups. 4. Packet may contain fractional part of Group. 5. Packet may contain not integral number of Groups. 6. Group may be split between packets. 7. Every packet duplicates some information (for example, Program), which is necessary to be interpreted even if not all packets of measurement reach DCART. The data section of the science data packets contains the following parts:  DESC Release Version, Table 5A-5-23  Science Data Packet General Header, Table 5A-5-24, holding information related to the data packaging technique, A5-14 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL  Preface, Table 5A-5-25, containing Program structure (which is the exact copy of Program that has been used by DESC for generating this measurement), Time Stamp of start of measurement, Data Processing applied to the data so far, and some other information.  Group o Group Header, Table 5A-5-26, repeated for each group o Databins Major Release Version Table 5A-5-23: DESC Release Version, length 3 byte Byte Byte Offset Len Mnemonic Description Units 0 1 DESC_MAJ_VER DESC Major Version - 1 1 DESC_MIN_VER DESC Minor Version - 2 1 DESC_BLD_VER DESC Build Version - Type INT8U INT8U INT8U Range 0 … 255 0 … 255 0 … 255 Science Data Packet General Header Table 5A-5-24: Science Data Packet General Header, length 15 Byte Byte Offset Len Mnemonic Description Units 0 4 SER_NUM_PACKET Serial Number of Packet within the measurement, - counting from 1 4 4 GROUP_INDEX Group Index of the first Group in packet. - All Groups are indexed starting from 0 8 1 N_GROUPS Number of Groups in packet - 9 4 SER_NUM_DATABIN Serial number of the first databin in the first Group, - Counting from 1 13 2 N_DATABINS Number of Databins in the last Group - Type INT32U INT32U INT32U INT32U INT32U Range >0 1 … 255 >0 1 … 65535 Packet Preface Byte Byte Offset Len 0 17 17 1 18 1 19 2 21 LEN Table 5A-5-25: Packet Preface Specification, length variable Mnemonic Description Units Type Range TIME_STAMP Time Stamp of start time (Table 5A-5-17: ) - SCH_NUMBER Schedule Number (0 means manual start of sounding) - PROG_NUMBER Program Number - PROC_APPLIED Data Processing applied to data so far - PROG Program Specification (see Table 5A-5-10 to Table 5A-5-13) TS INT8U INT8U Data Processing structure - 0…255 1…255 N/A - Packet Group Header Byte Offset 0 4 Table 5A-5-26: Packet Group Header, length 6 (12 for debugging) Byte Mnemonic Len Description Units 4 TIME_OFFSET Time Offset of Frequency sounding from measure- ms ment start time (ST) 1 RESTR_FLAG Restricted Frequency Flag (0 – not restricted, 1 – - restricted) Type INT32U INT8U Range 0 to 4,294,967,296 ms or approx. 50 days 0, 1 A5-15 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 5 1 AS 6 2 MAX 8 2 FREQ 10 1 POL 11 1 CODE Attenuation Selection - Notes: 1. It is value commanded to Rx gain control. 2. Attenuation selection does not include Constant Gain (from Program) Absolute maximum value Re or Im data (saturation) - 12 bit – DPS-4S 14 bit – DPS-4D 4Frequency kHz 5Polarization (Ordinary – 0, Extraordinary – 1) - 6Complementary Code Number: - -1 - Code is undefined for this program 1 - Code 1 2 - Code 2 INT8S 0 … 7 INT16U INT16U INT8U INT8S 12 bit – 0… 2048, saturation 2049 14 bit – 0 … 8196 saturation 8197 16 bit – 0 … 32536 saturation 32537 100 to 30000 kHz 0, 1 -1, 1, 2 Databins We consider three types of Databins, Raw Databin, Doppler Databin, and Ionogram Databin. Raw Databin is one quadrature sample, so it is equivalent to pair of numbers, which constitute one complex number and described in Error! Reference source not found.. Doppler Databin is the piece of information that is used in Ionogram Data Structure and pertained to specified frequency, polarization, height, antenna, and Doppler. Doppler Databin described in Table 5A-5-28. Ionogram Databin is the piece of information that is used in Ionogram Data Structure and pertains to specified frequency, polarization and height. Ionogram Databin described in Table 5A-5-29, Table 5A-5-30, and Table 5A-5-31. The program specification and Process Applied determine Databin’s layout and total number of databins collected in one Group. So, there are several cases. A. Raw Data Structure For Raw data, data after RFI Mitigation or data after Pulse Compression have absolutely the same structure and we call this structure Raw Data Structure. The following is true for this structure. 1. Group is Look 2. Layout inside of Look: two dimensional array of Raw Databins, where the first dimension is Number of Antennas and the second dimension is Number of Heights to Sample, or shortly ‘Number of Antennas’ x ‘Number of Heights to Sample’ 3. Layout of Data without fine frequencies multiplexing: five dimensional array of Looks, where a) 1st dimension is Number of Coarse Frequency Steps b) 2nd dimension is Number of Fine Frequency Steps 4 This is temporary field. It is used only for debugging 5 See previous note 6 See previous note A5-16 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL c) 3rd dimension is Number of Integrated Repeats d) 4th dimension is Number of Polarizations e) 5th dimension is Number of Codes 4. Layout of Data with fine frequencies multiplexing: five dimensional array of Looks, where a) 1st dimension is Number of Coarse Frequency Steps b) 2nd dimension is Number of Integrated Repeats c) 3rd dimension is Number of Fine Frequency Steps d) 4th dimension is Number Polarizations e) 5th dimension is Number of Codes B. Summed Complementary Data Structure We have this Data Structure after Sum Complementary process. It is absolutely the same structure as Raw Data Structure except just one thing, Layout of Data has only 4 dimensions as Code dimension disappeared. C. Doppler Data Structure We have this Data Structure after Doppler Calculation process. The following is true for this structure. 1. Group is Doppler Frequency Group 2. Layout inside of Doppler Frequency Group: four-dimensional array of Doppler Databins, where a) 1st dimension is Number of Polarizations b) 2nd dimension is Number of Heights to Sample. It is equaled to Number of Ranges if measurement program parameter NRO (Number of Ranges to Output) is zero, otherwise it is equaled to NRO. c) 3rd dimension is Number of Antennas d) 4th dimension is Number of Dopplers (= Number of Integrated Repeats) 3. Layout of Data: two dimensional array of Doppler Frequency Groups, where a) 1st dimension is Number Of Coarse Frequency Steps or Number of Fixed Frequency repeats b) 2nd dimension is Number Of Fine Frequency Steps D. Ionogram Data Structure We have this Data Structure after Ionogram Calculation process. The following is true for this structure. 1. Group is Ionogram Frequency Group 2. Layout inside of Ionogram Frequency Group: two-dimensional array of Ionogram Databins, where A5-17 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL a) 1st dimension is Number Of Polarizations b) 2nd dimension is Number of Heights to Sample 3. Layout of Data: two dimensional array of Ionogram Frequency Groups, where c) 1st dimension is Number of Coarse Frequency Steps d) 2nd dimension is Number of Fine Frequency Steps Table 5A-5-27: Raw Databin, length 4 Byte Byte Mnemonic Offset Len Description Units 0 2 RE Real part of quadrature, from 0 to 65535 - 2 2 IM Imaginary part of quadrature, from 0 to 65535 - Type INT16U INT16U Range 0... 65535 0 ...65535 Table 5A-5-28: Doppler Databin format, length 4 Byte Byte Mnemonic Offset Len Description Units Type 0 2 AMP Amplitude, in linear scale, from 0 to 65535 - INT16U 2 2 PH Phase, from 0 to 360, but not including 360 360/65536 deg INT16U Range 0... 65535 0 ...65535 Table 5A-5-29: Ionogram Databin format 1, without PGH, length 17 Byte Byte Mnemonic Offset Len Description Units Type 0 1 DOPPLER Sequential number of Doppler 1 2 AMP1 1st antenna amplitude, linear scale, from 0 to 65535 3 2 PH1 1st antenna phase, from 0 to 360, but not including 360 5 2 AMP2 2nd antenna amplitude, linear scale, from 0 to 65535 7 2 PH2 2nd antenna phase, from 0 to 360, but not including 360 9 2 AMP3 3rd antenna amplitude, linear scale, from 0 to 65535 11 2 PH3 3rd antenna phase, from 0 to 360, but not including 360 13 2 AMP4 4th antenna amplitude, linear scale, from 0 to 65535 15 2 PH4 4th antenna phase, from 0 to 360, but not including 360 360/65536 deg 360/65536 deg 360/65536 deg 360/65536 deg INT8U INT16U INT16U INT16U INT16U INT16U INT16U INT16U INT16U Range 0…255 0... 65535 0 ...65535 0... 65535 0 ...65535 0... 65535 0 ...65535 0... 65535 0 ...65535 Table 5A-5-30: Ionogram Databin format 2, with PGH, length 19 Byte Byte Mnemonic Offset Len Description Units Type 0 1 DOPPLER Sequential number of Doppler 1 2 AMP1 1st antenna amplitude, linear scale, from 0 to 65535 3 2 PH1 1st antenna phase, from 0 to 360, but not including 360 5 2 AMP2 2nd antenna amplitude, linear scale, from 0 to 65535 7 2 PH2 2nd antenna phase, from 0 to 360, but not including 360 9 2 AMP3 3rd antenna amplitude, linear scale, from 0 to 65535 11 2 PH3 3rd antenna phase, from 0 to 360, but not including 360 13 2 AMP4 4th antenna amplitude, linear scale, from 0 to 65535 15 2 PH4 4th antenna phase, from 0 to 360, but not including 360 360/65536 deg 360/65536 deg 360/65536 deg 360/65536 deg INT8U INT16U INT16U INT16U INT16U INT16U INT16U INT16U INT16U 17 2 PH_DIFF Phase difference between this and next close frequency. This 360/65536 deg INT16U difference calculated for PGH mode, from 0 to 360, but not including 360 Range 0…255 0... 65535 0 ...65535 0... 65535 0 ...65535 0... 65535 0 ...65535 0... 65535 0 ...65535 0 …65535 Table 5A-5-31: Ionogram Databin format 3, length 4 Byte Byte Mnemonic Offset Len Description Units 0 1 SDN Sequential number of 7Strongest Doppler - Type INT8U Range 0 … 255 7 Strongest doppler is the doppler that has maximum averaged value over antennas amplitude A5-18 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 1 1 AMP Amplitude of strongest Doppler that averaged over antennas, dB INT8U given in dB scale 2 1 ZENITH Zenith of source that corresponds to strongest Doppler, 0 to 90 0.35Deg = INT8U Degrees 90 / 255 3 1 AZIMUTH Azimuth of source that corresponds to strongest Doppler, given 1.412Deg = INT8S as east deviation from geographic north direction, from 0 to 360 / 255 360 Degrees in east/clockwise direction. 0 … 255 0 … 255 -128 … 127 HOUSEKEEPING PACKETS I’m alive packet TYPE=0x01, Length = 38. DESC send this packet to DCART every minute if no science data are being produced. Byte Byte Offset Len 0 39 Mnemonic HK_HEADER Table 5A-5-32: “I’m alive“ packet structure Description Units Type Housekeeping Header - Table 5A-5-20 Range N/A Event Message packet TYPE=0x02, Length is variable but not less than 41 DESC sends this packet to report a detected software condition. Byte Byte Len Offset 0 39 39 2 41 1 42 2 * ITEM_COUNT Table 5A-5-33: Event Message packet structure Mnemonic Description Units HK_HEADER Housekeeping Header - MESSAGE_ID Message Ident - ITEM_COUNT Number of auxiliary information items - AUX_INFO Auxiliary information items - Type Table 5A-5-20 INT16U INT8U INT16U array Range N/A Table A-1 0…9 Error message packet TYPE=0x03, Length is variable but not less than 41 DESC sends this packet to report a detected software error. Byte Offset 0 39 41 42 Byte Len 39 2 1 2 * ITEM_COUNT Table 5A-5-34: Error Message packet structure Mnemonic Description Units HK_HEADER Housekeeping Header - ERROR_ID Error Ident - ITEM_COUNT Number of auxiliary information items - ERROR_INFO Auxiliary information items - Type Table 5A-5-20 INT16U INT8U INT16U array Range N/A Table A-2 0…9 PROGSCHD Countdown packet TYPE=0x04, Length = 45 bytes DESC sends this packet to report upcoming start of a scheduled program or time left for the current running schedule. Byte Byte Len Offset 0 39 Table 5A-5-35: PROGSCHD Countdown packet structure Mnemonic Description Units Type HK_HEADER Housekeeping Header - Table 5A-5-20 Range N/A A5-19 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 39 1 40 1 41 4 SCHD_NUM PROG_NUM TIME_LEFT Current Schedule Number - Upcoming Program Number - 0 = use to report time till the end of the current schedule Time left until the event sec INT8U INT8U INT32U 1-255 0, 1-255 0..4G BIT packet TYPE=0x05, Payload length =179 bytes DESC sends the BIT housekeeping packets to report hardware sensor readings. The analysis of sensor readings for yellow/red high/low tolerance limits is responsibility of the DCART software. Table 5A-5-36: Hardware Sensors payload structure Byte Byte Offset Len Mnemonic Description Uni ts Type 0 39 HK_HEADER Housekeeping header - Table 5A-5-20 39 1 SCH_NUMBER Schedule Number (0 means manual start of sounding) - INT8U 40 1 PROG_NUMBER Program Number - INT8U 41 LEN PROG BIT Program Specification (see Table 5A-5-105) -- 41+LEN 20 STATIC SENSORS Static sensor data collected in digital and analog channels Table 5A-5-37 61+LEN 16 CASE0 Sensor data collected in Case #0 of BIT - Table 5A-5-38 77+LEN 16 CASE1 Sensor data collected in Case #1 of BIT - Table 5A-5-38 93+LEN 16 CASE2 Sensor data collected in Case #2 of BIT - Table 5A-5-38 109+LEN 16 CASE3 Sensor data collected in Case #3 of BIT - Table 5A-5-38 Range 0…255 1…255 - - Byte Offset 0 4 Byte Offset 0 Bit # 0 Table 5A-5-37: Static sensor data collected in BIT Byte Mnemonic Len Description Units Type Range 4 DIGITAL Status of 32 digital sensors A, B, C, and D (Table - 4 x INT8U n/a 5A-5-39 and Error! Reference source not found.) 16 ANALOG Status of static analog sensors (Table 5A-5-40) - For each sensor, the maximum sensor value over a set of 8 x INT16U 0..1023 (10 bit ADC) collected samples is obtained by DESC to report here Table 5A-5-38: Dynamic sensor data collected in BIT case 0, 1, 2, and 3 Byte Mnemonic Len Description Units Type Range 16 ANALOG Status of 8 dynamic analog sensors (Table - 8 x INT16U - 5A-5-41) For each sensor, the maximum sensor value over a set of collected samples is obtained by DESC to report here Table 5A-5-39. Digital Sensors Mnemonic on schematics DCART Mnemonic Description Go condition O/X PWR_PREAMP_V Preamp power 0 1 -15V PWR_M15_V -15 Volt power 0 2 -5V PWR_M5_V -5 Volt power 0 3 +3.3V PWR_P3.3_V +3.3 Volt power 1 4 +15V PWR_P15_V +15 Volt power 1 5 +12V PWR_P12_V +12 Volt power 1 6 OverTemp PWR_OVER_TP Power card overheating condition 1 7 HW Test Pat PREP_HW_TESTPAT Preprocessor HW test pattern 1 A5-20 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 8 Tx_Card_Tim TX_CARD_TIMEOUTS Tx Card Commanding Timeouts since last BIT program 0 eouts 9 +18V PWR_P18_V +18 Volt power 1 10 Cmd_Timeout CMD_TIMEOUTS Commanding Timeouts since last BIT program 0 s 11 RF_Noise_Lo RF_NOISE_LOW_V w_V Environment RF noise Voltage in Antena with 0 dB gain in 0 antenna switch measured at the Tracker #4 input 12 RF_Noise_Hig RF_NOISE _HIGH_V Environment RF noise Voltage in Antena with 9 dB gain in 0 h_V antenna switch measured at the Tracker #4 input 13 Rx_Card_Tim RX_CARD_TIMEOUTS Rx Card Commanding Timeouts since last BIT program 0 eouts 14 TRACKER1_ TRACKER1_CARD_TI TRACKER1 Card Commanding Timeouts since last BIT 0 Card_Timeout MEOUTS program s 15 TRACKER2_ TRACKER2_CARD_TI TRACKER2 Card Commanding Timeouts since last BIT 0 Card_Timeout MEOUTS program s 16 TRACKER3_ TRACKER3_CARD_TI TRACKER3 Card Commanding Timeouts since last BIT 0 Card_Timeout MEOUTS program s 17 TRACKER4_ TRACKER4_CARD_TI TRACKER4 Card Commanding Timeouts since last BIT 0 Card_Timeout MEOUTS program s 18 BIT_Card_Ti BIT_CARD_TIMEOUTS BIT Card Commanding Timeouts since last BIT program 0 meouts 19 20 21 22 23 Table 5A-5-40. Analog Static Sensors Word # Mnemonic on schematics DCART Mnemonic Description 0 TEMP_SENSE AMP_TP Temperature sensor in amplifier chassis 1 PDT PWR_TP Temperature sensor on power card 2 - - - 3 - - - 4 RPD TIM_DATACLK_FR Upconverter Data I&Q Clock frequency 5 CP/PE TIM_PARPORT_FR Parallel port timing clock 6 - - - 7 - - - Range 0..1023 0..1023 0..1023 0..1023 - Word # Mnemonic on schematics 0 RF1 1 RF2 2 TX1 3 TX2 4 - 5 - 6 - 7 - Table 5A-5-41. Analog Dynamic Sensors DCART Mnemonic Description AMP_RF1_V AMP_RF2_V TX_OUT1_V TX_OUT2_V RX_MAX1 RX_MAX2 RX_MAX3 RX_MAX4 RF voltage amplitude at the output of amplifier 1 -1 if R pulse is missing RF voltage amplitude at the output of amplifier 2 -1 if R pulse is missing Output voltage at transmitter card, channel 1 -1 if R pulse is missing Output voltage at transmitter card, channel 2 -1 if R pulse is missing Maximum amplitude value in the receiver channel 1 65535 if R pulse is missing Maximum amplitude value in the receiver channel 2 65535 if R pulse is missing Maximum amplitude value in the receiver channel 3 65535 if R pulse is missing Maximum amplitude value in the receiver channel 4 65535 if R pulse is missing Range 0..1023 0..1023 0..1023 0..1023 0..46340 0..46340 0..46340 0..46340 A5-21 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Trackers Calibration data packet TYPE=0x06, Payload length is variable DESC sends the Tracker Calibration packet as a result of running of Trackers Calibration program. This packet, which contains information needed to tune hardware to any particular frequency, will be permanently saved by DCART and will be transferred to DESC each time upon the connection. Table 5A-5-42: Tracker Calibration payload structure Byte Offset 0 39 40 41 LEN Byte Len 39 1 1 P_LEN V_LEN Mnemonic HK_HEADER Description Housekeeping header Units - SCH_NUMBER Schedule Number (0 means manual start of sounding) - PROG_NUMB Program Number - ER PROG Trackers Calibration Program Specification (see Table - 5A-5-107 to 3-39) VOLT Voltages. - Each voltage occupies one byte and corresponds to its tuning frequency in the Trackers Band List described in PROG structure Type Table 5A-5-20 INT8U INT8U Range - 0…255 1…255 - - Array of INT8U TELEMETRY PACKET SUMMARY Packet ID 0x81 Packet Mnemonic SCI_DATA 0x01 HK_ALIVE 0x02 HK_EVENT 0x03 HK_ERROR 0x04 HK_CNTDOWN 0x05 HK_BIT Science Data Packet Title I Am Alive Event Message Error Message PROGSCHD Countdown Hardware Sensors Report ERROR/EVENT ID AND AUXILIARY INFORMATION Table 5A-5-43: Error Message ID and Auxiliary Information Error ID 0001h 0002h Message Text Command stream out of sync, skipped %d bytes to next sync pattern Bad checksum in packet 0x%02X Item Count 1 1 Information Number of skipped bytes until next sync pattern Command ID 0003h 0004h Command packet is %d byte long, too large for packet pool 1 Unknown Command 0x%02X 1 Byte Count Command ID A5-22 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE 0005h 0006h 0007h 0008h 0009h 000Ah 000Bh Wrong packet length of %d bytes for command 0x%02X 2 Not in Standby state for upload command 0x%02X to pro- 1 ceed Upload packet 0x%02X with grouping flag 0x%02X and 3 sequence count %d is out of sequence Incomplete upload sequence of %d packets is descarded 1 Upload data not available to execute command 0x%02X 1 System in Standby state, cannot run command 0x%02X 1 System in Standby state, cannot start schedule %d at SST 8 %4d.%02d.%02d %02d:%02d:%d.03%d 000Ch 000Eh 0011h 0012h 2101h 2201h 2202h 3101h Command 0x%02X: bad EEPROM bank number %d 2 Cannot execute command 0x%02X, command queue is full 1 Unstable clock, time drift is %d sec 1 or, if information parameter value is 0, Can not set time, check transmitter card Bad timing while running program %d, processed %d looks 2 Bad program number %d in PROG_UPLOAD command 1 Bad schedule number %d in SCHD_UPLOAD command 1 Bad program number %d in schedule %d definition 2 Cannot add schedule %d at %4d.%02d.%02d 8 %02d:%02d:%d.03%d: Bad timestamp in SST 3102h Cannot add start of schedule %d at %4d.%02d.%02d 8 %02d:%02d:%d.03%d: SST queue is full 3701h Schedule %d is empty, cannot SCHD_RUN 1 3A01h Program %d is empty, cannot PROG_RUN 1 DIGISONDE 4D SYSTEM MANUAL Command ID Byte Count Command ID Command ID Grouping Flag Sequence Count # of accepted packets Command ID Command ID Schedule # Year Month Day Hour Minute Second Millisecond CommandID Bank # CommandID Time drift in sec 0 is a special value that means time can not be set due to malfunction of transmitter card Program # Processed # of looks Program # Schedule # Program # Schedule # Schedule # Year Month Day Hour Minute Second Millisecond Schedule # Year Month Day Hour Minute Second Millisecond Schedule # Program # A5-23 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 8401h Nothing to run in Scheduled Operations state: SST Queue is 0 - empty Message ID 0007h Table 5A-5-44: Event Message ID and Auxiliary Information Message Text Program %d has been terminated Item Count 1 Program # Information 0008h Schedule %d has been terminated 1 Schedule # 0009h System clock time corrected by %d ms 1 1086h 1006h Command Half-Octave Filter Switch Frequencies Table ac- 0 knowledged Command Trackers Calibration Data acknowledged 0 Time correction in ms -1 if the value is outside the representation limits - - 1030h Commanding Bus acknowledged 0 - 1032h Command SST_FLUSH acknowledged 0 - 1033h Auto-drift message acknowledged 0 - 1071h 1072h 1073h Command PROG_UPLOAD acknowledged, new program 1 %d is accepted Command PROG_START acknowledged, starting program 1 %d Command STOP acknowledged 0 Program # Program # - 1074h 1075h 1076h Command SCHD_UPLOAD acknowledged, new schedule 1 %d is accepted Command SCHD_START acknowledged, starting schedule 1 %d Command ADD_SST acknowledged, adding schedule %d at 8 %4d.%02d.%02d %02d:%02d:%d.03%d (TBR) 1077h 1078h Command RFIL_UPLOAD acknowledged, new RFIL ver- 1 sion is %d Command RFIL_FLUSH acknowledged 0 Schedule # Schedule # Schedule # Year Month Day Hour Minute Second Millisecond RFIL version - 1081h Command STATE_STANDBY acknowledged 0 - 1082h Command STATE_DIAG acknowledged 0 - 1084h Command STATE_OPER acknowledged 0 - 1085h Command Global Parameters acknowledged 0 - A5-24 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL ANNEX B DCART TO DESC INTEFACE CONTROL DOCUMENT COMMAND PACKETS DCART send these packets to DESC. Periodic Message packet TYPE=0x70, Length = 17. The packet is used to set time on the DESC computer. Byte Offset 0 Byte Len Time LEN Mnemonic TS Description Time Stamp (see Table 5A-5-17: ) Units - Type Range Switch to Standby state packet TYPE=0x81, Length = 0. The packet is used to set DESC in Standby state. Switch to Diagnostic state packet TYPE=0x82, Length = 0. The packet is used to set DESC in Diagnostic state. Switch to Scheduled Operations state packet TYPE=0x84, Length = 0. The packet is used to set DESC in Scheduled Operations state. Load program packet TYPE=0x71, Length = LEN. The packet is used by DCART to upload program to DESC that uses it to fill the appropriate program definition structure (see Table 5A-5-10 to Table 5A-5-13) Byte Byte Offset Len 0 1 1 LEN Mnemonic PRN PR Description Program Number Operation (Table 5A-5-10 to Table 5A-5-13) Units - Type INT8U PR struct Range 1..255 Start program packet TYPE=0x72, Length = 1 The packet is used to start program. DESC should stop current program and start new program immediately. A5-25 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Byte Byte Offset Len 0 1 Mnemonic PRN Program Number Description Units - Type INT8U Range 1..255 Stop currently running program packet TYPE=0x73, Length = 0. The packet is used to stop any currently running program. Load schedule packet TYPE=0x74, Length is variable The packet is used to load schedule to the schedule structure (Table 3-3) Byte Byte Offset Len 0 1 1 LEN Mnemonic SCHN SCH Description Schedule Number Schedule (Table 5A-5-18: ) Units - Type INT8U SCH struct Range 1..255 Start schedule packet TYPE=0x75, Length = 1 The packet is used to start schedule. DESC should stop current schedule and current program and start new schedule immediately. Byte Byte Offset Len 0 1 Mnemonic SCH_N Schedule Number Description Units - Type INT8U Range 1..255 Load Start Schedule Time (SST) packet TYPE=0x76, Length = 18 The packet is used to start schedule at certain time. At that time DESC should stop current schedule and current program and start new schedule. Byte Byte Offset Len 0 1 1 17 Mnemonic SCH_N TS Description Schedule Number Time stamp (Table 5A-5-17: ) Units - Type INT8U TS struct Range 1..255 Flush Start Schedule Time (SST) Queue packet TYPE=0x32, Length = 0 The packet is used as a request to flush SST queue in DESC memory. Load Restricted Frequency Interval List packet TYPE=0x77, Length is variable The packet is used to set list of restricted frequencies. DESC should not transmit on these frequencies but still collects and reports data. Byte Offset 0 Byte Len RFIL LEN Mnemonic RFIL Description Units Restricted Frequency Interval List (Table 5A-5-21) - Type RFIL struct Range Clean Restricted Frequency Interval List packet TYPE=0x78, Length = 0 A5-26 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL The packet is used to clean list of restricted frequencies. Reboot TYPE=0x79, Length = 0. The packet is used to reboot Control computer. Auto-drift Message packet TYPE=0x33, Length = 25. The packet is used to set new recommended frequency in the auto-drift programs on the DESC computer. Two frequencies are available in the packet, FR1 for F layer, and FR2 for E layer drift. The appropriate frequency is selected by comparing height parameters HR1 and HR2 that accompany frequencies FR1 and FR2 with the bottom-top settings on the auto-drift programs. If the height parameter is within the bottom-top range of the sounding operation and time is not more than 1.5 hour from current time than DESC replaces the nominal fixed frequency value in the program specification with the new recommended value from the packet. DESC attempts to set FR1 using H1 and after that FR2 using H2. Heights are given in the units compatible with bottom-top range fields of the sounding operation. Byte Offset 0 17 Byte Len Time LEN 2 19 2 21 2 23 2 Mnemonic TS H_F-LAYER FR_F-LAYER H_E-LAYER FR_E-LAYER Description Time Stamp (see Table 5A-5-17: ) Height range one (F layer, range 80 is 100 km) Recommended frequency for drift measurements at HR1 0 = no recommendation available Height range two (E layer, range 160 is 200 km) Recommended frequency for drift measurements at HR2 0 = no recommendation available Units - Type 1.25 km INT16U kHz INT16U 1.25 km INT16U kHz INT16U Range 0 km – 2000 km 0, 1 kHz – 30000 kHz 0 km – 2000 km 0, 1 kHz – 30000 kHz Global Parameters packet TYPE=0x85, Length = 3. The packet is used to set global parameters on the DESC computer. Packed must be send at DCART-DESC reconnect, and at Global Parameters change. Byte Byte Offset Len 0 1 1 1 2 1 Mnemonic DELAY_0_KM DELAY_80_K M ENABLE_TR_ BAND Description Units Type Delay for 0 km (from beginning of R-Pulse) depends on receiver script. Delay for 80 km (from beginning of R-Pulse) depends on receiver script. Enable tracker band switching 1 = enable, normal operational mode (always 1 in operational state) 0 = disable, only for band’s width and shape testing 1.25 km 1.25 km boolean INT8U INT8U INT8U Range 0..255 0..255 0, 1 A5-27 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE 3 4 CRISTAL_CO 2 x (COMMAND BYTE, DATA BYTE) - NTROL This data are sending to DAC to provide correction of voltage to digisonde general clock Oven Controlled 61.44 MHz Oscillator. This is DCART Global parameter. It need to be tuned for every particular digisonde. Controlling address for DESC to command is 0x2C. It is two possible ways to command: First - command byte 0x01, data XX Second - command byte 24, data XX or First - command byte 0x05, data XX Second - command byte 20, data XX DIGISONDE 4D SYSTEM MANUAL 4 x INT8U - Trackers Calibration Data packet TYPE=0x06, Payload length is variable DCART sends the Load Tracker Calibration Data packet at the time of the connection. This packet contains information needed for tuning hardware to any particular frequency. Byte Offset 0 Byte Len 39 Mnemonic HK_HEADER Description Housekeeping header 39 1 SCH_NUMBER Schedule Number (0 means manual start of sounding) 40 1 PROG_NUMB Program Number ER 41 P_LEN PROG Trackers Calibration Program Specification (see Table 5A-5-107 to 3-39) LEN V_LEN VOLT Voltages. Each voltage occupies one byte and corresponds to its tuning frequency in the Trackers Band List described in PROG structure Units - - Type Table 5A-5-20 INT8U INT8U - - - Array of INT8U Range - 0…255 1…255 - This is exactly the same structure as for Payload Trackers Calibration which is created by DESC as the result of running Tarckers Calibration program. Amplifier Half-Octave Filter Switch Frequencies Table TYPE=0x86, Payload length is variable DCART sends the Amplifier Half-Octave Filter Switch Frequencies Table at the time of the connection. This packet contains information needed to switch amplifier to the correct filter band for any particular frequency. Byte Offset 0 1 Byte Len 1 SIZE * 2 Mnemonic SIZE FREQ Description Size – number of switch Frequencies List of Switch Frequencies Units kHz Type INT8U INT16U Range 1…7 0, 1 kHz – 30000 kHz Current Amplifier has seven switch frequencies. Typical example from StationSpecific.UDD: *936 < 1690 2450 4100 5550 10950 16150 22100 > A5-28 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE COMMAND LIST SUMMARY Command ID Command Mnemonic 0x70 PM 0x71 PROG_UPLOAD 0x72 PROG_START 0x73 STOP 0x74 SCHD_UPLOAD 0x75 SCHD_START 0x76 SST_UPLOAD 0x32 SST_FLUSH 0x77 RFIL_UPLOAD 0x78 RFIL_FLUSH 0x79 SYS_REBOOT 0x81 STATE_STANDBY 0x82 STATE_DIAG 0x84 STATE_OPER Command Title Periodic Message Upload program definition Start program Stop currently running program Upload schedule definition Start schedule Upload new SST Flush SST table Upload new RFIL table Clear RFIL table Reboot control computer Switch to standby state Switch to diagnostics state Switch to scheduled operations state DIGISONDE 4D SYSTEM MANUAL A5-29 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL ANNEX C DCART INTEFACE CONTROL DOCUMENT FOR DATA PRODUCTS RAW SCIENCE DATA MEASUREMENT FORMAT General considerations Science Data are arranged in Measurements. From the general point of view, Measurement characterized by Location, Time, Program, and Applied Processes List and contains some scientific data that was taken at these location and time by implementing this Program and then have been processed further by applying all the processes in the Applied Processes List. Each Measurement data are produced by running some Program that sends, using transmitter, a series of “Pulses” with specified interval between them. After any Pulse transmitted and before next Pulse, Program samples incoming signal from 256 and up to 1024 times (it depends on Program) producing Raw Science Data. Say, Raw Science Data are Science Data without any process applied to them. So we can see that Raw Science Data grouped by Pulses. We prefer to name it Looks as sometimes we do not transmit signal (Pulse) but just listening to. Further Raw Sciences Data will be underwent several known processes. Here they are in the sequence of applying: 1. Channel equalizing, mandatory. No data reduction. 2. Interference mitigation, recommended but may be omitted. No data reduction. 3. Pulse compression if applicable. No data reduction. 4. Sum complementary codes if applicable. Data are reduced by two times. 5. Regrouping by frequencies and calculation of Dopplers. No data reduction. At this point processing split into two branches depending of Program purpose that can be either to get Ionogram, “snapshot” of ionosphere/plasmasphere taken over the large number of frequencies with pretty coarse Doppler resolution, so we can observe “consistent picture of ionosphere/plasmasphere” using this data, or Drift Data, “movie” of ionosphere/plasmasphere taken over couple of selected frequencies with high Doppler Resolution. So we have two branches of processing after step 5, for Ionogram and for Drift Data. For Ionogram Data: 6. Choosing the strongest (having maximum amplitude over all antennas) Doppler for each height. 7. Calculating angle of arrival for strongest Doppler. A5-30 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 8. For each height (for both ordinary and extraordinary data), leaving only, Doppler value itself, average amplitude over antennas of strongest Doppler, and angles of arrival. For Drift Data: 6. Reducing Drift Data by excluding weak Dopplers, i.e. Dopplers that have “average over antennas” amplitude less than most probable amplitude (for Dopplers of the same frequency and height) plus sum threshold. The others, strong Dopplers, are also called Sources of Reflection or just Sources. DDAS.EXE program does this. 7. Calculating angles of arriving for all Sources, reducing data further, approximately 4 times for 4 antennas. Presently it can be done only by DDAS.EXE. Produced data is called Skymap Data. 8. Calculating of bulk velocity using statistical behavior of Sources. Presently it can be done only by DDAV.EXE. Produced data is called Velocity Data. Let’s put aside Skymap and Velocity Data as they differ from others. Then we see that Science Data are grouped either by Look or by Frequency so we can say about Look or Frequency Groups, where each Look/Frequency Group has one Look/Frequency Header (containing information unique to the look/frequency) and, predicted out of Program and Applied Processes List, constant number of Databins collected on the look or frequency. Also it is clear that Science Data are grouped by Looks up to step 5 and grouped by Frequency after step 5. We will use the following structures: Measurement, Measurement Signature, Measurement Header, Measurement General Header, Preface, Look Group, Frequency Group, Look Header, Frequency Header and also auxiliary structures as Antenna Configuration, Antenna Coordinates Array, Coordinates. Measurement consists of:  Measurement Header  Look or Frequency Groups, repeated as many times as describes in Preface Measurement Header consists of:  Measurement Signature  Generic Format Measurement Version  Measurement General Header  Preface Byte Offset 0 6 7 7+ MGH_len Byte Len 6 1 MGH_len P_len Table 5C-5-45: Measurement Header, length is variable Mnemonic Description Units Type SIGNATURE Measurement Signature contains six bytes fixed data N/A INT8U array 0xFE, 0xFA, 0x31, ‘D’, ‘P’, ‘S’ Each Measurement starts from these bytes. GFM_VER Generic Format Measurement Version. N/A INT16U MGHDR Measurement General Header - N/A PREF Preface - N/A Range N/A 0 … 254 N/A N/A A5-31 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Byte Offset Byte Len 0 4 4 1 5 1 6 1 Table 5C-5-46: Measurement General Header, length 7 bytes Mnemonic Description Units Type M_LEN Length of Measurement, in bytes. Signature is included. - Value 0 means abnormal stop of measurement creating process and so this measurement has to be considered as damaged and not to be underwent further normal consid- eration. M_COMPL Completeness. % It is calculated as ratio of length of measurement taken from field LENGTH to complete length of measurement. So the maximum possible value 100 means measurement is completed and any other value means some incomplete- ness. The less value – the more incompleteness. M_TRUNC This field can keep only two values: - 0 – measurement is not truncated, means tail of measurement is present. 1 – measurement is truncated, means tail of meas- urement is lost. M_N_GAPS Number of gaps in measurement data. - For completed measurement this value is always 0. Value 255 means 255 or more gaps. INT16U INT8U INT8U INT8U Range 0 … 4Gb 0 … 100 0 or 1 0 … 255 Byte Byte Offset Len 0 2 2 17 19 4 23 2 25 2 27 32 52 52 + A_len 60 + A_len 61 + A_len 62 + A_len 64 + A_len 65 + A_len 66 + A_len 68 + A_len 69 + A_len 70 + A_len 5 20 A_len 8 1 1 2 1 1 2 1 1 1 Table 5C-5-47: Measurement Preface Specification, length is variable Mnemonic Description Units Type Range SID TIME_STAMP M_RUNTIME Station Identification Number Time Stamp of start time (Table 3-2) Real length of measurement LAT LON URSI STN ANT_CONF EQUIP Latitude, from -90 deg to 90 deg Eastern Longitude, from 0 to 360 deg URSI code given in ASCII characters Station name given in ASCII characters Antennas configuration Equipment, given as ASCII characters ms Hundredth of Degrees Hundredth of Degrees - INT16U TS INT32U INT16S INT16U 0 … 65535 0 to 4Gb Up to 50 days, approx. -9000 to 9000 0 to 36000 ASCII bytes N/A ASCII bytes N/A ACONF N/A ASCII bytes N/A DESC_MAJ_VER DESC Major Version - Informative field DESC_MIN_VER DESC Minor Version - Informative field DESC_BLD_NUM DESC Build Number - Informative field DCART_MAJ_VER DCART Major Version - Informative field DCART_MIN_VER DCART Minor Version - Informative field DCART_BLD_NUM DCART Build Number - Informative field SCH_NUM Schedule Number (0 means manual start of sound- - ing) PROG_NUM Program Number - INT8U INT8U INT8U INT8U INT8U INT8U INT8U INT8U 0 … 255 0 … 255 0 … 65535 0 … 255 0 … 255 0 … 65535 0…255 1…255 NAPS Number of Applied Process Steps A5-32 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 71 + NAPS APS A_len 71 + 1 A_len + NAPS NP_DESC 72 + A_len + NAPS P_len PROG Applied Process Steps. Each Process Steps occu- pies one byte and contain Process Step Code as following: 1 – RFIM 2 – Pulse Compression 3 – Sum Complementary Codes 4 – Doppler Calculation 5 – Ionogram Producing Number of Processes that have been done by DESC. If 0 then all processes have been done by DCART, otherwise it indicates number of first processes in APS that have been done by DESC. Program Specification (see Tables 3-1-x) - Array of N/A Process Codes INT8U 0 … 255 - - Table 5C-5-48: Antennas configuration, length is variable, e.g. 58 (for 4 antennas) Byte Byte Len Off- Mnemonic Description Units Type Range set 0 1 ANT_NUM Number of antennas - INT8U 4 1 1 ANT_LOUT Antenna Layout: 0 - non-standard layout 3 - four-antenna standard - INT8U 0, 3, 4 4 - four-antenna mirrored 2 2 ANT_DEVN Antenna Deviation: Deviation, in of degrees, of direction 3-1 from compass north. Values are from -180 to 180. Positive means counter-clockwise. It is used only for standard layouts Hundredth of Degrees INT16S -18000 .. 18000 ( from -180 deg to 180 deg) 4 4 ANT_MAXD Antenna Max Distance: The max distance between antennas in meters. It is used only for standard layouts. As all standard layouts assumed equilateral triangles then MAXDIST for 4-antennas standard layout is equal to the length of triangle side. Centimeter INT32U 1… 4294967295 (from 1 cm to approx. 42K km) 8 2 X_AXIS_DECL DECLINATION (angle) OF X-AXIS from Geographic Pole. Values from 0 to 180 degrees mean clockwise declination and values from 0 to -180 degrees mean anti-clockwise declination Hundredth of Degrees INT16S -18000 .. 18000 ( from -180 deg to 180 deg) 10 12 x ANT_COOR Array of Coordinates structure (Table 4-1-1) - COOR N/A ANT_NUM array Antennas coordinates array, number of elements = number of antennas This is an array of Coordinates structures, 1st element is the first antenna coordinates and so on. The following is true. a) Antenna 1 at (0, 0, 0) b) X-axis is pointing ground level compass North c) Y-axis is pointing ground level compass West Table 5C-5-49: Coordinates configuration, length 12 Byte Byte Offset Len Mnemon- Description Units Type Range ics A5-33 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 0 4 X X-coordinate in centimeters 4 4 Y Y-coordinate in centimeters 8 4 Z Z-coordinate in centimeters Centimeter Centimeter Centimeter INT32S INT32S INT32S -2147483648 to 2147483647 (from -21K km to 21K km, approx.) -2147483648 to 2147483647 (from -21K km to 21K km, approx.) -2147483648 to 2147483647 (from -21K km to 21K km, approx.) Table 5C-5-50: Look Header, length 22 Byte Byte Mnemonic Offset Len Description Units 0 4 LN Look Number, sequential number starting from 0 - 4 4 PSO Time Offset of Look from measurement start time (ST) Ms 8 2 F_OFF Offset of applied frequency from nominal frequency. kHz Nominal frequency calculated using Look Number and Frequency Stepping Law (from Program structure) 10 1 RFF Restricted Frequency Flag ( 0 – not restricted, 1 – re- - stricted) 11 8 S_F Scale Factor. When data are saved into external storage - they are checked against overflowing and if it is occurred than all data in this look divide on this calculated Scale Factor. Upon restoring from you need multiply data on Scale Factor. Type INT16U INT32U INT16S Range 1 .. 4Gb 0 to 4294967296 ms or approx. 50 days -32768 … 32767 INT8U 0, 1 Double that follows specification IEEE754 As any non-negative double value in Java 19 1 AS 20 2 SAT Attenuation Selection Notes: 1. Positive value means attenuation was applied by DESC whereas negative value means gain was applied by DESC. 2. Attenuation selection does not include Constant Gain (from Program) Saturation flag (used only for digital transceiver) (TBR) 0 – no saturation but need more gain 1 – no saturation, perfect gain 3 – saturated, need less gain dB where, dB(a)= 20log10(a) - INT8S - -128 … 127 0, 1, 3 (TBR) Table 5C-5-51: Frequency Header, length 22 Byte Byte Mnemonic Offset Len Description Units 0 4 FRN Frequency Number, sequential number starting from 0 - 4 4 FSO Time Offset of Frequency sounding from measurement Ms start time (ST) 8 2 F_OFF Offset of applied frequency from nominal frequency. kHz Nominal frequency calculated using Look Number and Frequency Stepping Law (from Program structure) 10 1 RFF Restricted Frequency Flag (0 – not restricted, 1 – restricted) - 11 8 S_F Scale Factor. When data are saved into external storage they are checked against overflowing and if it is occurred than all data in this look divide on this calculated Scale Factor. Upon restoring from you need multiply data on Scale Factor. Type INT16U INT32U INT16S Range 1 .. 4Gb 0 to 4294967296 ms or approx. 50 days -32768 … 32767 INT8U Double that follows specification IEEE754 0, 1 As any non-negative double value in Java A5-34 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 19 1 AS 20 2 SAT Attenuation Selection Notes: 1. Positive value means attenuation was applied by DESC whereas negative value means gain was applied by DESC. 2. Attenuation selection does not include Constant Gain (from Program) Saturation flag (used only for digital transceiver) (TBR) 0 – no saturation but need more gain 1 – no saturation, perfect gain 3 – saturated, need less gain dB where, dB(a)= 20log10(a) - INT8S INT8U -128 … 127 0, 1, 3 (TBR) Byte Offset 0 22 Table 5C-5-52: Height-restricted Frequency Header8, length 26 Byte Mnemonic Len Description Units Type 22 F_HEAD Frequency Header structure - - 4 S_HGT Start height/range of successively output heights/ranges, meter total number of ranges for output is equal to NRO parame- ter of measurement program structure INT32U Range 0 to 4294967296 m or ≈ 675 Re Table 5C-5-53: Look Group, length is variable but the same for all groups within the same measurement Byte Byte Mnemonic Offset Len Description Units Type Range 0 20 PHDR Look Header - N/A N/A 22 PDATA Look Data, two-dimensional array containing Look Databins - Two dimensional N/A (see tables 8-12 and 8-13) with 1st dimension equals to Number of Array of Look Antennas and second dimension equals to Number of Heights. Databins Table 5C-5-54: Doppler Frequency Group, length is variable but the same for all groups within the same measurement Byte Byte Mnemonic Offset Len Description Units Type Range 0 20 FHDR Frequency Header - N/A N/A 22 FDATA Doppler Frequency Group Data. - Four dimensional N/A Four dimensional array of Doppler Databins (see tables 8-14 and Array of Doppler 8-15): Databins NumberOfPolarizations x NumberOfRanges x NumberOfAntennas x NumberOfDopplers Table 5C-5-55: Ionogram Frequency Group, length is variable but the same for all groups within the same measurement Byte Byte Mnemonic Offset Len Description Units Type Range 0 20 FHDR Frequency Header - N/A N/A 22 FDATA Ionogram Frequency Group Data. - Two dimensional Array of N/A Two dimensional array of Ionogram Databins (see tables 8-16 to Ionogram Databins 8-25): NumberOfPolarizations x NumberOfRanges Byte Offset 0 2 Bit Offset Table 5C-5-56: Raw Databin uncompressed format (format 0), length 4 Byte Mnemonic Len Description Units Type 2 RE Real part of quadrature, from 0 to 65535 - INT16U 2 IM Imaginary part of quadrature, from 0 to 65535 - INT16U Table 5C-5-57: Raw Databin compressed format (format 1), length 2 Bits Mnemonic Len Description Units Type Range 0... 65535 0 ...65535 Range 8 It is used for Doppler data product when value of NRO is not zero A5-35 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 0 7 AMP Amplitude, in dB scale, from 0 to 96 96/127 dB INT7U 0... 127 7 9 PH Phase, from 0 to 360, but not including 360 360/512 deg INT9U 0 ...511 Table 5C-5-58: Doppler Databin uncompressed format (format 0), length 4 Byte Byte Mnemonic Offset Len Description Units Type Range 0 2 AMP Amplitude, in linear scale, from 0 to 65535 - INT16U 0... 65535 2 2 PH Phase, from 0 to 360, but not including 360 360/65536 deg INT16U 0 ...65535 Table 5C-5-59: Doppler Databin compressed format (format 1), length 2 Bit Bits Mnemonic Offset Len Description Units Type Range 0 7 AMP Amplitude, in dB scale, from 0 to 96 96/127 dB INT7U 0... 127 7 9 PH Phase, from 0 to 360, but not including 360 360/512 deg INT9U 0 ...511 Table 5C-5-60: Ionogram Databin uncompressed format (format 0), without PGH, length 17 Byte Byte Mnemonic Offset Len Description Units Type Range 0 1 DOPPLER 1 2 AMP1 1st antenna amplitude, linear scale, from 0 to 65535 3 2 PH1 1st antenna phase, from 0 to 360, but not including 360 5 2 AMP2 2nd antenna amplitude, linear scale, from 0 to 65535 7 2 PH2 2nd antenna phase, from 0 to 360, but not including 360 9 2 AMP3 3rd antenna amplitude, linear scale, from 0 to 65535 11 2 PH3 3rd antenna phase, from 0 to 360, but not including 360 13 2 AMP4 4th antenna amplitude, linear scale, from 0 to 65535 15 2 PH4 4th antenna phase, from 0 to 360, but not including 360 360/65536 deg 360/65536 deg 360/65536 deg 360/65536 deg INT8U INT16U INT16U INT16U INT16U INT16U INT16U INT16U INT16U 0…255 0... 65535 0 ...65535 0... 65535 0 ...65535 0... 65535 0 ...65535 0... 65535 0 ...65535 Table 5C-5-61: Ionogram Databin uncompressed format (format 0), with PGH, length 19 Byte Byte Mnemonic Offset Len Description Units Type Range 0 1 DOPPLER 1 2 AMP1 1st antenna amplitude, linear scale, from 0 to 65535 3 2 PH1 1st antenna phase, from 0 to 360, but not including 360 5 2 AMP2 2nd antenna amplitude, linear scale, from 0 to 65535 7 2 PH2 2nd antenna phase, from 0 to 360, but not including 360 9 2 AMP3 3rd antenna amplitude, linear scale, from 0 to 65535 11 2 PH3 3rd antenna phase, from 0 to 360, but not including 360 13 2 AMP4 4th antenna amplitude, linear scale, from 0 to 65535 15 2 PH4 4th antenna phase, from 0 to 360, but not including 360 360/65536 deg 360/65536 deg 360/65536 deg 360/65536 deg INT8U INT16U INT16U INT16U INT16U INT16U INT16U INT16U INT16U 0…255 0... 65535 0 ...65535 0... 65535 0 ...65535 0... 65535 0 ...65535 0... 65535 0 ...65535 17 2 PH_DIFF Phase difference between this and next close frequency. This 360/65536 deg INT16U 0 …65535 difference calculated for PGH mode, from 0 to 360, but not including 360 Table 5C-5-62: Ionogram Databin compressed format (format 1), without PGH, length 9 Bit Bit Mnemonic Offset Len Description Units Type Range 0 8 DOPPLER 8 7 AMP1 1st antenna amplitude, dB scale, from 0 to 96 15 9 PH1 1st antenna phase, from 0 to 360, but not including 360 24 7 AMP2 2nd antenna amplitude, dB scale, from 0 to 96 31 9 PH2 2nd antenna phase, from 0 to 360, but not including 360 40 7 AMP3 3rd antenna amplitude, dB scale, from 0 to 96 47 9 PH3 3rd antenna phase, from 0 to 360, but not including 360 56 7 AMP4 4th antenna amplitude, dB scale, from 0 to 96 63 9 PH4 4th antenna phase, from 0 to 360, but not including 360 96/127 dB 360/512 deg 96/127 dB 360/512 deg 96/127 dB 360/512 deg 96/127 dB 360/512 deg INT8U INT7U INT9U INT7U INT9U INT7U INT9U INT7U INT9U 0…255 0... 127 0 ...511 0... 127 0 ...511 0... 127 0 ...511 0... 127 0 ...511 Table 5C-5-63: Ionogram Databin compressed format (format 1), with PGH, length 10 Bit Bit Mnemonic Offset Len Description Units Type Range A5-36 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 0 8 DOPPLER 8 7 AMP1 1st antenna amplitude, dB scale, from 0 to 96 15 9 PH1 1st antenna phase, from 0 to 360, but not including 360 24 7 AMP2 2nd antenna amplitude, dB scale, from 0 to 96 31 9 PH2 2nd antenna phase, from 0 to 360, but not including 360 40 7 AMP3 3rd antenna amplitude, dB scale, from 0 to 96 47 9 PH3 3rd antenna phase, from 0 to 360, but not including 360 56 7 AMP4 4th antenna amplitude, dB scale, from 0 to 96 63 9 PH4 4th antenna phase, from 0 to 360, but not including 360 96/127 dB 360/512 deg 96/127 dB 360/512 deg 96/127 dB 360/512 deg 96/127 dB 360/512 deg INT8U INT7U INT9U INT7U INT9U INT7U INT9U INT7U INT9U 0…255 0... 127 0 ...511 0... 127 0 ...511 0... 127 0 ...511 0... 127 0 ...511 72 8 PH_DIFF Phase difference between this and next close frequency. This 360/256 deg difference calculated for PGH mode, from 0 to 360, but not including 360 INT8U 0 …255 Table 5C-5-64: Ionogram Databin, antennas-convolved uncompressed format (format 2) without PGH, length 7 Byte Byte Mnemonic Offset Len Description Units Type Range 0 1 DOPPLER Sequential number of strongest Doppler - INT8U 0 … 255 1 2 AMPL Amplitude, in linear scale - INT16U 0 ... 65535 3 2 ZENITH Zenith of arrival, from 0 to 90 90/65536 deg INT16U 0 …65535 5 2 AZIMUTH Azimuth of arrival, from 0 to 360, but not including 360 360/65536 deg INT16U 0 …65535 Table 5C-5-65: Ionogram Databin, antennas-convolved uncompressed format (format 2) with PGH, length 9 Byte Byte Mnemonic Offset Len Description Units Type Range 0 1 DOPPLER Sequential number of strongest Doppler - INT8U 0 … 255 1 2 AMPL Amplitude, in linear scale - INT16U 0 ... 65535 3 2 ZENITH Zenith of arrival, from 0 to 90 90/65536 deg INT16U 0 …65535 5 2 AZIMUTH Azimuth of arrival, from 0 to 360, but not including 360 360/65536 deg INT16U 0 …65535 7 2 PH_DIFF Phase difference between this and next close frequency. 360/65536 deg INT16U 0 …65535 This difference calculated for PGH mode, from 0 to 360, but not including 360 Table 5C-5-66: Ionogram Databin, antennas-convolved compressed format (format 3) without PGH, length 4 Bit Bit Mnemonic Offset Len Description Units Type Range 0 8 DOPPLER Sequential number of strongest Doppler - INT8U 0 … 255 8 7 AMPL Amplitude, in dB scale 96/127 dB INT7U 0 ... 127 15 7 ZENITH Zenith of arrival, from 0 to 90 90/127 deg INT7U 0 …127 22 10 AZIMUTH Azimuth of arrival from 0 to 360, but not including 360 360/1024 deg INT10U 0 …1023 Table 5C-5-67: Ionogram Databin, antennas-convolved compressed format (format 3) with PGH, length 5 Bit Bit Mnemonic Offset Len Description Units Type Range 0 8 DOPPLER Sequential number of strongest Doppler - INT8U 0 … 255 8 7 AMPL Amplitude, in dB scale 96/127 dB INT7U 0 ... 127 15 7 ZENITH Zenith of arrival, from 0 to 90 90/127 deg INT7U 0 …127 22 9 AZIMUTH Azimuth of arrival, from 0 to 360, but not including 360 360/512 deg INT9U 0 …511 31 9 PH_DIFF Phase difference between this and next close frequency. 360/512 deg INT9U This difference calculated for PGH mode, from 0 to 360, but not including 360 0 …511 Table 5C-5-68: Ionogram Databin, very compressed format (format 4) without PGH, length 2 Bit Bit Mnemonic Offset Len Description Units Type Range 0 3 DOPPLER Sequential number of strongest Doppler - INT3U 0 …7 3 5 AMPL Amplitude, in dB, from 0 to 93 3 dB INT5U 0 ... 31 A5-37 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 8 3 ZENITH Zenith of arrival, from 0 to 48 8 deg INT3U 0 …7 Note: value 7 signals ‘zenith/azimuth values are not calculable’ 11 5 AZIMUTH Azimuth of arrival, from 0 to 360, but not including 360 360/32 = INT5U 0 …31 11.25 deg Note: For supposedly better compression, all 1’s will be put in azimuth field when zenith/azimuth values are not calculable Table 5C-5-69: Ionogram Databin, very compressed format (format 4) with PGH, length 2 Bit Bit Mnemonic Offset Len Description Units Type Range 0 3 DOPPLER Sequential number of strongest Doppler - INT3U 0 …7 3 5 AMPL Amplitude, in dB, from 0 to 93 3 dB INT5U 0 ... 31 8 3 ZEN_AZ Zenith + Azimuth are coded as follows: 0 - vertical - INT3U 0 …7 1 - oblique, azimuth is 0 degrees 2 - oblique, azimuth is 60 degrees 3 - oblique, azimuth is 120 degrees 4 - oblique, azimuth is 180 degrees 5 - oblique, azimuth is 240 degrees 6 - oblique, azimuth is 300 degrees 7 - zenith/azimuth are not calculable 11 5 PH_DIFF Phase difference between this and next close frequency. 360/32 = INT5U 0 …31 This difference calculated for PGH mode, from 0 to 360, 11.25 deg but not including 360 A5-38 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL LEGACY SCIENCE DATA FORMATS: RSF AND SBF IONOGRAMS The header of raw data files contains General Purpose PREFACE. The format of PREFACE is outlined in Table 6-3. Refer to Section 4 (Operating Instructions) for the explanation of options and default values of operator-selectable PREFACE parameters. BYTE # 1 2,3 4 5 6 7 8 9, 10,11 12, 13,14 15 16 17, 18,19 20, 21 22, 23, 24 25, 26 27 28 29 30 31, 32 Table 5C-5-70: General Purpose PREFACE Specification DESCRIPTION UNITS RANGE TYPE Year years 0-99 packed BCD FORMAT 2 digits Day of Year days 1-366 packed BCD 4 digits Month months 1-12 packed BCD 2 digits Day of Month days 1-31 packed BCD 2 digits Hour hours 0-23 packed BCD 2 digits Minute minutes 0-59 packed BCD 2 digits Second seconds 0-59 packed BCD 2 digits Station ID: Receiver - 000-999 char 3 chars Station ID: Transmitter - 000-999 char 3 chars Schedule - 1-6 packed BCD 2 digits Program - 1-7 (A-G) packed BCD 2 digits Start Frequency, LL 100 Hz 010000 - 450000 packed BCD 6 digits Coarse Frequency Step, C 1 kHz 1-2000 packed BCD 4 digits Stop Frequency, UU 100 Hz 010000 - 450000 packed BCD 6 digits Fine Frequency Step, F 1 kHz 0 - 9999 packed BCD 4 digits Number of small steps in a scan, S -15 to +15 signed char I3 negative value means no multiplexing Phase Code, X - 1 (complim.) packed BCD 2 digits 2 (short) 3 (75% duty) 4 (100% duty) +8 (no phase switch) Multi-antenna sequencing and O/X polarization options, A 0 (sum), signed char I3 1-4 (individual anten- nas), 7 (antenna scan), +8 (only O polarization), negative for alternative antennas Number of samples for FFT, N encoded, actual # is power of 2 3-7 (power of 2) packed BCD 2 digits Pulse Repetition Rate, R pps 50, 100, 200. packed BCD 1 + 3 nibble 4: digits 0 - Active Mode 1 - Radio Silent Mode A5-39 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL BYTE # 33,34 35 DESCRIPTION Range Start, E Range Increment, H 36.37 Number of heights, M 38,39 Delay, K 40 Base Gain, G 41 Frequency Search Enabled, I 42 Operating Mode, Y 43 Data Format, D 44 Printer Output, P2 45 Threshold 46-48 Spare 49, 50 CIT Length 51 Journal 52, 53 Bottom of the height window, B 54, 55 Top of the height window, T 56, 57 Number of heights to store, O UNITS 1 km RANGE 0 - 9999 TYPE FORMAT packed BCD 4 digits encoded 2 (2.5 5 (5 10 (10 km) km) packed BCD 2 digits km) units 128, 256, 512 packed BCD 4 digits 15 km 0 - 1500 packed BCD 4 digits dB 0-7 (0-42 dB) packed BCD 2 digits +8 (+auto gain) - 0 1 (yes) (no) packed BCD 2 digits - 0 (VI) packed BCD 2 digits 1 (Drift Std) 2 (Drift Auto) 3 (Calibration) 4 (HRR) 5 (Beam) 6 (PGH) 7 (Test) - 0 (no data) packed BCD 2 digits 1 (MMM) 2 (Drift) 3 (PGH) 4 (RSF) 5 (SBF) 6 (BIT) high nibble: 0 (no Artist) 1 (with Artist) - 0 (none) packed BCD 2 digits 1 (b/w) 2 (color) 3 dB over the MPA 0 - no threshold 1 - MPA - 27 dB ... 9 - MPA - 3 dB 10 - MPA 11 - MPA + 3 dB 12 - MPA + 6 dB ... packed BCD 2 digits msec - 1 km 1 km units 0-40000 bit0: new bit1: new bit2: new bit3: new case 0-9999 0-9999 1-512 unsigned int I5 gain char Z4 height freq. packed BCD 4 digits packed BCD 4 digits packed BCD 4 digits A5-40 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL RSF Format: File Specification An RSF ionogram file consists of a variable number of 4 096 byte blocks. Each block contains a Header and a variable number of Frequency Groups. The RSF Header structure is described in the Table 5C-5-71. RSF HEADER ITEM Table 5C-5-71: The RSF Header DESCRIPTION UNITS RANGE ACCURACY PRECISION TYPE Record Type Block identifica- tion 7 (first block) exact 6 (all other blocks) exact char (1 byte) Header Length Total number of bytes taken by Header 60, fixed exact exact char (1 byte) Version Marker Version control - FF (hex), fixed - - char char (1 byte) General Purpose See Table 6-3 PREFACE FORMAT Z2 I2 Z2 Each Frequency Group contains a 6-byte PRELUDE and a single height profile of a variable length. Table 5C-5-72 summarizes the possible settings of Frequency Group lengths depending on the number of heights selected by the operator. Table 5C-5-72: Length of the RSF Frequency Groups Depending on Ionogram Settings NUMBER OF HEIGHTS PREFACE Char #36-37) NUMBER OF FREQUENCY GROUPS IN A BLOCK NUMBER OF RANGE BINS STORED IN A GROUP LENGTH OF A FREQUENCY GROUP (BYTES) 128 15 128 262 256 8 249 504 512 4 501 1008 For each sounding frequency, one or two Frequency Groups are stored depending on a setting of O/X polarization option, A, PREFACE Char #29. If A is less than 8, both polarizations are stored each taking an individual Frequency Group, otherwise only O polarization height profile is stored for each frequency. Each range bin takes 2 bytes in an RSF Frequency Group (see Table 5C-5-73 and Table 5C-5-74) Table 5C-5-73: Content of an Individual Range Bin in RSF File Format MSB LSB 5-bit Amplitude 3-bit Doppler Number Byte 1 5-bit Phase 3-bit Azimuth Byte 2 A5-41 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Table 5C-5-74: Individual Bit Sections of the Range Bin ITEM UNITS RANGE ACCURACY PRECISION TYPE FORMAT Amplitude 3 dB 0-31 1 1 5 bit unsigned integer - Doppler See text 0-7 1 1 3 bit unsigned integer - Number Phase or 11.25 or 1 0-31 1 1 5 bit unsigned integer - PGH km Azimuth 60 0-7 (0-359) 1 1 3 bit unsigned integer - The 6-byte PRELUDE precedes each set of range bins in a Frequency Group (see Table 5C-5-75). The PRELUDE uses a packed-BCD encoding scheme where each byte contains two 4-bit digits (0-9) each taking a nibble. The frequency reading stored in PRELUDE is the actual sounding frequency. The offset from the nominal frequency is stored in byte #4. If offset was caused by forcing of sounding out of restricted frequency range, the actual frequency reading is given and the offset is set to E (hex) to indicate the case. Table 5C-5-75: RSF PRELUDE Byte Organization BYTE # 1 high nibble low nibble 2, 3 4 high nibble low nibble 5 6 DESCRIPTIO N Polarization UNITS - Group size encoded Frequency Reading Offset 10 kHz encoded Additional Gain 3 dB Seconds sec Most Probable 3 dB Amplitude RANGE ACCURACY PRECISION 3 (O) 2 (X) 2 (262), 3 (504), 4 (1004) within the ionogram frequency range 0 (-20 kHz) 1 (-10 kHz) 2 (no offset) 3 (+10 kHz) 4 (+20 kHz) 5 (search failure) E (forced) F (no transmission) 0-15 10 kHz - 3 dB 10 kHz - 3 dB 00-59 1 1 0-31 3 dB 3 dB TYPE BCD nibble BCD nibble packed BCD nibble nibble packed BCD packed BCD FORMAT 1 digit 1 digit 4 digits Z1 Z1 2 digits 2 digits The last block of an RSF ionogram may be incomplete. To indicate END-OF-IONOGRAM (EOI), a 6-byte EOI marker consisting of EE(hex) is put on place of the PRELUDE. SBF Format: File Specification The SBF ionogram file consists of a variable number of 4096 byte blocks. Each block contains a Header and a variable number of Frequency Groups. The SBF Header structure is described in Table 5C-5-76. SBF HEADER ITEM Record Type Header Length Table 5C-5-76: The SBF Header DESCRIPTION block identification total number of UNITS - - RANGE 3 (first block) 2 (all other blocks) 60, fixed ACCURACY exact exact PRECISION exact exact TYPE char (1 byte) char FORMAT Z2 I2 A5-42 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL bytes taken by Header Version Marker Version control - FF (hex), fixed - - char General Purpose See Table 6-3 PREFACE (1 byte) char Z2 (1 byte) Each Frequency group contains a 6-byte PRELUDE and a single height profile of a variable length. Table 5C-5-77 summarizes the possible settings of Frequency Group lengths. Table 5C-5-77: Length of the SBF Frequency Groups Depending on Ionogram Settings NUMBER OF HEIGHTS (PREFACE Char #36- 37) NUMBER OF FREQUENCY GROUPS IN A BLOCK NUMBER OF RANGE BINS STORED IN A GROUP LENGTH OF A FREQUENCY GROUP (BYTES) 128 30 128 134 256 15 256 262 512 8 498 504 For each sounding frequency, one or two Frequency Groups are stored depending on a setting of O/X polarization option, A, PREFACE Char #29. If A is less than 8, both polarizations are stored each taking an individual Frequency Group, otherwise only an O polarization height profile is stored for each frequency. Each range bin takes 1 byte in a SBF Frequency Group (see Table 5C-5-78 and Table 5C-5-79). Table 5C-5-78: Content of an Individual Range Bin in SBF File Format MSB LSB 5-bit Amplitude 3-bit Doppler Number Byte 1 ITEM Amplitude Doppler Number Table 5C-5-79: Individual Bit Sections of the Range Bin UNITS RANGE ACCURACY PRECISION TYPE 3 dB 0-31 1 1 5 bit unsigned integer See text 0-7 1 1 3 bit unsigned integer FORMAT - - The 6-byte PRELUDE precedes each set of range bins in a Frequency Group (see Table 5C-5-80). The PRELUDE uses a packed-BCD encoding scheme, and the stored frequency reading is the actual sounding frequency. The offset from the nominal frequency is stored in byte #4. If the offset was caused by forcing of sounding out of restricted frequency range, the actual frequency reading is given and the offset is set to E (hex) to indicate the case. BYTE # Table 5C-5-80: SBF PRELUDE Organization DESCRIPTION UNITS RANGE ACCURACY PRECISION TYPE FORMAT 1 high Polarization - 3 (O) - - nibble 2 (X) BCD nibble 1 digit A5-43 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL low Group size nibble encoded 1 2 3 (504) (134), (262), 2, Frequency 10 kHz within the ionogram 10 kHz 3 Reading frequency range 4 high Offset nibble encoded 0 (-20 kHz) - 1 (-10 kHz) 2 (no offset) 3 (+10 kHz) 4 (+20 kHz) E (forced) F (no transmission) low Additional Gain 3 dB nibble 0-15 3 dB 5 Seconds sec 00-59 1 6 Most Probable 3 dB 0-31 Amplitude 3 dB 10 kHz - 3 dB 1 3 dB BCD nibble 1 digit packed BCD nibble 4 digits Z1 nibble packed BCD packed BCD Z1 2 digits 2 digits The last block of an SBF ionogram may be incomplete. To indicate END-OF-IONOGRAM (EOI), a 6-byte EOI marker consisting of EE(hex) is put on place of the PRELUDE. LEGACY SCIENCE DATA FORMATS: DFT The DFT drift data file consists of a variable number of 4 096 byte blocks, each block containing 8-bit amplitudes and phases of the Doppler spectra. The smallest data entity is a sub-case which contains a four Doppler spectrum for each antenna obtained at one frequency, one height gate, and one polarization setting. Each Doppler spectrum in a sub-case is 2N elements long, where N is selected by the operator. The amplitudes of individual Doppler spectra are grouped in sets of 128 elements for storage in the DFT file, each set of 128 amplitudes may contain data from one to four antennas depending on the setting of N. 128 amplitudes are followed by 128 phase values of the same Doppler spectrum or spectra. The first byte of the first block in the DFT file is always forced to be a Record Type 10 (Hex). The structure shown by Table 5C-5-81 on the next page illustrates the arrangement. BLOCK COUNT BYTE COUNT Table 5C-5-81: DFT File Structure DATA DESCRIPTION 1 1 Record Type 10 (hex) fixed 2-128 1st 128/2N * 8-bit amplitude spectra (as log-amplitudes in 3/8 dB units) with least significant bit replaced by serially written header data 129-256 128 8-bit Phase values of Doppler lines stored in previous 128 bytes 257-4096 Repeat previous 256 bytes 15 more times. Order of spectra is antenna 1-4, heights, frequencies, polarization 2 4096-... Repeat 4 096 byte blocks until end of data, placing 256 bytes of EE (hex) at end of data. If not end of a 4 096 byte block, then zero fill * Where 2N is # of Doppler lines in the stored spectra A5-44 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL For one frequency a variable number of height gates may be selected. All sub-cases recorded for a single frequency comprise a Height Set and all those recorded simultaneously during one CIT are called a CIT Set. All sub-cases contained within one 4 096 block of drift data comprise a Case. The drift HEADER information is stored serially in the LSB of spectra amplitude bytes, LSB of the values first. The HEADER consists of Record Type (8 bits), Header Length (16 bits), Version Indicator (8 bits), Drift PREFACE (228 bits), and a variable number of sub-case headers (52 bits each). This arrangement is illustrated in Table 5C-5-82. Table 5C-5-82: Drift Header Information Stored Serially in LSB of Amplitudes BITS REQUIRED DESCRIPTION 8 Record type (10 in hexadecimal form, 0x0a for Drift) -1 byte 16 # of bytes in header 8 PREFACE Version Indicator FF (hex) fixed 228 Drift Data PREFACE (57 items) 52 Subcase Header (Next 5 items): Actual Frequency in kHz (5 nibbles) Height in km of Maximum Amplitude Signal for first Subcase (4 nibbles) Height Bin Number (2 nibbles) Automatic Gain Offset 6 dB units of attenuation (in addition to base gain) Polarization (X=0, O=1) 52 Repeat Subcase Headers for all heights (1st freq and polarization) , then store another group of heights for all frequencies, then store another height/freq group for X polarization (if selected) The Drift Data PREFACE structure is shown in Table 5C-5-83. Each PREFACE value is a 4-bit nibble and thus takes four bytes of the spectra amplitudes to be stored. ITEM # Table 5C-5-83: Drift Data Specification DESCRIPTION UNITS RANGE ACCURACY PRECISION TYPE FORMAT 1, 2 Year years 0-99 - - 4-bit BCD 2 digits 3, 4, 5 Day of Year days 1-366 - - 4-bit BCD 4 digits 6, 7 Hour hours 0-23 - - 4-bit BCD 2 digits 8, 9 Minute minutes 0-59 - - 4-bit BCD 2 digits 10, 11 Second seconds 0-59 - - 4-bit BCD 2 digits 12 Schedule # - 1-6 - - 4-bit BCD 1 digit 13 Program - 1-7 - - 4-bit BCD 1 digit (A-G) 14, 15 Drift Data Flag - FF (plain) - - 4-bit hex - FE (1/2 width Doppler shift) A5-45 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL ITEM # DESCRIPTION 16 Journal, J UNITS bitencoded 17 First height of sam- 10 km pling window 18 Height resolution encoded 19 Number of Heights encoded 20 - 25 Start Frequency 100 Hz 26 Disk IO - 27 Frequency Enabled Search - 28. 29 Fine Frequency Step 10 kHz 30 Number of small steps in a scan, S, absolute value 31, 32 Number of small steps in a scan, S 33, 34 Start Frequency, LL 1 Mhz 35 Coarse Frequency encoded Step, or number of repetitions 36, 37 Start Frequency, LL 38 Bottom Height, B 39 Top Height, T 40 Unused 41 - 43 Station ID 44 Phase Code, X 1 Mhz 100 km 100 km - 45 Multi-antenna se- - quencing and O/X polarization options, A RANGE ACCURACY PRECISION TYPE FORMAT bit 0: new gain - - 4-bit hex binary bit 1: new height bit 2: new freq bit 3: new case 00-99 10 km 10 km 4-bit BCD 2 digits 2 - 2.5 5-5 10 - 10 km km 2.5 km km 8 - 0 - 256 128 - 010000 - 450000 1 kHz Ah - 0 1 (yes) (no) - 0-255 10 kHz 0 to 15 - 2.5 km 100 Hz 10 kHz - 4-bit hex binary 4-bit BCD 1 digit 4-bit BCD 6 digits 4-bit hex binary 4-bit BCD 1 digit nibbles of unsigned the 1 byte char binary 4-bit hex binary -15 to +15 negative value means no multiplexing 01 to 45 1 MHz 0 (200 1 (100 2 (50 3 (25 4 (10 5 (5 kHz) kHz) kHz) kHz) kHz) kHz) 1 to 45 1 MHz 0 to 15 100 km 0 to 15 100 km - - 000 to 999 - 1 (complim.) - 2 (short) 3 (75% duty) 4(100% duty) +8 (no phase switch) 0 (sum), - 1-4 (individual antennas), 7 (antenna scan), +8 (only O polari- - 1 MHz - 1 MHz 100 km 100 km - - nibbles of signed the 1 byte char binary 4-bit BCD 2 digits 4-bit BCD 1 digit 4-bit BCD 2 digits 4-bit hex binary 4-bit hex binary - - 4-bit BCD 3 digits 4-bit hex binary 4-bit hex binary A5-46 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL ITEM # DESCRIPTION UNITS RANGE zation) ACCURACY PRECISION TYPE FORMAT 46, 47 CIT length sec 0 - 255 1 sec 1 sec nibbles of unsigned the 1 byte char binary 48 Number of Doppler encoded, 3 - 7 (power of 2) - - 4-bit BCD 1 digit lines, N actual value is power of 2 49 Pulse Repetition Rate, encoded 0 (50 pps) - - 4-bit BCD 1 digit R 2 (100 pps) 3 (200 pps) 50 Waveform, X - 1 (complim.) - - 4-bit hex binary 2 (short) 3 (75% duty) 4 (100% duty) +8 (no phase switch) 51 Delay, D 50 msec 0 - 15 50 msec 50 msec 4-bit hex binary 52 Frequency Search - 0 (no) - - 4-bit BCD 1 digit Enabled, I 1 (yes) 53 Base Gain, G 6 dB 0 - 7 (0 - 42 dB) 6 dB +8 (+auto gain) 6 dB 4-bit hex binary 54, 55 Heights to Output, O - 0 - 255 - - nibbles of unsigned the 1 byte char binary 56 Number of polariza- - 1 or 2 - - 4-bit BCD 1 digit tions 57 Start Gain 6 dB 0 - 15 - - 4-bit hex binary LEGACY SCIENCE DATA FORMATS: SAO The SAO v 4.3 format description can be found publicly at http://ulcar.uml.edu/~iag/SAO-4.3.htm SCIENCE DATA FORMATS: SAO.XML 5.0 The SAO.XML v 5.0 format description can be found publicly at http://ulcar.uml.edu/SAOXML/ A5-47 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL SECTION 6 MAINTENANCE _______________________________________________________________________________ SECTION CONTENTS Page SECTION 6 6-1 CHAPTER 1 SYSTEM MAINTENANCE FEATURES................................................................ 6-3 MAINTENANCE CHARACTERISTICS...................................................................................................... 6-3 PHYSICAL AND ELECTRICAL SPECIFICATIONS .................................................................................. 6-3 SYSTEM POWER...................................................................................................................................... 6-3 POWER MANAGEMENT........................................................................................................................... 6-3 INTERNAL CABLING ................................................................................................................................ 6-6 FRONT PANEL CONNECTORS AND CONTROLS ................................................................................. 6-6 ROUTINE MAINTENANCE TASKS........................................................................................................... 6-7 MAINTENANCE SPARES RECOMMENDATION ..................................................................................... 6-8 BUILT-IN TEST: PERIODIC SELF-DIAGNOSTICS .................................................................................. 6-8 CHAPTER 2 REPLACEMENT OF MODULES ........................................................................ 6-15 ACCESSING OR REPLACING LRM’S IN THE DPS MAIN CHASSIS. .................................................. 6-15 DUAL POWER AMPLIFIER CHASSIS.................................................................................................... 6-16 ANTENNA SUB-SYSTEMS ..................................................................................................................... 6-17 CHAPTER 3 REPAIR OF FAILED MODULES........................................................................ 6-17 TROUBLESHOOTING THE BATTERY INTERFACE BOX..................................................................... 6-18 TROUBLESHOOTING THE RF POWER AMPLIFIER MODULE ........................................................... 6-18 ANNEX A 6-19 PHYSICAL AND ELECTRICAL SPECIFICATIONS (TBR) ..................................................................... 6-19 SECTION 6 MAINTENANCE 6-1 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE List of Figures Figure 6-1: Back-up Battery Connection Configuration Figure 6-2: Power Management (System Power) Figure 6-3: Power Management (BIT Card Interface) Figure 6-4: Internal Power Dependency Figure 6-5: BIT Sensor Locations Figure 6-6: BIT Case 1 – External Loopback Figure 6-7: BIT Case 2 – Internal Loopback Figure 6-8: BIT Case 3 – Internal Loopback without trackers Figure 6-9: BIT Case 4 – Transmission into dummy loads Figure 6-10: BIT programs has to be scheduled Figure 6-11: Built-In Test display Figure 6-12: Built-In Test Report (update to LRM) Figure 6-13: Digisonde Upper Chassis Figure 6-14: PA Chassis List of Tables Table 6-1: Signal and Power Buses Table 6-2: Front Panel Connectors And Controls Table 6-3: Air Filter Maintenance Table 6-4: Maintenance Spares Recommendation Table 6-4: BIT Faults of the Dual Power Amplifier Chassis Table 6-4: BIT Faults of the Receive and Transmit Antenna Sub-system DIGISONDE 4D SYSTEM MANUAL 6-4 6-5 6-5 6-6 6-10 6-11 6-11 6-12 6-12 6-13 6-14 6-14 6-15 6-17 6-6 6-7 6-7 6-8 6-16 6-17 6-2 SECTION 6 MAINTENANCE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL CHAPTER 1 SYSTEM MAINTENANCE FEATURES MAINTENANCE CHARACTERISTICS 601. The Digisonde™ Portable Sounder and associated sub-systems have been designed to provide high availability with the least possible demand on human intervention to attend to maintenance tasks. Preventative maintenance tasks are restricted to replacement of air-filters and ensuring that cable terminations and exposed hardware are kept clean. Corrective maintenance tasks initiated by BIT detection of a fault are also described. PHYSICAL AND ELECTRICAL SPECIFICATIONS 602. The physical and electrical specifications of the sounder and line replaceable units (LRU) and modules (LRM) are listed in Annex A. SYSTEM POWER 603. Input power specifications for the sounder are:  Power Supply (Kepco RKW 28-23K)  Input: Nominal 120/240; Range 85-265 VAC  Output: Nominal 28 VDC @ 23.0 Amp at Temperature -10 to 50 C; Range 19.6 – 33.6 VDC  AC input line filter (Corcom 10VN1) POWER MANAGEMENT 604. Figure 6-1 shows the wiring requirements for the correct connection of the back-up battery to the sounder. Two user supplied 12 volt batteries are connected in series to provide the 24 VDC to the sounder power distribution card in case of mains voltage failure. The system socket connects the system battery input cable to the battery input jack while the chassis socket connects the DC terminal strip to the main chassis. The RF power amplifier receives its power via this external battery cable. On the following pages, Figure 6-2 and Figure 6-3 provide a schematic view of the power management system; Figure 6-4 shows the internal power dependency schematic. SECTION 6 MAINTENANCE 6-3 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 6-1: Back-up Battery Connection Configuration 6-4 SECTION 6 MAINTENANCE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 6-2: Power Management (System Power) Figure 6-3: Power Management (BIT Card Interface) SECTION 6 MAINTENANCE 6-5 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 6-4: Internal Power Dependency 605. A 30 A fuse is provided in line between the batteries and the battery interface, also the sounder is protected by a 7.5 A circuit breaker in the main chassis, and a 30 A fuse in the power amplifier chassis. INTERNAL CABLING 606. Internal signal and power distribution has been logically divided into functional buses as shown in Table 6-1. Table 6-1: Signal and Power Buses BUS FUNCTION BACKPLANE REFERENCE A-Bus control bus for the receive antennas switches P17 P-Bus connection between the control computer parallel port and the P13 sounder custom hardware mounted in the card cage via the Digital Transmitter/Timing card IDE-Bus (DMA) connects the system’s pre-processor card to the control computer P19 F-Bus control bus for the power amplifier P14 Power Bus supplies power to the card cage and antennas switches P16 BIT I/O Bus conducts BIT sensor information P20 FRONT PANEL CONNECTORS AND CONTROLS 6-6 SECTION 6 MAINTENANCE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 607. The functions of and circuit references for the front panel coaxial connectors and controls are listed in Table 6-2. Table 6-2: Front Panel Connectors And Controls ITEM FUNCTION CONNECTOR REFERENCE TRIG Scope Trigger Signal for RF transmissions BCK-P15 RXIF Not Used / Spare N.A. TX1 Digital Transmitter Channel 1 to RF Amp XMT-P4 TX2 Digital Transmitter Channel 2 to RF Amp XMT-P8 TX ON Output transmitter ON pulse BCK-P21 SYSTEM RESET Momentary push button. Triggers system reset pulse BCK-P15 ROUTINE MAINTENANCE TASKS 608. Except for routine attention to cleanliness of the air intake system, no periodic maintenance tasks are required. The six air filters should be maintained as shown in Table 6-3. LOCATION Table 6-3: Air Filter Maintenance NO. PERIODICY MAINTENANCE TASKS Sounder enclosure Ex- 2 panded metal type. Inspect twice a year if possible and during every site visit. Examine for build-up of dust. If present, wash the filters with mild detergent solution, and dry and refit. Rear of main chassis. Syn- 1 thetic foam type. Inspect twice a year if possible and during every site visit. Wash in mild detergent solution or discard and replace if damaged. Rear of PA chassis. Syn- 2 thetic foam type. Inspect twice a year if possible and during every site visit.. Wash in mild detergent solution or discard and replace if damaged. 609. To remove the expanded metal air filters: Pull the RF Amp chassis forward or remove it entirely (see section 6.5). Remove the three nuts on the front side of the filter carrier and slide the filter out. The filters fit in the carrier somewhat tightly and a screwdriver may be necessary to assist in the filter removal. 610. To remove the main chassis foam filter: Remove the rear cover of the DPS chassis by turning the four fastener knobs counter-clockwise. Locate the fan filter on the rear panel. Unclip the plastic filter holder that clips over the edges of the fan. Remove the holder and take the filter out. 611. To remove the RF chassis foam filters: Pull the RF Amp chassis fully forward or remove it entirely (see section 6.5). Locate the fan filter on the rear panel. Unclip the plastic filter holder that clips over the edges of the fan. Remove the holder and take the filter out. SECTION 6 MAINTENANCE 6-7 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL MAINTENANCE SPARES RECOMMENDATION 612. A listing of recommended maintenance spares showing manufacturer’s part number, quantity fitted in the system, recommended support sparing level, and recommended maintenance policy is provided in Table 6-4. It is recommended that spares be held in appropriate locations to support fielded systems in accordance with the overall system maintenance support plan. MANUFACTURER/ PART NO. Table 6-4: Maintenance Spares Recommendation LRM NOMENCLATURE QTY FITTED SUGSTD QTY SPARED REFERENCE THIS MANUAL SECTION TO REPLACE THE LRM Commell, HS-872PEDG2 UMLCAR #5021107 UMLCAR #5021105 UMLCAR #5021104 UMLCAR #5021301 UMLCAR #5021108 UMLCAR #5021202 UMLCAR #7020103 UMLCAR #7040010 Twin Industries 8196-EXT Seagate Sony NMB EMB3610KL DELTA AFB0624HH QUALTEK BUSS MOTOROLA XICON PCB, Computer 2 PCB, Tracker 4 PCB, Receiver 1 PCB, Digital Transmitter 1 PCB, Pre-processor 1 PCB, BIT 1 PCB, Power Distribution 1 ASSY, Antenna Switch 1 ASSY, Antenna Preamp 4 PCB, Extender Card N/A Hard Drive 1 DVD/CD Rewritable Drive 1 Fan, Axial, 92 mm 1 Fan, Axial, 60 mm 2 Filter, Air, Polyurethane, 92 3 mm 15A, 30A 1/ EACH MRF-141G 4 GAIN RESISTOR SET N/A 1 1 1 1 1 1 1 1 1 1 1 1 1 2 3 1/ EACH 1 1 6-15 6-16 6-16 6-16 6-16 6-16 6-15 6-16 N/A 6-15 6-15 6-15 6-15 6-15 BUILT-IN TEST: PERIODIC SELF-DIAGNOSTICS 613. The Built-In Test diagnostic system is comprised of a set of hardware sensors, a BIT card with a microcontroller that digitizes the sensor data, and the BIT program software. The BIT program also uses measurement data in addition to the data collected by the BIT card to determine the health of the system. There are three types of BIT sensors. Digital (Go/No Go) sensors are used to monitor power supplies and over-temperature conditions. Static Analog sensors are analog signals that are always present such as temperature signals. Dynamic Analog sensors are signals that are present only during sounding. Sensors collected by the BIT Card:  Power Distribution card power for Preamplifier/Polarization Box (digital) 6-8 SECTION 6 MAINTENANCE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL  Power Distribution card –15V, -5V, +3.3V, +15V, +12V(digital)  Power Distribution card over-temperature condition (digital)  Power Amplifier power for first stage amplifier +18V (digital)  Transceiver Chassis Temperature (static analog)  Power Amplifier Chassis Temperature (static analog)  Transmitter card channel 1 & 2 output (dynamic analog)  RF Power Amplifier channel 1 & 2 output (dynamic analog)  Saturation sensor from Tracker #4 (digital) Other measurement data collected and used by the BIT program:  Receiver card channel 1, 2, 3, 4 output (dynamic analog, “routine data”)  Hardware Test Pattern from Pre-Processor (digital, gathered by DESC)  Parallel Bus Data Timeouts (digital, determined by DESC) 614. Figure 6-5 shows the location of the sensors and data collection points. Red circles are hardware sensors. Blue circles show data collection points. 615. The BIT program puts the system in four different configurations (cases) using switches in the antenna switch, tracker cards, and RF amplifier output switching to make a determination about system health. 616. Case 1 is external loopback. The system transmits normally as though making a measurement. The signal enters the receivers through the antenna. The program listens at 0 km height for the transmit pulse. 617. Case 2 is internal loopback. A low level calibration signal from the digital transmitter is routed through the antenna switch to the inputs of the tracker cards. 618. Case 3 is internal loopback with tracker cards bypassed. A low level calibration signal from the digital transmitter is routed through the antenna switch to the inputs of the tracker cards. Switches on the tracker cards connect the inputs to the outputs, effectively bypassing the bandpass filters. 619. Case 4 is transmission into dummy loads. The system transmits normally but the RF output from the half octave filters in the power amplifier are routed to dummy loads rather than the transmit antenna. The health of the transmit antenna can be determined by comparing the levels of the RF 1 & 2 sensors with the results from Case 1. SECTION 6 MAINTENANCE 6-9 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 6-5: BIT Sensor Locations 6-10 SECTION 6 MAINTENANCE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 6-6: BIT Case 1 – External Loopback Figure 6-7: BIT Case 2 – Internal Loopback SECTION 6 MAINTENANCE 6-11 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 6-8: BIT Case 3 – Internal Loopback without trackers Figure 6-9: BIT Case 4 – Transmission into dummy loads 620. BIT is a program that has to be scheduled (see Figure 6-10). It should be included in the routine sounding schedule. It can also be manually run in “Diagnostic” mode from the DCART’s Program screen. BIT data 6-12 SECTION 6 MAINTENANCE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL can be viewed in two forms: a Built-In Test display and a BIT Report. The Built-In test display is accessed from a tab in the DCART menus. It displays the sensor’s mnemonic, name, measurement data, go/no go status, and the limits used for the go/no go decision (see Figure 6-11). Figure 6-10: BIT programs has to be scheduled 621. At the upper right of the Built-in Test display is a “Report” button. If the button is pressed a BIT report is displayed (see Figure 6-12). The BIT report is designed to help isolate the Line Replaceable Module (LRM) in the case of a failure. The BIT report provides the following information:  Shows a system failure if one occurs  Lists suspected components  Provides troubleshooting recommendations  Lists failed sensors, including “case” where failure occurred  Lists hardware by state; GO, NOGO, UNKNOWN  Lists sensor definitions 622. The BIT report can also be accessed remotely from the system’s web page through the main menu. SECTION 6 MAINTENANCE 6-13 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 6-11: Built-In Test display Figure 6-12: Built-In Test Report (update to LRM) 6-14 SECTION 6 MAINTENANCE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE CHAPTER 2 REPLACEMENT OF MODULES DIGISONDE 4D SYSTEM MANUAL ACCESSING OR REPLACING LRM’S IN THE DPS MAIN CHASSIS. NOTE: A ground strap should be worn when handling LRM’s to avoid damaging them by electrostatic discharge (ESD) 6.1 Access to Main Chassis 6.1.1 Shut off power. 6.1.2 Remove DPS enclosure front cover by turning the four fastener knobs counter-clockwise. 6.1.3 Remove the four panel mount screws at left and right sides of DPS main chassis front panel. 6.1.4 Slide the main chassis forward (toward you) until slides lock. 6.1.5 Remove the top cover by loosening six #6-32 screws at the top left and right sides of the main chassis. 6.1.6 Locate the LRM to be replaced (see Figure 6-13). The Tracker, Digital Receiver, Pre- processor, Digital Transmitter, and BIT cards are located in the card cage. The card cage is silk screened to show the locations of the individual cards. Figure 6-13: Digisonde Upper Chassis 6.2 Power Distribution card. SECTION 6 MAINTENANCE 6-15 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 6.2.1 6.2.2 6.2.3 6.2.4 6.2.5 6.2.6 6.2.7 Press slide lock button on right hand side of chassis and push the slide toward the rear of the chassis until the inner part of the slide is disengaged. Locate Power Distribution card. (see Figure 6-13). Disconnect all cable connections. Remove 15 #4-40 mounting screws from side panel of Main Chassis. Remove suspect Power Distribution card. Remove thermal gasket between heat sink surfaces of replacement card and right side panel. Repeat steps (6.1.1 - 6.1.7) in reverse order to replace Power Distribution card. 6.3 Tracker, Digital Receiver, Pre-processor, Digital Transmitter, and BIT cards. 6.3.1 Locate the card cage in the DPS Main Chassis (see Figure 6-13). 6.3.2 Locate the LRM to be replaced (see silkscreen on edge of card cage). 6.3.3 Remove any interconnect cables at top edge of board assembly to be replaced. 6.3.4 Remove suspect LRM. 6.3.5 Replace LRM and re-attach cables. 6.4 Antenna Switch. 6.4.1 Release chassis slide locks and slide Main Chassis out far enough to gain access to the rear of the Main Chassis. 6.4.2 Locate Antenna Switch LRM. 6.4.3 Remove 4 cables at rear of chassis marked ANT1- ANT4. 6.4.4 Remove J1, CAL IN and RF OUT connections from Antenna Switch. 6.4.5 Remove 4 #6-32 screws at rear of chassis. 6.4.6 Repeat steps (6.4.1 - 6.4.5) in reverse order to replace Antenna Switch assembly. DUAL POWER AMPLIFIER CHASSIS 623. Table 6-5 lists BIT faults pertaining to the Dual Power Amplifier Chassis. Upon detection the PA chassis should be replaced and repair concluded at depot level. Equipment needed: #1 Philips and flat head screwdriver Table 6-5: BIT Faults of the Dual Power Amplifier Chassis BIT Sensor Fault Condition Remarks RF1 NO-GO --- RF2 NO-GO --- +18V NO-GO --- Amp Temp NO-G0 Thermal protection shutoff, threshold adjustable in StationSpecific.udd 6.5 Removal procedure for Dual RF Power Amplifier (PA) Chassis 6.5.1 Remove DPS enclosure front cover by turning the 4 fastener knobs counter-clockwise. 6.5.2 Remove four panel mount screws at left and right sides of PA chassis front panel. 6.5.3 Slide PA chassis out of enclosure until slides lock. 6.5.4 Disconnect all cables from rear of PA chassis. 6.5.5 Press in slide lock buttons and remove PA chassis from enclosure. 6.5.6 To replace PA chassis repeat steps 1-5 in reverse order. 6-16 SECTION 6 MAINTENANCE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL Figure 6-14: PA Chassis ANTENNA SUB-SYSTEMS 624. Table 6-6 lists BIT faults (refer to Go/NoGo Matrix Figure 7-15) pertaining to the Receive and Transmit Antenna sub-systems. Equipment needed: None Table 6-6: BIT Faults of the Receive and Transmit Antenna Sub-system BIT Sensor Condition Remarks Fault RxAnt NO-GO Fault occurs when an RX antenna is faulty. TxAnt NO-GO Fault occurs when VSWR mismatch is detected on either TX antenna 625. Periodic evaluation of RX Antenna sub-systems is performed by the BIT program. If a bad channel is indicated, cables from the receive antennas can be swapped on the rear panel of the DPS to check for a bad cable or antenna preamp; however, they must be returned to their original positions once the antenna has been repaired to ensure the Drift (.dft) data displays correct directional information. O/X switching voltage (17-22 VDC) can be measured at the antenna preamp on the N-type connector. No voltage can indicate a break in the receive cable. If a TDR is available it may be used to locate the cable break. REPAIR OF FAILED MODULES SECTION 6 MAINTENANCE 6-17 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL 626. LRM maintenance will normally be performed under special arrangements with the manufacturer. The LRM to be diagnosed may have been found faulty by the Built-In Test at the operating site, or by finding that replacement of the LRM returned the system to normal operating status. To assist with the identification of discrete components and non-specialised fault finding on proprietary circuit boards, a technical data package comprised of circuit board layouts, parts lists, and schematics is provided separately to the customer. 627. Due to the small size and density of the integrated circuits on the LRM’s in the main chassis, it is recommended that the boards be diagnosed and repaired by the manufacturer. Without proper tools and experience it is easy to damage these boards. 628. It is possible for a customer to test and repair some of the modules outside the main chassis. Diagnostic procedures are included in the following paragraphs. TROUBLESHOOTING THE BATTERY INTERFACE BOX Special Test Equipment: Digital Multimeter Reference Documents: Battery Interface Schematic SC-7010101-01 Test Components: 629. The battery interface provides a smooth transition during power outages by: 1. Opening up the power connection to the Main Chassis and RF Amplifier chassis in the event of an overvoltage (>31V) or undervoltage (<21V) condition, or and overcurrent (>45A) condition. 2. Delaying reapplication of the power for 5 sec in the case of a protective shutdown. 3. Providing a voltage readout for manual monitoring of aging batteries. 630. Under normal operating conditions, if a voltage between 22 and 30V is present at battery terminals BT1 & BT2 this voltage should be conducted to the output at BT3 & BT4. If not, check that the Q7 regulator output is +15V and the reference voltage at R32 and R36 is 9V and that +15V power and Gnd are applied to U3 pin 3 and pin 12. Next check that the reference voltages at R34, R39 and R52/53/54 are correct. They should read: R34 = 11V R39 = 14.5V and R52 = 8.1V 631. If all are functional, short across C32 and see if the output voltage appears. If so, replace U3. If LED D2 does not light with C32 shorted, check and replace D2, R41 and R42. If the LED still does not light the FETs, Q4 and Q5, are probably bad and should be replaced. TROUBLESHOOTING THE RF POWER AMPLIFIER MODULE Special Test Equipment: 100MHz Oscilloscope Reference Documents: RF Power Amplifier Schematics SC-7031101-01 632. The RF Amplifier card comprises two independent (referred to below as the two channels), three stage wideband amplifiers. The entire 10 inch x 6 inch board is mounted to a 10 inch by 6 inch heat sink. The input voltage is the system’s primary power of 25 to 28VDC, from the power supply and batteries in parallel, via the battery interface box which contains FET switches which will open if an over-current or over or under voltage condition occurs. The primary power is applied at the output end of the AMP board where it feed power to the 300V output stages. It is also routed back off the board to a twisted pair which runs down the underside (the fin side) of the heat sink to feed power to the small signal end of the board. Keeping this twisted pair on the back 6-18 SECTION 6 MAINTENANCE DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE DIGISONDE 4D SYSTEM MANUAL side of the AMP heat sink reduces coupling between output and input, thus reducing the danger of a positive feedback situation. 633. The input signal to each amplifier channel is 1.7Vp-p, falling off slightly at the higher frequencies. The input cable is terminated in a PI attenuator made up of a 68, 330, and 68 ohm resistors where the 330ohm is bypassed by a 47pF capacitor to boost up the high frequency output. The input signal is amplified to 12-14V by A1/A2 (36dB gain 500kHz to 500MHz amplifier modules), which can be probed at the input of T7/T15. As a quick check, the output of T9/17 can be probed at the input of the series resistors R124/126 or R204/206. There should be 20-25Vp-p at this point. Then the output voltage 240-300Vp-p can be probed at the vertical wire connection (from T13/T21 to the PC board trace) at the output of T13/T21. 634. The critical setting in the RF AMP is the bias voltage set by R67/147 for the input stages and R107/187 for the output stages. This bias voltage is pulsed, rising when the R BNC signal (Xmtr On from the front panel input from the upper chassis) rises. The R BNC, via U41 and Q52/53 also applies the regulated +18V to amplifiers A1 and A2. For waveform 1 this is 750usec every 5, or 10msec, so the bias voltage level can only be measured by probing it with an oscilloscope. The bias voltage should be set to draw 2 to 4A idle current for the input stages U8 and U16, and 0.75 to 1.5A for the output stage, U12 and U20, when no input signal is applied (see procedure below). Since much larger signals are fed to the output stage it is somewhat self-biasing and does not need a high bias level. If the system will be used for CW transmission (waveform 4) the setting should be 2A or less. The bias level is given in amps of idle current rather than a voltage since the turn-on voltage for various batches of MRF-141G MOSFET transistors varies widely. An initial setting of 2.4V for pulsed operation, and 2.0V for CW should be a safe starting point for all production lots of these devices. The bias level can be probed by test points at C72/152 and at C109/189. 635. Once an initial bias voltage level has been set, or if checking out an operating AMP, the system should be operated with 50ohm terminators connected to the front panel Xmt1 and Xmt2 inputs. Attaching two probes, one on each side of the surge limiting resistors R60/600, and setting the oscilloscope to an A-B display, multiply the voltage drop observed by 10 (R60/600 is 0.1ohm) to get the idle current. Similarly, checking across R131/219 and multiplying by 20 gives the idle current in the output stage. If no A-B setting is available, the voltage referenced to ground can be probed on each side of the resistors and the subtraction performed on paper. If adjustment is necessary, turning the 15-turn potentiometers (R67/147/107 and 187) CCW increases the voltage and CW decreases the voltage, at about 0.3V/turn. 636. Since the MRF-141G device is a matched pair of FETs it is possible that only one has failed. If a stage is biased properly but does not make the gain it should, then check that a very similar signal can be detected at each drain (output) tab on the suspected MRF-141. If the entire device has shorted, the 27V from the drain often feeds through to the gate (the input tab) which should normally have the 2.4V bias pulse on it. If this is the case replace the FET. ANNEX A PHYSICAL AND ELECTRICAL SPECIFICATIONS (TBR) Table 6A-1 Physical and Electrical Attributes SYSTEM ASSEMBLY VOLTS CURRENT POWER Digital Transmitter Card +5 0.3 A 1.5 W +15 0.02 0.3 WEIGHT (KG) 0.11 SECTION 6 MAINTENANCE 6-19 DISTRIBUTE ONLY IN ACCORDANCE WITH RESTRICTIONS ON COVER PAGE Digital Receiver Card +5 15 Pre-Processor Card +5 +15 BIT Card +5 +15 Tracker Card 15 Backplane Power Distribution Card +24 Polarization Switches (x4) +24 Enclosure & Cables SP Card +5 Core Duo Computers (each) 5 12 Disk & Tape Drives +5 +12 (Spin-up Surge) +12 Fan x 6 +24 Frequency Standard +24 RF Amp (heat sink PCB) +24 Half Octave Filters x 2 Power Supply Power Amp Chassis (non-pop.) Main Chassis (non-pop.) ECS Enclosure (non-pop.) Rear I/O Panel & Connectors TOTAL * Supplied from batteries. +24 230 VAC DIGISONDE 4D SYSTEM MANUAL 0.1 0.5 0.11 0.1 1.5 0.2 1.0 0.11 0.16 2.5 0.3 1.5 0.09 0.1 1.5 0.2 1.5 0.11 0.68 3.6 75.0 1.12 0.06 1.5 0.04 0.5 0.4 2.0 0.14 5.0 25.0 0.45 0.25 1.25 1.1 0.2 0.6 1.0 12 0.69 16.5 0.48 0.88 21 0.55 3.75 (Avg) 90 2.34 0.2 (Standby) 5 30 (Peak) 720* 0.1 2.4 1.1 2.25/1.13 206.5 5.5 4.5 6.0 23.6 1.8 206.5 52.5 Enclosure Assembly Chassis Assembly RF Amp Chassis Assembly Table 6A-2 Critical Dimensions HEIGHT (MM) WIDTH (MM) DEPTH (MM) 464 178 133.5 586 482.5 482.5 846 584 406.5 WEIGHT(KG) 30.65 13.56 8.29 6-20 SECTION 6 MAINTENANCE

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