PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = "MGN" INSTRUMENT_ID = "RDRS" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "RADAR SYSTEM" INSTRUMENT_TYPE = "RADAR" INSTRUMENT_DESC = " Instrument Specifications ========================= The radar was manufactured by Hughes Aircraft Company and the 'build date' is taken to be 1989-01-01. The radar dimensions were 0.304 by 1.35 by 0.902 (height by length by width in meters) and the mass was 126.1 kg. Instrument Id : RDRS Instrument Host Id : MGN Pi Pds User Id : GPETTENGILL Instrument Name : RADAR SYSTEM Instrument Type : RADAR Build Date : 1989-01-01 Instrument Mass : 126.100000 Instrument Length : 1.350000 Instrument Width : 0.902000 Instrument Height : 0.304000 Instrument Manufacturer Name : HUGHES AIRCRAFT For more information on the radar system see the papers by [JOHNSON1990] and [SAUNDERSETAL1990]. Instrument Overview =================== The Magellan radar system included a 3.7 m diameter high gain antenna (HGA) for SAR and radiometry and a smaller fan-beam antenna (ALTA) for altimetry. The system operated at 12.6 cm wavelength. Common electronics were used in SAR, altimetry, and radiometry modes. The SAR operated in a burst mode; altimetry and radiometry observations were interleaved with the SAR bursts. Between SAR bursts (typically several times a second) groups of altimeter pulses were transmitted from a dedicated fan-beam altimeter antenna directed toward the spacecraft's nadir. The altimeter pulses were identical in waveform and bandwidth to the SAR pulses, resulting in a range accuracy of better than 15 m. The pulse-repetition rate and burst duration differed between the two modes. Radiometry data were obtained by spending a portion of the time between SAR bursts and after altimeter operation in a passive (receive-only) mode, with the HGA antenna capturing the microwave thermal emission from the planet. Noise power within the 10-MHz receiver bandwidth was detected and accumulated for 50 ms. To reduce the sensitivity to receiver gain changes in this mode, the receiver was connected on alternate bursts first to a comparison dummy load at a known physical temperature and then to the HGA. The short-term temperature resolution was about 2 K; the long-term absolute accuracy after calibration was about 20 K. Science Objectives ================== See MISSION_OBJECTIVES_SUMMARY under MISSION. Operational Considerations ========================== The Magellan radar system was used to acquire radar back-scatter (SAR) images, altimetry, and radiometry when the spacecraft was close to the planet. Nominal operation extended from about 20 minutes before periapsis until about 20 minutes after periapsis. In the SAR mode output from the radar receiver was sampled, blocks of samples were quantized using an adaptive procedure, and the results were stored on tape. In the altimetry mode samples were recorded directly, without quantization. Radiometry measurements were stored in the radar header records. During most of the remainder of each orbit, the HGA was pointed toward Earth and the contents of the tape recorder were transmitted to a station of the DSN at approximately 270 kilobits/second. SAR, altimetry, and radiometry data were then processed using ground software into images, altimetry profiles, estimates of backscatter coefficient, emissivity, and other quantities. Calibration Description ======================= The radar was calibrated before flight using an active electronic target simulator [CUEVAS1989]. Platform Mounting Descriptions ============================== The spacecraft +Z axis vector was in the nominal direction of the HGA boresight. The +X axis vector was parallel to the nominal rotation axis of the solar panels. The +Y axis vector formed a right-handed coordinate system and was in the nominal direction of the star scanner boresight. The spacecraft velocity vector was in approximately the -Y direction when the spacecraft was oriented for left-looking SAR operation. The nominal HGA polarization was linear in the y-direction. Cone Offset Angle : 0.00 Cross Cone Offset Angle : 0.00 Twist Offset Angle : 0.00 The altimetry antenna boresight was in the x-z plane 25 degrees from the +Z direction and 65 degrees from the +X direction. The altimetry antenna was aimed approximately toward nadir during nominal radar operation. The altimetry antenna polarization was linear in the y-direction. The medium gain antenna boresight was 70 degrees from the +Z direction and 20 degrees from the -Y direction. The low gain antenna was mounted on the back of the HGA feed; it's boresight was in the +Z direction and it had a hemispherical radiation pattern. Principal Investigator ====================== The Principal Investigator for the radar instrument was Gordon H. Pettengill. Instrument Section / Operating Mode Descriptions ================================================ The Magellan radar system consisted of the following sections, each of which operated in the following modes: Section Mode ------------------------------------------- SAR Synthetic Aperture Radar (SAR) ALT Altimetry RAD Radiometry (1) SAR Characteristics ----------------------- In the Synthetic Aperture Radar mode, the radar transmitted bursts of phase-modulated pulses through its high gain antenna. Echo signals were captured by the antenna, sampled at the receiver output, and stored on tape after being quantized to reduce data volume. Pulse repetition rate and incidence angle were chosen to meet a minimum signal-to-noise ratio requirement (8 dB) for image pixels after ground processing. Multiple looks were used in processing to reduce speckle noise. Incidence angles varied from about 13 degrees at the pole to about 44 degrees at periapsis during normal mapping operations (e.g., Cycle 1); but other 'look angle profiles' were used during the mission. Peak transmit power : 350 watts Transmitted pulse length : 26.5 microsecs Pulse repetition frequency : 4400-5800 per sec Time bandwidth product : 60 Inverse baud width : 2.26 MHz Data quantization (I and Q) : 2 bits each Recorded data rate : 750 kilobits/sec Polarization (nominal) : linear horizontal HGA half-power full beam width : 2.2 deg (azimuth) : 2.5 deg (elev) one-way gain (from SAR RF port) : 35.7 dBi System temperature (viewing Venus) : 1250 K Surface resolution (range) : 120-360 m (along track) : 120-150 m Number of looks : 4 or more Swath width : 25 km (approx) Antenna look angle : 13-47 deg Incidence angle on surface : 18-50 deg Data Path Type : RECORDED DATA PLAYBACK Instrument Power Consumption : UNK (2) ALT Characteristics ----------------------- After SAR bursts (typically several times a second) groups of altimeter pulses were transmitted from a dedicated fan beam altimeter antenna (ALTA) directed toward the spacecraft's nadir. Output from the radar receiver was sampled, and the samples were stored on tape for transmission to Earth. During nominal left-looking SAR operation the ALTA pointed approximately 20 deg to the left of the spacecraft ground track at periapsis and about 10 deg to the right of the ground track near the north and south pole. Data quantization (I and Q) : 4 bits each Recorded data rate : 35 kbs Polarization : linear ALTA half-power full beamwidth (along track): 11 deg (cross track): 31 deg one-way gain referenced to ALT RF port : 18.9 dBi ALTA offset from HGA : 25 deg Burst interval : 0.5-1.0 sec duration : 1.0 millisec Dynamic range : 30 dB (or more) Data Path Type : RECORDED DATA PLAYBACK Instrument Power Consumption : UNK (3) RAD Characteristics ----------------------- Radiometry measurements were made by the radar receiver and HGA in a receive-only mode that was activated after the altimetry mode to record the level of microwave radiothermal emission from the planet. Noise power within the 10-MHz receiver bandwidth was detected and accumulated for 50 ms. To reduce the sensitivity to receiver gain changes in this mode, the receiver was connected on alternate bursts first to a comparison dummy load at a known physical temperature and then to the HGA. The short-term temperature resolution was about 2 K; the long-term absolute accuracy after calibration was about 20 K. At several times during the mission, radiometry measurements were carried out using known cosmic radio sources. Receiver Bandwidth : 10 MHz Integration Time : 50 millisecs Polarization (nominal) : linear horizontal Data Quantization : 12 bits Data Rate : 10-48 bits/sec HGA half-power full beam width : 2.2 deg System temperature (viewing Venus) : 1250 K Antenna look angle : 13-47 deg Incidence angle on surface : 18-50 deg Surface resolution (along track) : 15-120 km (cross track) : 20-125 km Data Path Type : RECORDED DATA PLAYBACK Instrument Power Consumption : UNK " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "CUEVAS1989" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "JOHNSON1990" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "SAUNDERSETAL1990" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END