urn:nasa:pds:context:instrument:orad.p12 1.0 1.7.0.0 Product_Context 2016-10-01 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model urn:nasa:pds:context:instrument_host:spacecraft.p12::1.0 instrument_to_instrument_host Pioneer Venus Orbiter Radar Mapper (ORAD) user's manual, Hughes Aircraft Company, Ref. No. D4232, December 1977. reference.HACREF1977 Pettengill, G.H., D.F. Horwood, and C.H. Keller, Pioneer Venus Orbiter Radar Mapper: design and operation, IEEE Trans. Geosci. Remote Sens., GE-18, 28-32, 1980. reference.PETTENGILLETAL1980A ORBITING RADAR Radio-Radar not applicable not applicable INSTRUMENT: ORBITING RADAR SPACECRAFT: PIONEER VENUS ORBITER Instrument Information ====================== Instrument Id : ORAD Instrument Host Id : P12 Pi Pds User Id : PFORD Instrument Name : ORBITING RADAR Instrument Type : RADAR MAPPER Build Date : 1977 Instrument Mass : 9.700000 Instrument Length : 0.240000 Instrument Width : 0.305000 Instrument Height : 0.165000 Instrument Serial Number : 5970-02 Instrument Manufacturer Name : HUGHES AIRCRAFT Instrument Description ====================== The Pioneer Venus radar mapper consisted of a 38 cm antenna and a radar transmitter/receiver, and was flown on the Pioneer 12 orbiter. It functioned continuously from December 5th 1978 until March 23 1981 when it was switched off because spacecraft periapsis had risen to such an extent that no further useful data could be obtained. The antenna could be rotated in one plane by means of a stepping motor that was commanded by the radar system. During a periapsis pass, the antenna was moved so that it pointed to the nadir at some point during each 12 second spacecraft rotation period. The radar was loaded from the ground with approximately 200 commands before each mapping pass, and then operated automatically. The commands included interpolation coefficients that set the altimeter range window, the receiver band-pass filter, and the receiver gain. The instrument was capable of making up to 8 observations during each 12 second period: space calibration, 1 or 4 altimetry measurements, 0, 1 or 2 imaging measurements, and a planet calibration. The number of altimetry and image measurements depended on spacecraft altitude and the downlink bandwidth allotted to the radar instrument. Initial altimetry and imaging data processing was performed on-board. Altimetry echoes were detected, sampled, and correlated against the transmitted waveform, a shift-register sequence, and sub-summed for repeated pulses. Imaging echoes were detected, sampled, and Fourier transformed to achieve azimuth resolution. Science Objectives ================== The radar mapper was designed to obtain a near global picture of the topography, meter-scale surface slopes and reflectivity of Venus. Constraints imposed by the choice of orbit limited the radar coverage to a latitude band lying between 74 degrees N and 61 degrees S completely around the planet. In addition to the altimetry objectives, the experiment sought an image of the radar scattering properties of the surface at oblique incidence. Sensitivity limited the imaged region to a band around the planet lying between 45 degrees N and 10 degrees S. Altimetric error was less than 200 meters; altimetric surface 'footprint' size varied from about 10 km in diameter at a spacecraft altitude of 200 km, to 50 km at a maximum altitude of 4700 km. Imaging resolution varied from 20 to 40 km, depending on spacecraft altitude. Operational Considerations ========================== (1) Shortly after it began operating, a failure was observed in telemetry from the instrument that affected all altimetric and imaging data. This was traced to a circuit failure in the data formatter sub-system, and was totally eliminated by operating the radar on a shortened duty cycle, viz. that all power to the radar was switched off except for a 2 hour period each day. This proved entirely successful, although about 36 days of data were lost while the problem was being diagnosed. (2) It was originally intended that, when the radar was performing 4 altimetry measurements per spacecraft rotation period, they should be made with varying receiver frequencies, thereby 'squinting' the altimeter footprints ahead of, and behind, the nadir point. This proved to be unwise, since the squinted echoes had very low signal strength, so, after approximately 3 months of operation, the radar was commanded no to vary the receiver frequency and the 4 altimeter measurements represented essentially the same surface footprint. Calibration Description ======================= The instrument was calibrated by means of a radar target simulator that was specially built by Hughes, and end-to-end tests of the radar system were conducted on several occasions, including the on-stand test shortly prior to launch. The results were published in the Hughes instrument manual. In Venus orbit, the instrument was calibrated once per 12 second spacecraft rotation period by recording the receiver voltage at that time when the antenna pointed to the zenith, i.e. to cold sky. Section 'ALT' ============= Total Fovs : 0 Data Rate : 24.000000 Sample Bits : 10 'ALT' Detectors --------------- PVORADANT 'ALT' Electronics ----------------- PVORADCTL In modes -------- HAA IM1 IM2 'ALT' Section Parameter 'RADAR ECHO POWER' ------------------------------------------ That part of the transmitted power scattered by the target and received by the radar antenna. Instrument Parameter Name : RADAR ECHO POWER Sampling Parameter Name : TIME Instrument Parameter Unit : WATTS Minimum Sampling Parameter : 0.009000 Maximum Sampling Parameter : 0.030000 Sampling Parameter Interval : 0.000004 Sampling Parameter Resolution : 0.000004 Sampling Parameter Unit : SECOND Section 'IMG' ============= Total Fovs : 0 Data Rate : 309.000000 Sample Bits : 10 'IMG' Detectors --------------- PVORADANT 'IMG' Electronics ----------------- PVORADCTL In modes -------- IM1 IM2 'IMG' Section Parameter 'RADAR ECHO POWER' ------------------------------------------ That part of the transmitted power scattered by the target and received by the radar antenna. Instrument Parameter Name : RADAR ECHO POWER Sampling Parameter Name : TIME Instrument Parameter Unit : WATTS Minimum Sampling Parameter : 0.009000 Maximum Sampling Parameter : 0.030000 Sampling Parameter Interval : 0.000128 Sampling Parameter Resolution : 0.000128 Sampling Parameter Unit : SECOND Section 'RAD' ============ Total Fovs : 1 Data Rate : 1.300000 'RAD' Detectors --------------- PVORADANT 'RAD' Electronics ----------------- PVORADCTL In modes -------- HAA IM1 IM2 'RAD' Section FOV Shape 'ELLIPSOIDAL' ------------------------------------- Section Id : RAD Fovs : 1 Horizontal Pixel Fov : 29.000000 Vertical Pixel Fov : 25.000000 Horizontal Fov : 29.000000 Vertical Fov : 25.000000 'RAD' Section Parameter 'RADIANCE' ---------------------------------- Radiance is the amount of energy per time per projected area per steradian. Instrument Parameter Name : RADIANCE Sampling Parameter Name : TIME Instrument Parameter Unit : WATTS/AREA/STERADIANS Minimum Instrument Parameter : 0.010000 Maximum Instrument Parameter : 10.230000 Noise Level : 0.050000 Sampling Parameter Interval : 12.000000 Sampling Parameter Unit : SECOND Instrument Detector 'PVORADANT' =============================== Detector Type : ANTENNA Detector Aspect Ratio : 1.000000 Minimum Wavelength : 170000.000000 Maximum Wavelength : 170000.000000 Nominal Operating Temperature : 298.000000 Description ----------- Transmitter and receiver use the same detector: a 13 cm linearly polarized short-backfire antenna. The 3dB one-way beamwidth is 29 degrees in the E-plane and 25 degrees in the H plane. In normal operation, the E-field is tangent to the Venus surface and the H-field is normal to the Venus surface. The antenna is mounted on the periphery of the instrument bay, at an azimuth of 45 degrees relative to the spacecraft X-axis. It is articulated in one direction and moves under control of a stepping motor commanded by the radar command processor. Sensitivity ----------- Measured antenna gain was 17 dB. The first sidelobe was 16 dB less than peak, and the sidelobe level at 90 degrees was 29 dB relative to peak. 3dB beamwidth was 29 degrees for the E-plane and 25 degrees for the H-plane. Instrument Electronics 'PVORADCTL' ================================== Description ----------- The radar electronics consisted of a series of closely coupled sub-units: (a) RF sub-system, consisting of receiver, transmitter, up- and down-converters, and digital frequency synthesizer, (b) Synchronizer sub-system, containing a command processor, ephemeris generator to calculate the range-gate settings, timing circuits, and electronics to control the antenna stepping motor, (c) Radar Processor sub-system, that detects, samples, and formats the echoes, and (d) Power Supply sub-system. Instrument Mode 'HAA' ===================== Data Path Type : REALTIME Instrument Power Consumption : 30.000000 In sections ----------- ALT RAD Description ----------- High-altitude altimetry mode. Above 700 km altitude, the altimeter is making a single range measurement per 12 second spacecraft rotation period. Instrument Mode 'HAA' ===================== Data Path Type : REALTIME Instrument Power Consumption : 30.000000 In sections ----------- ALT RAD Description ----------- High-altitude altimetry mode. Above 700 km altitude, the altimeter is making a single range measurement per 12 second spacecraft rotation period. Instrument Mode 'IM1' ===================== Data Path Type : REALTIME Instrument Power Consumption : 30.000000 In sections ----------- ALT IMG RAD Description ----------- Altimetry and single-sided imaging mode. Below 700 km altitude, the altimeter is making 4 range measurements, and the SAR is making a map on one side, for each 12 second spacecraft rotation period. Instrument Mode 'IM1' ===================== Data Path Type : REALTIME Instrument Power Consumption : 30.000000 In sections ----------- ALT IMG RAD Description ----------- Altimetry and single-sided imaging mode. Below 700 km altitude, the altimeter is making 4 range measurements, and the SAR is making a map on one side, for each 12 second spacecraft rotation period. Instrument Mode 'IM2' ===================== Data Path Type : REALTIME Instrument Power Consumption : 30.000000 In sections ----------- ALT IMG RAD Instrument Mode 'IM2' ===================== Data Path Type : REALTIME Instrument Power Consumption : 30.000000 In sections ----------- ALT IMG RAD Mounted On Platform 'PIONEER VENUS ORBITER' =========================================== Description ----------- Please see Spacecraft Description.