urn:nasa:pds:context:instrument:pvo.orad 2.0 1.20.0.0 Product_Context 2020-08-26 1.0 extracted metadata from PDS3 catalog and modified to comply with PDS4 Information Model 2024-04-02 2.0 Updated to IM 1.20.0.0 urn:nasa:pds:context:instrument_host:spacecraft.pvo instrument_to_instrument_host 10.1109/TGRS.1980.350255 Pettengill, G. H., et al., Pioneer Venus Orbiter radar mapper--design and operation, IEEE Trans. Geosci. Rem. Sens., GE-18, 28-32, Jan. 1980. reference.PETTENGILLETAT1980 10.1126/science.203.4382.806 Pettengill, G. H., et al., Pioneer Venus radar mapper experiment, Science, 203, No. 4382, 806-808, Feb. 1979. reference.PETTENGILLETAT1979a 10.1126/science.205.4401.90 Pettengill, G. H., et al., Venus: Preliminary topographic and surface imaging results from the Pioneer Orbiter, Science, 205, No. 4401, 91-93, doi:, July 1979. reference.PETTENGILLETAT1979b 10.1029/JA085iA13p08232 Masursky, H., et al., Pioneer Venus radar results: Geology from images and altimetry, J. Geophys. Res., 85, No. A13, 8232-8260, Dec. 1980. reference.MASURSKYETAT1980 10.1029/JB093iB12p14881 Pettengill, G. H., et al., Venus: Surface electromagnetic properties, J. Geophys. Res., 93, No. B12, 14881-14892, Dec. 1988. reference.PETTENGILLETAT1988 SURFACE RADAR MAPPER (ORAD) for PIONEER VENUS Radar not applicable not applicable INSTRUMENT OVERVIEW =================== The Pioneer Venus Orbiter radar altimeter (ORAD) was used to obtain information on the orbiter altitude, planetary surface temperature, and radar scattering properties in order to infer the surface topography, geology, and the thermal and mechanical properties of the interior of Venus. From observations of the radar echo, surface heights along the suborbital trajectory can be estimated to an accuracy of 150 m. Surface lectrical conductivity and meter-scale roughness can also be derived. The ORAD consists of a 38 cm diameter short backfire reflector antenna with a single axis positioning motor and an electronics box. The antenna is mounted on the periphery of the orbiter equipment shelf. The motor allows the antenna to be moved in a plane containing the spacecraft's spin axis. The antenna beams a low power (20 W peak pulse power), S-band (1.757 GHz), 30 degree beamwidth pulse to the surface, and the echoes are recieved and processed on-board. The instrument had a mass of 9.7 kg and used 18 W power. The measurements were made whenever the spacecraft was below 4700 km. The antenna is mechanically moved in a plane containing the spacecrafts spin axis to view the suborbital point on the planet's surface once during each roll of the spacecraft. Relatively long pulses are used to obtain a good signal-to-noise ratio from each pulse. The transmitted pulses are modulated, and the specifics of the pulse used depend on altitude. From periapsis to 700 km, a 55 baud (sub-pulse) code with a duration of 4 microseconds and a pulse repetition frequency (PRF) of 189.4 Hz is used. From 700 to 1515 km, the PRF is lowered to 92.8 Kz. From 1515 to 2575 km, a baud duration of 6 microseconds and a PRF of 108.2 Hz is used. From 2575 to 3000 the PRF is increased to 189.4 Hz. There were four types of measurements made by ORAD during each 12 second spacecraft revolution. Four along track altimetry measurements in four Doppler bands made below 700 km altitude. (Above 700 km there is one nadir measurement per spacecraft roll.) The radar observations occupy about 1 sec out of each 12 second spacecraft rotation period. A radiometric measurement (17 cm brightness temperature) was made with the antenna pointing towards nadir. One or two side looking imaging measurements were made with the antenna pointed to either side of the spacecraft nadir. A radiometer calibration measurement was made with the antenna pointing towards zenith (cold space). The surface resolution at periapsis is 23 km along track and 7 km across track. Each roll acquires 640 bits of data. The altimeter measurements were processed on board into profiles of echo power versus time delay. Each altimetry measurement yielded values of range, RMS surface slope, and Fresnel reflectivity. Each 12 second spacecraft revolution yielded one or two maps of radar backscatter, each resolved into 64 pixels. ORAD made measurements of the Venus surface from 5 December 1978 through 23 March 1981.