NASA Scatterometer (NSCAT)

Description

The NASA Scatterometer (NSCAT), an active microwave satellite scatterometer, was developed by NASA/JPL as part of the NASA's Earth Probe Mission To Planet Earth (MTPE) program and flown on the Japanese Advanced Earth Observation Satellite (ADEOS). The NSCAT instrument is intended to be a follow-on to the Seasat-1 scatterometer (SASS) flown in 1978. The NSCAT was designed to measure the ocean surface wind velocity and provided data on air-sea interactions, calculations for large-scale fluxes between atmosphere and ocean, air-sea coupling and interannual variability of the Earth's climate. The NSCAT was a 13.995 GHz (Ku-band) active microwave radar that transmitted continuous pulses to the ocean surface and received backscattered radiation from the Earth. The radar cross section of the surface was used to derive the backscattered radiation as a function of both wind speed and direction and to determine the wind vector. The NSCAT consisted of three major subsystems: the Radio Frequency Subsystem (RFS), the antenna subsystem, and the Digital Data Subsystem (DSS). Transmittted pulses at 13.995 GHz are generated by the RFS to each antenna beam. A low-noise amplifier of 3 dB was used to amplify the return echo. The antenna subsystem consisted of 6 identical, dual-polarization fan beam antennas, approximately 10 feet long. The six antennas were calibrated to 0.25 dB prior to launch. The NSCAT was the first spaceborne scatterometer to employ on-board digital processing of the Doppler-shifted signal. The NSCAT measured two swaths, each 600 km wide at nadir and radar cross sections in three azimuth angles for a wind speed accuracy of 2 meter/sec and direction accuracy of 20 degrees and a spatial resolution of 25 km. NSCAT data was processed to science products directly from telemetry by the NSCAT Data Processing and Instrument Operations (DP&IO). See Naderi, F.N., et al. 1991: "Spaceborne Radar Measurement of Wind Velocity Over the Ocean - An Overview of the NSCAT Scatterometer System", Proceedings IEEE, Vol. 79, pp. 850-866 (B39955).