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Instrument: NSCAT : NASA Scatterometer
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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 will be 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 is designed to measure the ocean
surface wind velocity and will provide 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
transmits continuous pulses to the ocean surface and will receive
backscattered radiation from the Earth. The radar cross section of the
surface is used to derive the backscattered radiation as a function of
both wind speed and direction and to determine the wind vector. The
NSCAT consists 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
will be the first spaceborne scatterometer to employ on-board digital
processing of the Doppler-shifted signal. The NSCAT measures 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
is 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). For more information see: