|Instrument: SASS : SEASAT-A Scatterometer System|
Earth Remote Sensing Instruments
Instrument Class: Active Remote Sensing
Instrument Type: Scatterometers
Related Data Sets
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A scatterometer provides the backscatter cross-section as a function of
incidence angle for the area under observation. In the case of the SASS, the
main interest was in measuring the ocean surface backscatter as a means to
derive the surface wind vector. The physical basis for this technique is that
the strength of the radar backscatter is proportional to the amplitude of the
surface capillary waves (Bragg scattering), which in turn is related the wind
speed near the surface. Moreover, the radar backscatter is anisotropic,
allowing the wind direction to be derived from backscatter measurements at
different azimuth angles. In practice, however, there was normally a fourfold
ambiguity in the wind direction that had to be resolved manually.
The SASS operated at a frequency of 14.6 GHz (or 2.0 cm). It incorporated four
dual-polarized fan beam antennas, two radiating +/- 45 degrees forward and two,
+/- 45 degrees aft, which produced an X-shaped pattern of illumination on the
Global measurements of the surface wind velocity over the seas were obtained
from SASS at least once every 36 hours with the high latitudes being covered
more frequently. The resolution of the instrument was 50 km and the grid
spacing of the output data product, 100 km.
Elachi,C., 'Microwave and Infrared Satellite Remote Sensors,' in MANUAL OF
REMOTE SENSING, edited by R.N.Colwell, pp 571-650, American Society of
Photogrammetry, Sheridan Press, Falls Church, Virginia, 1983. ISBN 0-937294-41
Cornillon, P., A GUIDE TO ENVIRONMENTAL SATELLITE DATA, Graduate School of
Oceanography, U. Rhode Island, Technical Report 79, 1982.
Special Issue on the SEASAT-1 Sensors, IEEE JOURNAL OF OCEANIC ENGINEERING,
Vol. OE-5, No.2, 1980.
Additional information on the SEASAT-1 spacecraft and the sensor available at