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Radar Scatterometry and Altimetry 
Instrument status 
  
Radar scatterometers were developed when it was discovered that 
the return signal from radar altimeters was affected by the surface of 
the Earth. The S193 RADSCAT/Altimeter on Skylab, consisted of a radar 
scatterometer, a radar altimeter, and a passive microwave radiometer 
which operated at the same frequency, 13.9 GHz (2.16 cm) and time-shared 
a number of electronic components (Moore and Hooper, 1974). Plans call 
for a 14.5 GHz scatterometer and a 13.9 GHz compressed pulse altimeter 
for the Seasat-A mission. 
Scatterometers (0.4 and 13.3 GHz) for airborne testing have been 
flown on NASA Johnson Space Center multisensor aircraft. 
An 8-18 GHz radar spectrometer FM-CW system which transmits a 
triangular waveform and operates in 2 GHz steps, was designed and built 
at the University of Kansas Space Technology Laboratories to provide 
radar backscatter cross section (Bush and Ulaby, 1973). Radar cross 
section of vegetation canopies was measured by a 9 GHz, vertically 
polarized scatterometer in the Netherlands (Attema and others, 1974). 
The Dutch have used a short-range scatterometer to study oil slicks in 
a wave tank to get a better understanding of natural spills 
(Kuilenburg, 1975). 
Platform status 
  
Scatterometers are operated from the ground up to orbital altitudes. 
The Dutch bistatic scatterometer is truck mounted while the University of 
Kansas radar spectrometer is on a boom extendable to 26 m. Other 
Scatterometers and altimeters record from intermediate altitude and other 
aircraft, such as those of the NASA Johnson Space Center. The Skylab 
S193 system operated from 430 km and Seasat sensors are designed to 
operate from an orbital altitude of 800 km. 
Interpretation status 
The University of Kansas 8-18 GHz radar spectrometer collected about 
75,000 data points for determining scattering coefficients of selected 
agricultural targets and is being used to study moisture effects in soils. 
Skylab S193 system made measurements of the ocean under a number of 
different sea and wind conditions. 
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