The<tex>SASS^{1}</tex>scattering coefficient<tex>σ</tex>° algorithm

Abstract

This paper describes the algorithms used to convert engineering unit data obtained from the Seasat-A satellite scatterometer (SASS) to radar scattering coefficients ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma\deg</tex> ) and associated supporting parameters. A description is given of the instrument receiver and related processing used by the scatterometer to measure signal power backscattered from the earth's surface. The applicable radar equation used for determining <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma\deg</tex> is derived. Sample results of SASS data processed through current algorithm development facility (ADF) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma\deg</tex> algorithms are presented which include <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma\deg</tex> values for both water and land surfaces, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma\deg</tex> signatures for these two surface types are seen to have distinctly different characteristics. As expected, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma\deg</tex> values for water show strong dependence on both incidence angle and wind speed. For land, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma\deg</tex> values are relatively independent of incidence angle above <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20\deg</tex> and have values in the range <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-14 &lt; \sigma\deg &lt; -6</tex> dB. <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sigma\deg</tex> measurements of the Amazon rain forest indicate the usefulness of this type of data as a stable calibration reference target. Using this Amazon data, relative biases between all four antennas and both polarizations are shown to be less than 0.4 dB.