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A model has been developed for average radar backscatter from terrain based on recent carefully controlled wide-bandwidth measurements of vegetation, snow-covered ground, and sea ice and on a comparison with measurements over North America by the Skylab S-193 scatterometer. The models for the thiree cases take the form Â¿Â° dB = A + BÂ¿ + Cf+ DfÂ¿, 20Â° Â¿ angle of incidence Â¿ 70Â°, where the constants vary depending on polarization and terrain class. They also differ above and below a critical frequency (6 GHz for general terrain, 8 GHz for sea ice, and between 8 and 12 GHz for snow). For angles of incidence of 0Â° (vertical) and 10Â°, the model is of the form Â¿Â° dB = M(Â¿) + N(Â¿)f over the range 1 to 18 GHz. Hundreds of thousands of measurements contributed to the general (vegetated terrain) model, and smaller numbers contributed to the snow and sea ice models. Since 1974 all measurements have been made with University of Kansas microwave spectrometers. A brief discussion of fading shows that insufficient data are available to describe the ranges adequately.