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The radar response from the Amazon rain forest has been studied to determine the suitability of this region for use as a standard target to calibrate spaceborne scatterometers. Backscattering observations made by the Seasat-1 scatterometer system (SASS) show the Amazon rain forest to be a homogeneous, azimuthally isotropic radar target which is insensitive to polarization. The variation with angle of incidence may be adequately modeled as σ ° (dB) = aθ + b. Typical values for the incidence-angle coefficient a are 0.07-0.15 dB/degree. No change in the relations was observed over the 99 days of the Seasat mission. A small diurnal effect occurs, with measurements at sunrise being 0.5-1 dB higher than the rest of the day. For a fixed incidence angle and time of day the standard deviations ranged from 0.6 dB at the extremes to 0.1 dB at the antenna pointing angle of 44°. Because of its consistent response the Amazon forest appears to be a suitable target for calibrating spaceborne scatterometers. Further research is needed to check for seasonal effects at other times of year.
Birrer et al. (Fri,) studied this question.