Normalized radar cross sections and modulation transfer functions (MTFs) for microwave backscattering from the sea surface have been measured at both L- and Ku-Bands during the Tower Ocean Wave and Radar Dependence Experiment. Long waves during the experiment were usually not generated by the local wind, so a unique opportunity was afforded to investigate the effects of arbitrary wind, wave, and antenna angles on the backscatter. Data were collected using horizontal polarization at L-Band and vertical polarization at Ku- Band. Cross sections at L-Band are shown to be isotropic with respect to wind-antenna anlge and nearly independent of wind speed except at the lowest wind speeds. Ku-Band cross sections, on the other hand, show the expected wind-antenna angle anisotropy and wind speed dependence. The Ku-Band cross sections agree well in magnitude with previous wave-tank and satellite measurements, casting doubt on the dependence of cross section on antenna height which has been suggested in the literature. At both frequencies the data suggest that cross sections may be lowered slightly when long waves propagate at large angles to the wind. Consistent with the cross section results, MTFs at L-Band are shown to depend little on wind speed, while those at Ku-Band decrease with wind speed. The results agree with previous studies. At both frequencies, MTFs depend little on wind-antenna angle for a constant wave-antenna angle. On the other hand, for a constant wind-antenna angle, MTFs decrease with increasing wave-antenna angle. Implications of these results for radar imagery of the sea surface and for the theoretical interpretation of the origin of MTFs are discussed.
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