Dual-frequency microwave backscatter from the ocean at low grazing angles: comparison with theory

Extensive experimental work has been performed in recent years involving the dual-frequency microwave scatterometer. This system can selectively measure the modulated return from a very narrow band of ocean wavenumbers. By varying the difference in transmitted frequencies a directional modulation spectrum may be obtained. Theories have been developed to explain the output of the dual-frequency spectrometer in quantitative terms. Because of the complexity of the measurements involved, these theories have, heretofore, only been partially tested. The experiments reported here independently evaluate both sides of a theoretical equation for χ(κ), the basic signal/background ratio for the technique, using single- and dual-frequency signals backscattered at low grazing angles. The experimental results agree well with the theoretical expression and provide evidence that composite surface theory is viable at quite low grazing angles.