A model for sea backscatter intermittency at extreme grazing angles

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Abstract
The behavior of microwave sea backscatter at extreme grazing angles (0°–1°) tends to be spiky and irregular, with ill‐defined statistics. Intuition suggests that at these extreme angles, most of the surface is in shadow, and only an occasional peak is visible to the radar. In order to sharpen this intuition, the conventional shadowing function is taken to define a scattering threshold whose height above the mean surface is a function of grazing angle and average surface slope. Using the spatial analogue of the familiar idea of “surges” and “fades” of a thresholded random process, the surface is found to be pockmarked by scattering islands of relatively constant size, but whose density (spacing−2) is a sensitive function of grazing angle and sea state. This model leads to the definition of a “backscatter intermittency index,” which describes the number of localized scattering regions within a given surface area as a function of wind speed and grazing angle, and to a modified shadowing function for grazing angles less than 1°.

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