In a recent paper, Ocampo-Torres and Robinson [1990] (hereinafter referred to as OR) attempt to demonstrate that the tilt modulation transfer function relating the modulation of microwave power backscattered from the sea to long ocean waves is a more significant source of modulation than had been previously suspected, especially for winds near the azimuthal direction. They argue that because of the sensitivity of the normalized radar cross section of the sea, sigma0, to facet tilting both in and normal to the plane of incidence, the tilt modulation transfer function is very sensitive to wind direction and may be quite large for winds in the azimuthal direction. Unfortunately, these conclusions result from the unrealistic short-wave variance spectrum chosen by OR. They assumed that no mean backscatter occurred in directions perpendicular to the wind and let the short-wave spectrum go to zero in that direction. Scatterometry clearly shows us that this is not the case. Below we will show that for a short-wave spectrum which has finite spectral density in the cross-wind direction, the tilt modulation transfer function depends little on wind direction.
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