Bistatic scattering from the sea surface at L-band

A bistatic electromagnetic wave scattering model for the sea surface is developed to examine its wind dependence property over a wide range of incident angles along the specular direction. This is done by combining an existing scattering model with a sea spectrum calibrated by altimeter measurements at 14 GHz. Generally, surface scattering is sensitive only to a portion of the surface correlation measured from the origin. The width of this portion is a function of three variables (the incident angle, the surface height standard deviation and the exploring wavelength) and the functional form of the correlation function. When the correlation function is very slowly decaying, this width may be significant even for surfaces with large surface standard deviations. It is worth noting that this latter property is characteristic of the sea surface and this is the reason why surface scattering model based on geometric optics is not generally applicable to sea surface scattering. For radar sensing of wind speed along the specular direction at L-band it appears that greater sensitivity occurs at larger incident angles. The HH scattering coefficient is much larger than VV as expected. For a wind speed range of 4 to 20 m/s the change in the scattering coefficient at 70 degrees is close to twice the change at normal incidence, Hence, we expect more accurate measurements of wind dependence at larger incident angles using horizontal polarization.