The effect of steep sea-waves on polarization ratio at low grazing angles

A backscattering numerical model based on a two-scale representation of sur face roughness is developed for one-dimensional (1-D) sea surfaces at low g razing angles. The effect of the large-scale roughness component is account ed for by a numerical solution of the integral equation for surface field o btained in the forward-scattering approximation. The presence of the small- scale roughness responsible for backscattering is treated by the small-pert urbation theory. The numerical simulations accomplished support the viewpoi nt that the significant difference between experimentally observed and nume rically calculated values of polarization ratio for low grazing angles is m ost likely due to inadequate modeling of surface roughness. It is demonstra ted that adding a few relatively minor steep-wave-like features to the surf ace with the standard Pierson-Moskowitz spectrum will change the average po larization ratio dramatically, bringing its theoretical values from about - 20 dB to experimentally observed values of a few negative dB, Half of this increase is due to steepening of the front faces of the undulating waves. H owever, the other 10 dB of increase is due to diffraction effects, which en hance the scattering coefficient for the HH-polarization on the front faces of the steep waves.