ON THE THEORY OF ELECTROMAGNETIC-WAVES SCATTERING FROM THE SEA-SURFACE AT LOW GRAZING ANGLES

Scattering of electromagnetic (EM) waves from the sea surface is usual ly considered with the help of a two-scale (composite surface) model. It is shown theoretically that for broad wavelength range at grazing a ngles less than about 20 degrees, diffraction of the incident field on large-scale (undulating) components cannot be considered using the ta ngent plane (Kirchhoff) approximation. In other words, an undulating s urface cannot be treated as a set of locally plane facets, and its cur vature becomes an important parameter. The effects of curvature of the undulating surface are estimated for a two-dimensional situation. It is shown that in this case, backscattering cross sections at low grazi ng angles are proportional to the sin(2) alpha rather than to the sin( 4) alpha (which would be the case according to Rice's classical formul ae). This corresponds to experimental results. The theoretical curve o f the sigma(HH)/sigma(VV) ratio fits well the experimental data publis hed by Lee et nl. [1995] (for ''slow'' signals).