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 usually considered with the help of a two-scale (composite surface) model. It is shown theoretically that for broad wavelength range at grazing angles less than about 20°, diffraction of the incident field on large-scale (undulating) components cannot be considered using the tangent plane (Kirchhoff) approximation. In other worlds, an undulating surface cannot be treated as a set of locally plane facets, and its curvature becomes an important parameter. The effects of curvature of the undulating surface are estimated for a two-dimensional situation. It is shown that this case, backscattering cross sections at low grazing angles are proportional to the sin2α rather than to the sin4α (which would be the case according to Rice's classical formulae). This corresponds to experimental results. The theoretical curve of the σHH/σVV ratio fits well the experimental data published by Lee et al. [1995] (for ″slow″ signals).