Numerical Investigation of Radar Scattering from the Sea Surface at Small Grazing Angles

The scattering from measured and modeled sample one-dimensionally rough water surfaces is being calculated using two distinct extensions of the standard moment method (MM) that allow application at arbitrarily small scattering angles. The first method is a hybrid approach that extends the moment method using the geometrical theory of diffraction (GTD). The front and back faces of the surface are extended to infinity, eliminating the need for an illumination weighting function that limits the efficiency of standard MM when applied to rough surfaces at small grazing angles. Single basis functions derived from GTD are used to describe the current on the infinitely extending surfaces, limiting the computational expense of the approach. The other extended MM approach treats the surface as periodic, again giving an infinitely extending surface that eliminates the need for an illumination weighting function. Finite conductivity water surfaces are treated using impedance boundary conditions. Iterative solution of the linear system resulting from the moment method is being used to allow larger surfaces to be treated.