Scattering from rough water surfaces using an impedance-boundary periodic-surface moment method

A periodic-surface implementation of the the moment method has been extended to allow the calculation of electromagnetic scattering from rough dielectric interfaces to arbitrarily large incidence angles (small grazing angles). Impedance boundary conditions are used to treat large but finite conductivity scattering media. The technique has been used to find the 30 GHz scattering from surface profiles derived from direct measurements of the upwind/downwind slopes of wind-roughened water surfaces generated in a wave tank. The calculations show that a significant asymmetry (5 dB) appears between the upwind and downwind looking scattering at incidence angles above about 50/spl deg/ when the surface profiles show distinct bound capillary wave energy. The two-scale scattering model proved able to accurately predict the asymmetry at horizontal polarization at incidence angles up to about 75/spl deg/ but did not predict any asymmetry at vertical polarization. The two-scale model loses accuracy above 75/spl deg/ at horizontal polarization but accurately predicts the upwind looking vertically polarized scattering at up to 89/spl deg/.