LOW-GRAZING SCATTERING FROM BREAKING WATER-WAVES USING AN IMPEDANCE BOUNDARY MM GTD APPROACH/

The radar backscattering from water waves of various degrees of breaki ng is numerically examined, A hybrid moment method geometrical theory of diffraction (MM/GTD) technique previously used for small-grazing sc attering from perfectly conducting surfaces is reformulated using impe dance boundary conditions, allowing the treatment of large (but finite ) conductivity scattering media such as sea water. This hybrid MM/GTD approach avoids the artificial edge effects that limit the standard mo ment method when applied to rough surfaces, allowing the calculation o f the scattering at arbitrarily small grazing angles, Sample surfaces are obtained through the edge detection of video stills of breaking wa ves generated in a wave tank, The numerical calculations show that the strength of the backscatter is closely associated with the size of th e plume on the breaking wave, Strong interference appears in the both horizontal (HH) and vertical (VV) backscatter when the surfaces are tr eated as perfectly conducting, The VV interference is dramatically red uced when a sea water surface is used, but the HH interference is unaf fected. The interference leads to HH/VV ratios of up to 10 dB, The beh avior of the scattering is consistent with the multipath theory of sea -spike scattering.