MULTIPATH EM SCATTERING FROM BREAKING OCEAN WAVES AT GRAZING-INCIDENCE

The electromagnetic scattering from a breaking water wave with near gr azing illumination has been examined using both experimental measureme nt and numerical calculation. The scattering from a metal model of a b reaking wave of 1.2 m wavelength was characterized at grazing angles r anging from 0 degrees to 25 degrees and at frequencies ranging from 6 GHz to 12 GHz. Strong multipath interference is observed in the vertic al polarization (VV) backscatter and much weaker interference is seen in the horizontal polarization (HH) backscatter. Scattering from the w ave profile both with and without the breaking plume shows that the pl ume is the dominant scattering feature. Numerical calculation of the s cattering from modified surface profiles shows that the interference i s due to multipath scattering from the plume and front face of the wav e. HH interference is substantially smaller than that of VV because th e scatter from the plume in the multipath direction (toward the front face) is greatly reduced owing to the conducting surface boundary cond itions. The relative levels of the plume and expected distributed-surf ace scattering are consistent with the wave-tank measurement of horizo ntally polarized sea spikes from breaking waves of this scale.