Wind‐wave modeling and the scattering problem.

Wind‐wave modeling appears to be the weakest link in the surface‐scattering modeling problem. Wave models are based mainly on early ocean measurements at very low frequencies, which showed strong dispersion effects and frequency spectra with F−5 asymptotes for fully developed sea conditions. Analysis indicated that this is consistent with irrotational wave theory, wherein first‐order nonlinear interactions are negligible. Flume measurements at higher frequencies and shorter fetch, on the other hand, show dispersionless propagation and spectra with F−3 asymptotes. Analysis shows that this is consistent with the observed asymmetric steepening of wave fronts, which appears to be due to combined effects of dispersion and first‐order nonlinearity. The proposed mechanism for first‐order nonlinear interactions is vortical wave motion induced by wind stress. Azimuthal dependence of scattering strength associated with waveform asymmetry/skewness has already been observed in microwave radar experiments.