An empirical model of EM scattering from steepening wave profiles derived from numerical computations

The variation in scattered power from steepening wave profiles, as functions of radar frequency and bistatic grazing angles, has been investigated using a hydrodynamic code called CHY and a version of the forward-backward (FB) electromagnetic scattering code. A comparison of the frequency response of the FB numerical results with radar data showed excellent agreement and has indicated that the lateral coherence of a breaking wave is around one third of the water wavelength. A simple empirically derived model based on the height spectrum of the surface has been shown to capture almost all the important trends in the scattering, including the Doppler velocities, but with the exception of the effect of multipath. The Doppler spectrum of the steepening wave was found to be well modeled by a Lorentzian lineshape with different spectral widths for vertical-vertical and horizontal-horizontal polarization.