Search

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. Index Terms--Sea surface electromagnetic scattering.

A number of datasets from wave tank and field measurements have been assembled from published data. For fixed wind speed, the peak frequency has F ∝ x − 1 / 3 and the significant wave height has H ∝ x 1 / 2 . It has been confirmed following earlier work that wind speed should not be used to non-dimensionalise wave parameters, such as the frequency or the significant wave height because the wind-speed dependence is stronger than expected for the assembled data sets. New parameters have recently been proposed that use fetch, x, and the number of waves to create non-dimensional wave height and wave period, H ~ and T ~ . The applicability of these quantities to the assembled datasets has also been investigated. A new non-dimensional relationship has been found empirically that relates the wave steepness, ak to the dimensionless fetch, ν, of the waves, (a k) 2 ν = 130 (or H 2 k 3 x = 260), which has the property of being wind-speed invariant. The estimated wind-speed dependence varied with fetch, although the ratio between the wind-speed exponents for H and F remained constant at − 1 / 3 for all fetches. [ABSTRACT FROM AUTHOR]