Abstract
With the increase of sea surface wind speed, whitecaps will appear on the sea surface. Generally, for Electromagnetic (EM) scattering of the foam-covered sea surface, medium-scale waves are used to replace the breaking waves of the real sea surface. Another treatment in computation is to adopt one of the whitecap coverages and fixed foam layer thickness. In fact, the evolution process of a breaking wave goes through two stages: stage A (crest foam) and stage B (static foam). In this paper, a geometric model of the sea surface covered with crest foam and static foam is established. The coverage ratio of stage A and stage B is proposed for the first time for a given sea state. In addition, different foam layer thickness distributions in each foam for various wind speeds are also considered. Based on the facet scattering theory of sea surface, this paper adopts the modified facet-based scattering model to deal with the scattering contribution of the sea surface and the effect of foam. Finally, in order to verify the accuracy of the geometric modeling and the scattering model of the sea surface, the EM backscattering of sea surface under different sea states are calculated. Simulation results show that the results of the proposed model are more consistent with the measured data than the results of the sea surface covered with individual crest foam or the sea surface covered with individual static foam.
Highlights
In the research field of Electromagnetic (EM) scattering of the sea surface, the EM mechanism of radar echo under high sea conditions and large incident angles has attracted lots of attention
When the wind speed reaches 7 m/s, the sea surface is beginning to froth, while more than 30% of the sea surface area is covered with foam as the wind speed reaches 25 m/s [1]
Anguelova and Gaiser [7] analyzed the physical parameters of the foam layer on the sea surface
Summary
In the research field of Electromagnetic (EM) scattering of the sea surface, the EM mechanism of radar echo under high sea conditions and large incident angles has attracted lots of attention. Kudryavtsev et al [13,14] established a semi-empirical model to modify the scattering coefficient of the sea surface by considering the breaking wave and whitecap coverage. A 3-D scattering model of sea surface covered with crest foam and static foam is proposed. The main idea is to find out the geometric modeling of real sea states and the coverage proportion of crest foam and static foam in a given sea state. In order to verify the correctness and the effectiveness of the proposed model, the numerical results of the EM backscattering coefficient are simulated in some cases for different wind speeds, incident angles, operation frequencies and wave polarizations. Some discussions and conclusions are presented in the final section
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