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Electromagnetic simulation and time-frequency analysis of sea clutter

Sea clutter is the backscattered returns from a patch of the sea surface illuminated by a radar pulse. An efficient computational electromagnetic (CEM) method based on ray tracing algorithm and a time-frequency analysis method are applied to simulate and analyze the sea clutter from wind-driven sea surface and breaking waves. First, the three dimensional (3-D) time-evolving sea surface is geometrically modeled based to the wind-driven spectrum and breaking waves. The combination of geometrically modeling wind-driven sea surface and breaking waves is the novelty of the work in this paper. It is fundamental for the electromagnetic simulation and analysis of sea clutter. Second, the electromagnetic (EM) backscattering is calculated by using the ray tracing method. This kind of CEM method can compute the EM scattering from large dynamic complex sea surfaces at different polarizations and different incident angles in both time and frequency domains. Last, with the help of quasi-static approach, the time-evolving sea echoes are acquired by massive simulations of static sea surface, then the Doppler spectra are computed for the combined sea surface by the short time Fourier transform. The sea clutter contains a low value power and from the Doppler spectrum, it is reasonably well modeled by tilt-modulated Bragg scattering. Moreover, some spiking events which is associated with breaking waves occur and have a high power and velocity. The research results of this paper can be applied in the electromagnetic simulation of the sea surface, the inversion for the sea surface parameters and the detection of the targets on the sea surface.