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Models for Electromagnetic Scattering from the Sea at Extremely Low Grazing Angles

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Memorandum rept.

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The present state of understanding in the field of low-grazing-angle sea scatter is reviewed and extended. The important concept of shadowing is approached from the point of view of diffraction theory, and limits in wind speed and radar frequency are found for the application of shadowing theories based on geometrical optics. The implications of shadowing function based on illumination thresholding are shown to compare favorably with a variety of experimental results. Scattering from the exposed surface peaks is treated by a composite-surface Bragg model, and by wedge models using both physical optics an the method of equivalent currents. Curiously, the scattering levels predicted by these widely different approximations are all in fairly good agreement with experimental values for moderately low grazing angles about 5 deg, with the physical optics wedge model being superior at 1 deg. A new scattering feature, the slosh, is introduced, with scattering behavior that resembles the temporal and polarization dependence of observed low angle returns from calm water. The plume model of scattering from breaking waves from earlier work is discussed as a source of high-intensity Sea Spikes. It is emphasized that the prediction of low angle scattering from the sea will require considerably more information about the shape, size, and distribution of the actual scattering features. Keywords Radar clutter, Rough surface, Backscattering, Sea clutter, Diffraction theory, Bragg scattering.

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  • Meteorology
  • Physical and Dynamic Oceanography
  • Active and Passive Radar Detection and Equipment

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