Radar imaging of the ocean surface |
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| Authors: | Charles Elachi |
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| Institution: | (1) Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California, USA |
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| Abstract: | Radar sensors are being used to provide two-dimensional imagery of the ocean surface. The radar image has a brightness variation which is proportional to the local backscatter cross-section of the surface at the wavelength of observation. The backscatter cross-section is, in turn, a function of the local surface topography and, in the case of a coherent radar system, of the surface dynamics. The synthetic-aperture radar imaging technique produces very high resolution images essentially independent of the distance to the surface being imaged. This technique is discussed in some detail. The emphasis is on recent observations of a large variety of ocean surface patterns. Deep ocean waves have been observed under a variety of weather conditions, including hurricanes. Breaking waves are observed because of the increase in roughness and the presence of foam. Discrete wave-like patterns, which resemble internal wave trains, have been observed in numerous locations; and eddy-shaped, linear, curvilinear and periodic slicks have also been seen. The different models for wave image formations are briefly reviewed. Specifically, the roughness modulation, tilt modulation, and orbital velocity models are discussed. Finally, it is shown that surface randomness does not destroy the coherence of the signal needed to generate the synthetic-aperture image because of the short-term coherence of the small Bragg waves.This paper presents the result of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract NAS7-100, sponsored by the National Aeronautics and Space Administration. |
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