RADAR SEA RETURN IN HIGH SEA STATES
NAVAL RESEARCH LAB WASHINGTON DC
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In order to obtain a more exact specification of the variation of the radar cross section of the sea with increasing sea roughness, and to determine a worst-case condition for sea clutter, a high-sea-state clutter measurement program in the North Atlantic was conducted. Radar return was collected on four frequencies in both linear and cross polarizations, and the normalized radar section sigma sub o of the sea surface was obtained as a function of radar and surface parameters for the high sea states encountered. The study of the behavior of the median value of sigma sub o as a function of the radar parameters and sea conditions resulted in the following conclusions at high sea states characterized by winds of 20-50 knots and wave heights of 10-26 ft a the value of sigma sub o is independent of wavelength for vertical polarization but maintains an inverse wavelength dependence for horizontal polarization, b the direct polarization ratio remains significant for all wavelengths as the sea roughness increases and is a function of wavelength, c the value of sigma sub o is sensitive to wind direction, with consistently higher clutter observed in the upwind direction for all wavelengths and both direct polarizations, and d the value of sigma sub o does not increase significantly with wind velocity in the region 20-50 knots, indicating that sigma sub o approaches a maximum value, or saturation, with increasing surface roughness.
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