Polarimetric radar imagery of the ocean at low grazing angles under atmospheric conditions of variable stability

Radar has been used from airborne and space platforms to monitor ocean surface effects, e.g., ocean surface and internal waves, currents, and pollution (oil patches). Polarimetric imaging radar is an emerging tool for remote sensing of the oceanic surface because different polarizations are sensitive to different surface phenomena. Polarimetric radar images of ocean areas obtained at low grazing angles with a Russian airborne real-aperture K_u-band radar at New York Bight in July 1992 were analyzed. A negative temperature gradient existed in the atmospheric surface layer, causing convective motions that control the distribution of echo spikes at each polarization. The most unusual aspect of low grazing angle radar imagery at K-, and X-bands wavelengths is the extreme sensitivity of the VV-polarization imagery to the atmospheric stability. Air-sea flux variability on horizontal scales from 100 m to several km results from the presence of coherent convective structures within the atmospheric boundary layer. The horizontal distribution of fluxes within these convective vertical motions is central to studies of air-sea interaction and remote sensing of sea surface wind and wave fields.