Sea wave parameter obtained from airborne polarimetric observations during the Shoaling Waves'99 experiment

A microwave polarimetric radiometer offers the potential for measurement of the sea surface wind vector. This explains an increasing interest on the polarimetric observations of the ocean at various frequencies, viewing angles, and environmental conditions. The Environmental Technology Laboratory deployed a Ka-band cross-track scanning polarimeter on a Twin-Otter aircraft in the fall, 1999. The variation of brightness temperature as a function of viewing angle is sensitive to the gravity-capillary spectrum of sea surface waves and can be used to retrieve such a spectrum. A wide range of observation angles allowed the authors to measure the down-welling radiation from the atmosphere as well as the oceanic up-welling radiation. A high accuracy of the absolute measurement of the brightness temperature allowed the authors to determine the emissivity of the ocean surface. A retrieved spectrum of gravity-capillary waves is in reasonable agreement with model spectra.