MULTI-ANGULAR MEASUREMENTS OF SEA-SURFACE POLARIZED MICROWAVE EMISSION CARRIED OUT DURING A SERIES OF GROUND-BASED EXPERIMENTS

Abstract

The results of sea-surface microwave brightness measurements carried out from a pier in 1999-2002 are presented. The measurements were performed by W-band microwave radiometer (wavelengths of 0.3 cm), and Ka-band radiometer-polarimeter (wavelength of 0.8 cm). All equipment was installed on a pier (200 meters long) at 3 meters over the surface; the sea depth at the site was approximately 8 meters. The microwave instruments were mounted on a rotating/scanning platform, which permitted measurements at angles from 10 up to 170 degrees off nadir over 300 degrees range of azimuthal angles. The measurements were carried out 24 hours a day under various meteorological conditions. Microwave brightness dependence on surface wind was studied over wide range of incidence angles. The modulus of brightness contrasts caused by the wind was shown to increase with wind speed increasing. Also, the brightness contrast at both polarizations changes its sign as the viewing angle increases. Under variable wind conditions, the delay of brightness variation relative to wind speed as large as 1-2 hours was found. This effect may be treated as an evidence of non-linear interaction of surface waves in coastal area