Retrieval of gravity-capillary spectrum parameters by means of microwave radiometric techniques

The paper presents some results obtained during a series of microwave remote sensing experiments carried out on the Black Sea coast in 1999-2002. The measurements were made from a pier at the South Department of the Shirshov Institute of Oceanology with microwave radiometers operating at wavelengths of 1.5, 0.8, 0.5, and 0.3 cm. The surface wave spectrum parameters were estimated from angular radiometric measurements using a novel approach. Microwave brightness contrasts at Ka-band (37 GHz) measured over wide range of incidence angles were used for a curvature spectrum of gravity-capillary waves and a mean-square slope of gravity waves retrieval. The evolution of spectrum parameters under variable wind (ranged from 0.5-7 m/s) was investigated. The delay of brightness variation relative to wind speed as large as 1-2 h was found. The performed spectral analysis permitted to relate the observed brightness delay to short gravity-capillary surface waves, whereas longer gravity waves followed the wind practically without any delay. It is concluded that the proposed technique of gravity-capillary wave spectrum retrieval provides a useful tool for investigation of air-sea interaction and surface wave dynamics.