The emissivity of foam-covered water surface at L-band: theoretical modeling and experimental results from the FROG 2003 field experiment

摘要

Sea surface salinity can be measured by microwave\udradiometry at L-band (1400–1427 MHz). This frequency is a\udcompromise between sensitivity to the salinity, small atmospheric\udperturbation, and reasonable pixel resolution. The description\udof the ocean emission depends on two main factors: 1) the sea\udwater permittivity, which is a function of salinity, temperature,\udand frequency, and 2) the sea surface state, which depends on the\udwind-induced wave spectrum, swell, and rain-induced roughness\udspectrum, and by the foam coverage and its emissivity. This study\udpresents a simplified two-layer emission model for foam-covered\udwater and the results of a controlled experiment to measure the\udfoam emissivity as a function of salinity, foam thickness, incidence\udangle, and polarization. Experimental results are presented, and\udthen compared to the two-layer foam emission model with the\udmeasured foam parameters used as input model parameters. At\ud37 psu salt water the foam-induced emissivity increase is 0.007\udper millimeter of foam thickness (extrapolated to nadir), increasing\udwith increasing incidence angles at vertical polarization,\udand decreasing with