The emissivity of foam-covered water surface at L-band: Theoretical modeling and experimental results from the frog 2003 field experiment
Sea surface salinity can be measured by microwave radiometry at L-band (1400-1427 MHz). This frequency is a compromise between sensitivity to the salinity, small atmospheric perturbation, and reasonable pixel resolution. The description of the ocean emission depends on two main factors: 1) the sea water permittivity, which is a function of salinity, temperature, and frequency, and 2) the sea surface state, which depends on the wind-induced wave spectrum, swell, and rain-induced roughness spectrum, and by the foam coverage and its emissivity. This study presents a simplified two-layer emission model for foam-covered water and the results of a controlled experiment to measure the foam emissivity as a function of salinity, foam thickness, incidence angle, and polarization. Experimental results are presented, and then compared to the two-layer foam emission model with the measured foam parameters used as input model parameters. At 37 psu salt water the foam-induced emissivity increase is -0.007 per millimeter of foam thickness (extrapolated to nadir), increasing with increasing incidence angles at vertical polarization, and decreasing with increasing incidence angles at horizontal polarization.
Camps A, Vall-Ilossera M, Villarino R, Reul Nicolas, Chapron Bertrand, Corbella I, Duffo N, Torres F, Miranda JJ, Sabia R, Monerris A, Rodriguez R (2005). The emissivity of foam-covered water surface at L-band: Theoretical modeling and experimental results from the frog 2003 field experiment. Ieee Transactions On Geoscience And Remote Sensing. 43 (5). 925-937. https://doi.org/10.1109/TGRS.2004.839651, https://archimer.ifremer.fr/doc/00000/10940/