The emissivity of sea foam at 19 and 37 GHz

An airborne experiment was conducted over the Nantucket Shoals determine the emissivity of sea foam at 19 and 37 GHz, for vertical (V) and horizontal (H) polarizations. These frequencies represent those channels of the satellite-borne system Special Sensor Microwave Imager which are used to estimate the sea surface wind speed. Nine whitecaps were identified as providing 100% coverage for at least part of their signatures. The emissivities of these whitecaps were calculated on the basis of the peak brightness temperature recorded at 37 V, 37 H, and 19 V. The mean values of the emissivities at the respective frequencies and polarizations lie within 3% of the values predicted by the model of A. Stogryn (J. Geophys. Res., vol.77, p.658-1666, 1972). The 37-GHz emissivities vary by 25 to 30% of the mean while the 19-GHz values lies within 15% of the mean. The data are consistent with a single-parameter model depending on an effective foam fraction.>