New Geophysical Model Function for Ocean Emissivity at 89 GHz Over Arctic Waters

Abstract

New empirical geophysical model functions (GMFs) have been developed to interpret 89-GHz brightness temperature measurements over cold Arctic seas. Careful data screening is applied to the Advanced Microwave Scanning Radiometer 2 (AMSR2) multifrequency measurements to exclude atmospheric scattering and large absorption impacts, to estimate the 89-GHz sea surface emissivity and its relative changes with surface wind speed (SWS). Matched-up wind speeds are directly derived from the AMSR2 low-frequency measurements. The GMFs are obtained from the AMSR2 level 1R 89 GHz measurements corrected for the atmospheric impact with physical models and atmospheric parameters derived from the AMSR2 data. A carefully selected database encompasses mostly cold sea conditions (<4 °C) and a large range of wind speed conditions, including extratropical cyclone and polar low high-wind events over the Nordic Seas. Resulting GMFs contrast with previously proposed ones manifesting larger SWS signal at horizontal and positive SWS signal at vertical polarization.