Rough-sea microwave emissivities measured with the SSM/I

The combination of sea surface roughness and whitewater causes a change in emissivity from an undisturbed sea surface. Previous measurements of this effect have covered the frequency range 1-37 GHz. The seven-channel SSM/I (Special Sensor Microwave/Imager) on the Block 5D-2 spacecraft extends this range to 85.5 GHz, at a fixed viewing angle of 53° from normal. To correct for atmospheric attenuation, vapor and liquid water in the atmosphere and surface wind speed were simultaneously estimated from the 22.2 GHz vertically polarized and the 37.0 GHz dual-polarized channels. Data with liquid water burden in excess of 0.07 kg/m² were excluded. In the horizontally polarized measurements, the wind-speed sensitivity of emissivity at 85.5 GHz was greater than at 37.0 GHz by a factor of approximately 1.4. For vertical polarization at 85.5 GHz, the sensitivity was much smaller than for horizontal polarization, and somewhat smaller than for vertical polarization at 37 GHz