Future Ocean Scatterometry: On the Use of Cross-Polar Scattering to Observe Very High Winds

This paper investigates the potential of cross polarization (VH) to extend the upper dynamic range of the wind measurements from ocean scatterometry. An analytical model for the VH polar scattering of the microwave radiation from ocean is proposed. The model combines the second-order small-slope approximation theory with the vector radiative transfer theory to obtain a statistical expression of the ocean scattering in presence of foam. Cross-polarized backscatter signals from RADARSAT-2 C-band synthetic aperture radar imagery, which were acquired during severe weather events, and collocated/time-coincident stepped-frequency microwave radiometer wind measurements by the National Oceanic and Atmospheric Administration's hurricane-hunter aircraft are used to verify the model. The validity of the model has been also proven against European Centre for Medium-Range Weather Forecasts forecasted winds. The results suggest that the present scattering model can be a valuable tool for understanding VH at very high wind speeds and for interpreting the data collected by the future dual polarimetric wind scatterometer (SCA), which will be flown on the Second Generation Meteorological Operational satellite program (MetOp-SG) as an evolution of the Advanced Scatterometer instrument on board MetOp.