Ku-band Polarization Difference Model for the Scatterometer Wind Inversion

The CFOSAT mission provides a unique data set of collocated nadir, near-nadir and moderate angle dual-polarization Ku-band radar measurements. These combined measurements open new opportunities to revisit existing interpretation and approaches to analyze ocean radar backscatter signals. In particular, actual scatterometer wind vector retrieval algorithms and definitions of Geophysical Modulation Functions (GMFs) can be revisited, including sensitivity to additional parameters: wave state, currents, etc. The present work describes an alternative GMF approach based on the analysis of signal polarization differences, and interpretation in terms of ocean surface wind-roughness spectra. Based on CFOSAT measurements, the polarization-difference GMF reproduces main properties of standard empirical radar GMFs. However, it is more directly related to a theoretical short wave spectral model. This approach naturally enables the inclusion of additional sea state variables. Results of this work is intended to be implemented in wind retrieval processors to complement existing methods.