Wind retrieval with cross-polarized SAR returns

Presently, wind velocity retrieval uses co-polarized (co-pol) normalized radar cross sections (NRCS) from the ocean surface (σοyy and σ0HH, respectively vertical transmit vertical receive and horizontal transmit horizontal receive). In recent analyses of the RADARSAT-2 (R2) quad polarization (quad-pol) data, it is found that whereas the co-pol backscatter shows a saturation trend in winds exceeding about 16 m/s for incidence angle 6*<;35°, the cross-polarized (cross-pol) backscatter continues to increase toward the highest wind speed. More importantly, the rate of increase of σ0VH with wind speed increases to about cubic in high winds (>;~10 m/s) from about linear in moderate winds (<;~7 m/s). Thus, the retrieved wind speed using σ0VH becomes more accurate in higher wind speeds. This is a significant breakthrough for monitoring hazardous wind events such as hurricanes and subtropical storms with wind speeds frequently exceed the ambiguity thresholds of wind retrieval using the co-pol radar backscatter. The spatial coverage of R2 quad-pol data is nominally 25 km by 25 km. For a large area of coverage, the Scan SAR beam modes (300 km for narrow and 500 km for widemode) are more practical, and the cross-pol data are only available in dual-polarization (dual-pol) mode, either HH and HV or VV and VH. Here the result of wind speed retrieval using dual-pol σ0VH is presented.