Relationship between wind vectors and L-band radar cross sections examined using PALSAR

The relationship between ocean wind vectors and L-band normalized radar cross sections (NRCS) is examined using the Phased-Array L-band Synthetic Aperture Radar (PALSAR). We used PALSAR ScanSAR images with a wide range of incidence angles from 17deg to 43deg. More than 6,000 match-ups, each consisting of the NRCS, incidence angles, wind speeds and wind directions, were collected. The NRCS exhibits a power-law relationship with respect to the wind speed. The coefficients of the power law can be derived as a function of the incidence angles. Based on this relation, the wind speeds are then inversely estimated from the NRCS and the incidence angles. A comparison with the truth winds reveals -0.23 m/s bias and 2.63 m/s rms error, demonstrating the feasibility of L-band scatterometry. Collecting more match-ups and further considering wind- direction dependence, which was not included in this study, would lead to the derivation of a robust L-band model function.