Compact Polarimetry Synthetic Aperture Radar Ocean Wind Retrieval: Model Development and Validation

Abstract

We have developed C-band compact polarimetry geophysical model functions for RADARSAT Constellation Mission ocean surface wind speed retrieval. A total of 1594 RADARSAT-2 images acquired in quad-polarization SAR imaging mode were collocated with in situ buoy observations. This data set is first used to simulate compact polarimetric data and to examine their dependencies on radar incidence angle and wind vectors. We find that RR-pol radar backscatters are less sensitive to incidence angles and wind directions but are more dependent on wind speeds, compared to RH-, RV-, and RL-pol. Subsequently, the matchup data pairs are used to derive the coefficients of the transfer functions for the proposed compact polarimetric geophysical model functions, and to validate the associated wind speed retrieval accuracy. Statistical comparisons show that the retrieved wind speeds from CMODRH, CMODRV, CMODRL, CMODRR are in good agreement with buoy measurements, with root mean square errors of 1.38, 1.51, 1.47, 1.25 m/s, respectively. The results suggest that compact polarimetry is a good alternative to linear polarization for wind speed retrieval. CMODRR is more appropriate to retrieve high wind speeds than CMODRH, CMODRV or CMODRL.