Synergistic Measurements of Hurricane Wind Speeds and Directions from C-band Dual-Polarization Synthetic Aperture Radar

Abstract

Co- and cross-polarized geophysical model function (GMFs) both have limitations to retrieve ocean surface wind speeds. The former underestimates high winds and the latter overstimates low winds. In this study, we both use co- and cross-polarized SAR observations to retrieve hurricane wind speeds and directions. The local gradient method is first used to estimate hurricane wind directions from C-band RADARSAT-2 and Sentinel-1A dual-polarization SAR imagery. We compare wind directions derived from 10 dual-polarization SAR images with collocated wind directions from buoys, GPS dropsondes, scatterometer, radiometer, and Hurricane Research Division Real-time Hurricane Wind Analysis System (H*Wind) data. Statistical comparisons show that the wind direction bias and root-mean-square error are 3.22° and 21.53°, respectively. Subsequently, as a case study for Hurricane Maria, the retrieved wind directions, along with co- and cross-polarized GMFs are used to derive wind speeds. The retrieved wind speeds are validated with collocated Stepped-Frequency Microwave Radiometer (SFMR) measurements. The results show that the combination of co- and cross-polarized GMFs has capability of obtaining more reasonable hurricane wind speeds and directions than by only using co- or cross-pol GMF.