Impact of Polarization Basis on Wind and Wave Parameters Estimation Using the Azimuth Cutoff From GF-3 SAR Imagery

The azimuth cutoff wavelength of synthetic aperture radar (SAR) is an important parameter for retrieval of sea surface wind and wave. Earlier studies have fully demonstrated the substantial dependence of azimuth cutoff wavelength on polarization, but the present studies only focus on horizontal and vertical (H-V) linear polarization bases [horizontal-horizontal (HH), horizontal-vertical (HV)/vertical-horizontal (VH), and vertical-vertical (VV)] without considering the effects of other polarization bases (e.g., linear rotated, circular, and elliptical polarization). Benefiting from the quad-polarization advantage of GaoFen-3 SAR wave mode data and the support of polarization basis transformation theory, this study used 4648 SAR data to study the correlation between cutoff wavelength and wind and wave parameters (e.g., significant wave height and wind speed) under different polarization bases and analyzed the variation of correlation coefficient caused by polarization basis change. Finally, the results were applied to evaluate the performance of wind and wave parameters retrieval. The results of the study show that the azimuth cutoff is strongly dependent on the polarization state of the electromagnetic wave. The azimuth cutoff wavelength under the elliptical polarization bases has a higher correlation with wind and wave than that under H-V linear, circular, and linear rotated polarization bases. Using the azimuth cutoff wavelength of the elliptical polarization bases can significantly improve the retrieval accuracy of wind and wave parameters. This study shall enhance the capabilities of polarized SAR systems to precisely derive more ocean surface properties. The result implies that polarization basis is an important factor that must be considered in future ocean SAR studies.