A Systematic Comparison of the Effect of Polarization Ratio Models on Sea Surface Wind Retrieval From C-Band Synthetic Aperture Radar

Geophysical model functions (GMFs) for deriving sea surface wind from C-band synthetic aperture radar (SAR) are usually developed and well validated for VV-polarized data, e.g., CMOD5. For wind retrievals from HH-polarization data acquired by some SAR satellites, e.g., RADARSAT-1, part of RADARSAT-2 and ENVISAT ASAR, various Polarization Ratio (PR) models are used to convert normalized radar cross sections (NRCS) from HH to VV polarizations before a GMF is applied. In this study, 116 dual-polarization (VV and HH) C-band ENVISAT Advanced SAR (ASAR) Alternating Polarization (AP) mode images are collected to analyze the behavior of different empirical and theoretical PR models in SAR HH wind retrieval. A new PR model is also developed by analyzing ENVISAT ASAR AP data. SAR HH winds from CMOD5+PR models are validated against SAR VV winds from CMOD5 only. Results show that the proposed new PR model in conjunction with the CMOD5 GMF can constitute promising hybrid GMFs for wind speed retrievals with HH-polarized ENVISAT ASAR images.