Retrieval of Significant Wave Height under Typhoon Conditions from Gaofen-3 SAR Imagery

The objective of this paper is to propose an empirical method to inverse significant wave height (SWH) under typhoon conditions from collected dual-polarization Gaofen (GF)-3 synthetic aperture radar (SAR) imagery. The typhoon scenes were captured from narrow scan (NSC) and wide scan (WSC) images, and collocated with European Center for Medium-Range Weather Forecasts reanalysis data of (ECMWF). To improve the quality of GF-3 SAR images, the recalibration over rainforest and de-scalloping were carried out. To establish the empirical relationship between SAR-derived parameters and collocated SWH, the sensitivity analysis of typical parameters about the normalized radar cross section (Nrcs) and imagery variance (Cvar) were performed to both VV and VH polarized images. Four scenes from GF-3 SAR imagery under typhoon conditions were used for training the model by the multivariate least square regression, and one scene was used for preliminary validation. It was found that the joint retrieval model based on VV and VH polarized SAR imagery performed better than any single polarized model. These results, verified by using ECMWF data, revealed the soundness of this approach, with a correlation of 0.95, bias of 0 m, RMSE of 0.44 and SI of 0.01 when VV polarization and VH polarization data were both used.