Estimation of ocean surface velocity in tropical cyclones using RADARSAT-1 ScanSAR raw data

Space-borne Synthetic Aperture Radar (SAR) has been one of the most effective tools for physical oceanographic and air-sea interface research because the direct observation of ocean surface currents response to tropical cyclones such as typhoon and hurricane is limited under various extreme conditions. Relative motions between a sensor and Earth´s target causes Doppler shift of radar signal which can be recorded in SAR signal data, and we employ the effect of Doppler shift observed in the raw SAR data to estimate ocean surface velocity. The ocean surface velocity in the Line-of-Sight (LOS) direction can be derived by comparing the anomaly between the prediction of the Doppler centroid using geometry model and the estimation of the Doppler centroid using the Correlation Doppler Estimator (CDE). Moreover, the net Bragg-wave phase velocity, a component of the surface currents, is subtracted from the ocean surface velocity in order to derive the actual ocean surface current velocity. Until recently, studies to characterize and quantify oceanic response to tropical cyclones have been rarely reported because of its difficulty of observation under these extreme conditions. The object of this study is to extract more accurate ocean surface current velocity response to tropical cyclones using RADARSAT-1 ScanSAR raw data.