Ocean surface current in tropical cyclones extracted from RADARSAT-1 ScanSAR raw data

Space-borne SAR (Synthetic Aperture Radar) has been one of the most effective tools for physical oceanographic and air-sea interface research. We applied the effect of Doppler shift observed in the raw SAR data to estimate ocean surface velocity. Relative motion between sensor and Earth´s target causes Doppler shift of radar signal which can be recorded in SAR signal data. The relative motion can be derived by comparing the difference between target Doppler centroid and reference Doppler centroid. The reference Doppler centroid is a Doppler centroid that corresponds to the stationary area or a fixed target. The reference Doppler centroid can be calculated with the geometry model on the rotating Earth. On the other hand, the target Doppler centroid was estimated by applying the correlation Doppler estimator to the RADARSAT-1 ScanSAR raw data (also known as the Average Cross Correlation Coefficient; ACCC). Target Doppler centroid is caused by the movement of upper ocean waterbody. By comparing of these two Doppler centroids, line-of-sight velocities of ocean surface can be retrieved. Until recently, studies to characterize and quantify oceanic response to tropical cyclones such as typhoon and hurricane have rarely reported because of its difficulty of observation under these extreme conditions. The object of this study is to extract more accurate ocean surface velocity response to tropical cyclones from RADARSAT-1 ScanSAR raw data. In the future, we will be able to investigate oceanic response to tropical cyclones from the estimated ocean surface velocities.