基于多普勒频移的SAR海表流场反演

Estimation of Sea Surface Velocities from SAR Images Using the Doppler Shift

采用欧空局ENVISAT先进合成孔径雷达(Advanced Synthetic Aperture Radar,ASAR)宽幅模式(Wide Swath Mode,WSM)数据,基于多普勒频移理论模型去除地球和卫星相对运动产生的频移,并用C波段经验模型CDOP(C Band Doppler Frequency)和双尺度辐合散射模型分别去除海面风场和布拉格散射的影响,从而实现高分辨率海表流场的反演,并将反演结果与AVISO(Archiving,Validation and Interpretation of Satellite Oceanographic Data)高度计流场和GLD(Global Drifting Buoy)漂流浮标流场进行精度验证。分别选取有陆地覆盖的厄加勒斯海域和无陆地覆盖的台湾东北部黑潮流域进行反演研究。研究结果表明:厄加勒斯海表流速范围约-1.8～1.8 m/s,流向与AVISO流场较为一致;在黑潮流域,反演的ASAR流场能够明显地揭示黑潮的路径和流向,且与AVISO流场匹配较好。综合反演结果表明ASAR流场与AVISO流场的均方根误差为0.17 m/s,与漂流浮标GLD流场的均方根误差为0.11 m/s。可见此流场反演方法切实可行,同时适用于近岸和开阔海域,且反演精度较高。

The sea surface velocities field plays an important role in seawater exchange and substance transportation.In this paper,the Wide Swath Mode(WSM)data derived from the ENVISAT Advanced Synthetic Aperture Radar(ASAR)are used to retrieve the high-resolution sea surface velocities field.based on the theoretical model of SAR Doppler shift,the errors caused by the relative motion between Earth and satellite are removed.Then we use the C Band Doppler Frequency Model(CDOP)and the Bragg scattering model to remove the errors caused by the sea surface wind and Bragg scattering,respectively.The data used to verify the accuracy of the retrieval results are AVISO(Archiving Validation and Interpretation of Satellite Oceanographic)velocities and the GLD(Global Drifting Buoy)velocities.Our method is applied both in the coastal area with land cover(Agulhas)and the open sea(Kuroshio)without any land.Results show that in Agulhas,the velocity ranges from-1.8 m/s to 1.8 m/s,and their directions agree very well.In the Kuroshio,the ASAR current can clearly reveal the flow path and direction of the Kuroshio,and it matches well with the AVISO current.The comprehensive results shows,the Root Mean Square Error(RMSE)of ASAR and AVISO is 0.17 m/s,and the RMSE of ASAR and GLD is 0.11 m/s.This implies that the methods used here not only simplified the processes but also has high accuracy to retrieve sea surface velocities both in the coastal area and in the open sea.