An investigation of inversion method to measure the radial velocity of Kuroshio from Sentinel-1 SAR data

Abstract

ABSTRACT Studies on the retrieval of ocean surface current by Synthetic Aperture Radar (SAR) mainly concentrate on coastal regions with land coverage, allowing for continuous land to estimate non-geophysical Doppler shifts. As a strong western boundary in the Western Pacific, the Kuroshio flows through mostly islands or open sea, and lacks land coverage for range bias correction. We propose a non-geophysical Doppler shift correction algorithm suitable for Kuroshio observation. Three solutions matching different land coverage were adopted in the range direction, and the scalloping was removed by using average filtering in the azimuth direction. Comparison between SAR radial velocity and Global Surface Lagrangian Drifter (GLD) reveals that the correlation coefficient (R 2) increase to 0.686, and root mean square error (RMSE) of 0.215 m/s after non-geophysical corrections, while the wind-wave bias corrections make R 2 increase to 0.806 and RMSE decrease to 0.13 m/s. There is also a good consistency between SAR inversion and Regional Ocean Circulation Model (ROMS). Sensitivity analysis illustrates that ascending pass is more suitable for monitoring Kuroshio, and high incidence angles are less affected by ocean conditions and non-geophysical factors. The algorithm can be used in regions with discontinuous or absent land.