ROUTINE HIGH RESOLUTION OBSERVATION OF SELECTED MAJOR SURFACE CURRENTS FROM SPACE

摘要

Over the ocean a radial velocity can be derived from thernDoppler frequency shift measured in SAR scenes as thernobserved Doppler centroid frequency is subtracted fromrnpredicted. This radial (range direction) velocity can inrnturn be related to geophysical quantities such as the nearrnsurface wind and surface current. As alreadyrndemonstrated by Chapron et al. [1] the Doppler shift isrnat first order highly correlated with the radial windrnspeed. Using comparisons with ECMWF wind fields, arnneural network is used to reproduce the dependency ofrnthe Doppler shifts (or anomalies with the vector windrnfield and incidence angle. Using this empirical model,rnthe wind impact on the Doppler anomaly can bernsystematically removed to exhibit more clearly the searnsurface current signatures. This methodology is appliedrnto the equatorial and counter-equatorial currents in thernPacific using ASAR wave mode (WM) imagetternproducts as well as to the greater Agulhas currentrnregime off South Africa using ASAR wide swath modern(WSM) products.