Measurement of surface currents using sequential synthetic aperture radar images of slick patterns near the edge of the Gulf Stream

Abstract

Two‐dimensional surface currents are estimated over an area of ∼100 km2 near the inshore edge of the Gulf Stream by correlating the surface slick patterns observed on two synthetic aperture radar (SAR) images collected about 20 min apart. The currents obtained from this analysis are found to agree well with shipboard acoustic Doppler current profiler (ADCP) measurements at 10 to 20‐m depths. The orientations of the long, linear slicks observed in this region differ from the mean current direction by about 16° but coincide with the direction of maximum radial deformation or strain, as calculated from the observed current field. The calculated current gradients indicate a mean surface convergence of about 2×10−5 s−1 and a cyclonic vorticity of about 1×10−4 s−1, values which fall within the range of previous estimates in the study area. These results suggest that slick patterns may be used to infer surface current magnitude and direction from a time sequence of SAR images but that care must be exercised in inferring current directions from the orientations of slick patterns within a single image.