A comparison of interferometric radar surface velocity measurements to subsurface current structure

Remote sensing of the ocean surface using interferometric SAR (INSAR) is of significant interest due to it's potential for surface current measurements over large areas. INSARs use the phase difference between colocated SAR images separated by a small time lag to infer surface Doppler velocities, and hence wave orbital velocities and currents. It is not clear, however, how representative INSAR measurements may be of actual currents in the water column. This paper presents comparisons between surface Doppler velocity measurements and subsurface water currents. Imagery from an X-band, focused phased-array radar is analyzed to yield both ''interferometric'' surface velocities and subsurface current estimates derived from dispersion characteristics of the imagery. The radar-derived velocities, combined with coincident Acoustic Doppler Current Profiler (ADCP) measurements are used to generate a vertical profile of current in the water column. Case studies are presented under varying environmental conditions for which the vertical structure alters considerably. The sensitivity of X-band interferometric measurements to wind-drift and the near-surface current structure is revealed.