Ocean Surface Current Measurement with an Interferometric UHF SAR

In this paper, we report initial results of an experimental investigation into measurement of ocean surface currents with an ultra high frequency synthetic aperture radar (UHF SAR) that supports an along-track interferometric (ATI) mode. We first describe the unique system, the NRL Multiband SAR, used to collect the data. We then present initial results related to two different approaches to current measurement. In the first approach, the surface current is estimated using standard ATI-SAR processing. We show progress in the implementation of this method with an interferometric phase cut across the north wall of the Gulf Stream. In the second, a time-sequence of images of propagating wave-like patterns is first generated using sub-aperture processing of the wide-beam, strip-map data, and this sequence is then transformed into wavenumber-frequency space through a 3D FFT. The surface current is then estimated from the displacement of the wave energy relative to the theoretical surface wave dispersion relation in the absence of any underlying current. We illustrate our progress in this approach with a wavenumber-frequency analysis of a 41-second sub-aperture image sequence of propagating waves.