Estimating ocean surface velocity and coherence time using multichannel ATI-SAR systems

Conventional along-track interferometric synthetic aperture radars (ATI-SARs) derive the ocean surface velocity from an estimate of the phase difference between the SAR echoes received from two displaced phase centres with a single time-lag. The authors propose an efficient asymptotic maximum likelihood (ML) algorithm for jointly estimating the ocean surface velocity and ocean coherence time by using multichannel SAR data collected from an array of phase centres with multiple time-lags. The method combines a covariance matching algorithm with the use of the extended invariance principle (EXIP). Simulated results show that the proposed technique provides better estimation accuracy than the conventional two-channel system. Moreover, it provides unambiguous velocity retrieval and flexibility to varying ocean coherence time