Conventional along-track interferometric synthetic aperture radars (ATI-SAR
s) derive the ocean surface velocity from an estimate of the phase differen
ce between the SAR echoes received from two displaced phase centres with a
single time-lag. The authors propose an efficient asymptotic maximum likeli
hood (ML) algorithm for jointly estimating the ocean surface velocity and o
cean coherence time by using multichannel SAR data collected front an array
of phase centres with multiple rime-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 estim
ation accuracy than the conventional two-channel system. Moreover, it provi
des unambiguous velocity retrieval and flexibility to varying ocean coheren
ce time.