An interferometric approach to ocean surface velocity imaging using multi-channel SAR

This paper presents a new interferometric approach to forming ocean surface velocity images using a multi-channel synthetic aperture radar (SAR) with M equally-spaced phase centers arranged in an along-track configuration. The technique coherently combines the M-1 shortest-baseline interferograms to produce motion estimates with superior velocity resolution, as compared to those produced by both the Velocity SAR technique as well as by an alternative interferometric method that analyzes the phase progression across a sequence of M-1 interferograms with progressively longer baselines. The new single-baseline approach also provides the widest possible unambiguous Doppler range, owing to the use of the shortest available baseline. The technique is analyzed theoretically and illustrated experimentally using ocean imagery collected with a multi-channel SAR system that supports 16 along-track phase centers.

I. Introduction

Multi-channel synthetic aperture radar (MSAR) has numerous applications in dynamic maritime environments, including target detection and identification, surface current mapping, and wave monitoring [1]–[6]. Key to these applications is MSAR's ability to measure scene motion through the use of multiple along-track phase centers. If two phase centers are available, the motion information can be extracted from the MSAR data using along-track interferometric SAR (ATI-SAR) techniques [7] [8]. If many phase centers are available, the Velocity SAR (VSAR) algorithm can be applied to measure the full spectrum of motion at each and every pixel in the image and to correct the image distortions that the scene motion induces [4]–[6]. However, VSAR's velocity resolution is limited by the length of the phase center array, and it can be impractical to implement a system with precision fine enough to measure ocean currents and wave velocities.