Velocity-ISAR: On the application of ISAR techniques to multichannel SAR imaging

The U.S. Naval Research Laboratory (NRL) Multichannel Synthetic Aperture Radar (MSAR) consists of multiple receive channels arranged along the flight direction and is unique in its ability to measure and correct for radial motion at each pixel in the scene. A well-known algorithm for performing MSAR imaging, and which have we applied for the first time to data captured by an airborne system, is the Velocity Synthetic Aperture Radar (VSAR) algorithm. VSAR calculates the distribution of Doppler radial velocities associated with each pixel and subsequently compensates for the velocities in order to combat motion blur. However, as we demonstrate in this paper, the VSAR algorithm does not fully exploit the special structure associated with the motion dynamics of rigid bodies (including translational and roll-pitch-yaw motions) in maritime conditions. To this end we propose the use of Inverse Synthetic Aperture Radar (ISAR) based motion compensation techniques-in conjunction with velocity filtering-as a means of accomplishing this objective for MSAR imaging. After describing the rudiments of the NRL MSAR system and the basics of ISAR processing, we subsequently proceed to describe our proposed Velocity-ISAR (VISAR) imaging algorithm. We demonstrate the performance of our VISAR algorithm by imaging boats captured by our airborne NRL MSAR system; and highlight its relative advantages over VSAR in imaging maritime targets.