A Novel Motion Compensation Scheme for 2-D Multichannel SAR Systems With Quaternion Posture Calculation

The displaced phase center antennas in azimuth and digital beamforming (DBF) in elevation are two state-of-the-art techniques for achieving high-resolution wide swath (HRWS) imaging in the multichannel synthetic aperture radar (SAR) systems. However, due to the atmospheric turbulence, airborne HRWS-SARs inevitably suffer trajectory disturbances, which will consequently defocus the SAR image. Although various motion compensation (MoCo) methods have been proposed, they are mostly designed for the traditional single-channel SAR and, therefore, ignore the channel-dependent posture error. The posture motion error will introduce residual motion and time-variant channel errors, which not only defocuses the image but also causes azimuth ambiguity and degrades the SNR improvement of the final images of the azimuth multichannel and DBF-SAR, respectively. To solve these problems, a novel MoCo scheme for 2-D multichannel SAR systems is proposed. The posture error is described and calculated in matrix form through the use of quaternions. Then, the posture error is transformed into the translational motion error for each receiving channel and is subsequently compensated precisely. To address the residual aperture-variant motion error, a modified aperture-dependent MoCo is integrated into the proposed scheme. Simulations and airborne experiments, including processing the data of a C-band SAR system with four azimuth channels and an X-band DBF-SAR system with 16 elevation channels, have been implemented to validate the effectiveness of the proposed MoCo scheme.

I. Introduction

In order to achieve high-resolution wide swath (HRWS) imaging and realize diversified applications, 2-D multichannel synthetic aperture radar (SAR) system designs, i.e., azimuth multichannel combined with digital beamforming (DBF) for elevation, are considered to be the state-of-the-art techniques [1]–[3]. The azimuth multichannel SARs utilize the displaced phase center antenna technique to reduce the high requirement of pulse repeat frequency (PRF) [4], [5]. Besides, azimuth multichannel SAR is widely used in ground moving target indication [6]–[8]. Furthermore, to enhance the SNR of SAR images in a wide swath, DBF on reception [9]–[11] is a promising technique for spaceborne SARs [12]. Since 2-D multichannel is the current trend of HRWS SAR system design [13], airborne azimuth multichannel SAR and DBF-SAR systems have gradually been developed for experimental verification and applications [14], [15].