Trajectory Deviations in Narrowbeam SAS: Analysis and Compensation

Abstract

The effect that motion errors have on synthetic aperture sonar (SAS) imagery can be severe, and motion compensation (MOCO) is one of the difficult problems in SAS imaging. This paper studies the compensation of trajectory deviations and imaging algorithms in SAS. The range history model and motion error expression of multiple-receiver SAS deviating from the nominal trajectory are derived in the nonstop-and-hop mode and the condition of neglecting the aperture dependence of motion errors is given. With the analysis of the range space variance of motion errors, it is found that motion errors, under the condition of typical SAS parameters, are far greater than one range resolution cell because of the wide relative swath, and the range space variance of range position errors cannot be neglected. Most of the existing MOCO methods that account for known deviations of the platform trajectory in SAS are combined with the time-domain beamforming algorithm, which is computationally expensive. And a few are combined with block reconstruction algorithms, but draw on the two-step MOCO in SAR and are not suitable for SAS. This paper proposes a MOCO method that the range position errors are compensated by interpolation after range compression and the corresponding phase errors are compensated by phase multiplication. Then the wide-swath MOCO and imaging are realized by combining the proposed MOCO method with CZT algorithm. Simulated data sets validate the effectiveness of the proposal.