Joint Motion Error Estimation Algorithm for Multibeam Synthetic Aperture Sonar

Multibeam echo sounder (MBES) and synthetic aperture sonar (SAS) are effective image sonar systems used as the major underwater observation instruments. The MBES system can get the full-scan detection without gaps, while the resolution on the along-track is limited by the beam width and the range. The SAS system can provide the high resolution independent of signal frequency and range, while the accurate height information cannot be obtained directly and the gaps always exist. Multibeam SAS (MBSAS) is a new type of imaging sonar that combines the advantages of MBES and SAS. Through the MBSAS imaging algorithm, the full-scan 3-D detection without gaps can be obtained with high resolution. In a single synthetic period, the carrier should move linearly as an ideal track to guarantee the validity of the synthesis algorithm. However, the carrier’s motion error always exists in the actual situation. Thus, the carrier’s motion error should be estimated and compensated effectively to avoid the sonar image being defocused. In this paper, an echo model of MBSAS is proposed and an imaging algorithm is deduced to analyze the error of the imaging algorithm, which is caused by the motion error. The motion error is divided into six dimensions and separated into two types as the position error and the motion attitude error. The defocusing problem is caused by the joint motion error influences rather than the single dimension. A kind of joint motion error estimation algorithm is also proposed to estimate the motion error of the carrier. Through the simulation study, the feasibility and the performance of the algorithm are demonstrated. Simulation results indicate that the motion error can be estimated and the image defocusing problem can be handled effectively.