Research For Motion Estimation Based On Multibeam Synthetic Aperture Sonar

As the continuous development of human society,the demand for marine resources is also growing. Synthetic aperture sonar is an efficient marine exploration tool that can provide strong technical support for the development of marine resources. When projecting the sonar returns onto the seafloor, ground range resolution deteriorates as range decreases. Any side-looking sonar will therefore have a gap around nadir, or at the very least, a sector with severely degraded performance. While the multibeam synthetic aperture sonar technology combines synthetic aperture sonar and multibeam bathymetric technology to achieve full coverage mapping area. It is no blind measurements with good development prospect.Due to the impact of the marine environment, multibeam synthetic aperture sonar carrier will deviate from the ideal trajectory, thus affecting the image quality, therefore the motion estimation and compensation techniques are effective means to improve the image quality of multibeam SAS. Imaging results are an important basis to test whether the motion estimation algorithm is effective or not, and the echo simulation algorithm is the basis of imaging studies.So the main contents of this paper contain three sections: echo simulation, imaging algorithm and motion estimation.The basic principle of multibeam SAS is studied from the SAS and multibeam bathymetric technology. Comparing the azimuth resolution of the real aperture with synthetic aperture sonar, discussing the selection of the pulse repetition frequency. The azimuth resolution of the multibeam bathymetric sonar changes with the mapping distance increases and the signal wave length, while the azimuth resolution of multibeam SAS is fixed, which only determined by the element aperture length. Finally, considering the velocity, hardware complexity and other factors,a multibeam SAS of multi-array structure is given.In echo data simulation, the error of the Hop-and-Stop and the displaced phase center is studied, the results show the error caused by the Hop-and-Stop can't be ignored, so we adopt the uniform motion models. In somatic target echo model, the point of the surface is used to calculate the echo delay and the four corners of the target is used to calculate the shadow area.Then the imaging algorithms of LFM signal and CW signals is studied. In azimuth synthesis algorithm, the paper adopt the most direct and the most accurate time-domain BP imaging algorithm to provide the support of the motion compensation. In order to solve the problem of the bathymetric resolution is limited by the beam number in the tradition multibeam SAS,a new multibeam SAS interferometric imaging algorithm is proposed.In the motion estimation of multibeam SAS section, firstly the paper analysis the impact of motion error for multibeam SAS image quality. The sonar platform has 6-DOF, Sway and Heave have great influence on the slant range of the target, the Roll impact on the beamforming across-track, the Yaw and the Pitch change the zone of sonar coverage. Then the Sway?Yaw and Roll were carried out estimation and compensation, the computer simulation results verify the effectiveness of the algorithm. Finally a new motion estimation algorithm of 6-DOF was proposed for the higher estimation accuracy, but it requires at least three non-collinear target in the imaging region.