SAS In RD Algorithm And Improved Imaging Based Motion Compensation

Synthetic aperture sonar (SAS) originated in synthetic aperture radar field which is applied to the sonar field in the1960s. SAS is a new kind of high resolution imaging sonar whose basic principle is that the platform moves along the azimuth to synthesize a virtual large aperture instead of a small aperture, in order to obtain high azimuth resolution. High range resolution depends on the technology pulse compression. Synthetic aperture sonar plays an important role in the field of the development of marine resources, the protection of cultural relics, topographic surveying and mapping, underwater rescue and so on. Actually, people increasingly pay much attention to synthetic aperture sonar.Researchers attached importance to the research on synthetic aperture sonar imaging algorithm, so this paper mainly studies the range Doppler (RD) algorithm which is classic and used nowadays. The algorithm mainly includes three processing modules:range compression, range cell migration correction that is the core of the algorithm and azimuth compression. Generally speaking, RD is applied to SAS in the case of ideal trajectory. However, the sonar carrier is influenced by the factors such as ship joystick and waves and so on in the practical application. Therefore, SAS deviates from the ideal track and causes motion error which affects the quality of SAS imaging. So we systematically studied the motion error and compensation methods, and proposed an improved algorithm of RD in the fourth chapter. Finally, the improved algorithm of RD is used to carry out simulation experiments, the quality of imaging is good. Therefore, results verify the effectiveness and feasibility of the improved algorithm. The detailed contents are as:1. This paper discusses a kind of classical imaging algorithms-range Doppler algorithm. Based on the basic knowledge mentioned in the second chapter, We analyses implementation steps and formula derivation of RD.As we all know, RD includes three processing modules which are range compression, range cell migration correction and azimuth compression.Actually, different methods for range cell migration correction produce different imaging algorithms. Simulation experiments for five point targets, a planar target and a three-dimensional target are carried out, the quality of the imaging is good. However, RD doesn’t take motion error into consideration.2. This paper studies the motion error and motion compensation. In practical applications, SAS which is influenced by the marine environment often deviates from the ideal track and causes motion error. The motion error is mainly translational motion error which will change the Doppler centroid and the phase information of the echo signal. After processing the echo signal through matching filters and range cell migration correction, the SAS image will appear defocusing, eventually leading to the decline in the quality of imaging. The translational motion error can be decomposed into the line of sight error and velocity error which all affect the imaging quality. Therefore, this paper mainly analyzes the two kinds of motion error and the compensation methods.3. This paper puts forward an improved algorithm of RD which is based on motion compensation. Motion error results in the change of the phase of the echo signal, so the improved algorithm of RD needs to compensate the phase error of the echo signal. That is to say that that mentioned processing is to filter for the echo signal. Envelope correction and follow-up interpolation is needed after the Fast Fourier Transform for the range. Finally, the improved algorithm of RD is used to carry out simulation experiments for five point targets, a planar target and a three-dimensional target, results verify the effectiveness and feasibility of the improved algorithm.