SAS Shek Side CS Imaging Algorithm And Improvement Oblique Perspective

Synthetic Aperture Sonar (SAS) is new high-resolution underwater imaging sonar. By using a virtual aperture instead of the real aperture, not only the problem of aperture size, but also the problem of azimuth resolution is solved. Unlike ordinary sonar, the main advantage of SAS is that it can get high azimuth resolution and it has broad application prospects.The research on high-resolution SAS imaging algorithm has been always one of the hot technologies in the field of SAS. Although the most classic image processing algorithm is RD algorithm, the main drawback of the RD algorithm is that the interpolation processing causes a rapid increase in the amount of computation, and reduces the imaging precision. Range migration correction (RMC) and secondary range compression (SRC) is achieved precisely in the CS algorithm, also the interpolation is avoided. Nonlinear CS algorithm is an improved algorithm of original CS algorithm and compared with CS algorithm, it can achieve better results in the imaging processing of squint mode SAS.Considering the above problems, in this thesis, the specific contributions are introduced as follows:(1) The basic theory of imaging in SAR is studied. More precisely, the characteristics of the time-domain waveform and the amplitude-frequency of LFM signals are analyzed. Moreover, pulse compression technology is analyzed, which is the basic of the imaging processing.(2) The point target model of SAR is given. Based on the classical broad side SAS mode imaging system, the SAS point target imaging geometry model is given and the expression of the target returns is derived, and some simulation results are given.(3) The characteristics of squint mode SAS system and the broad side SAS mode system are compared and analyzed, and this thesis mainly focuses on the problem of range migration correction. Doppler frequency characteristic, azimuth resolution, two-dimensional coupling phenomena and the direction spectrum is fully studied.(4) This thesis uses the linear CS imaging algorithm in the point target imaging to solve the problem of RD algorithm countered in the high-resolution imaging of SAS. The every step of linear CS imaging algorithm is derived and analyzed. Simulation results of point target imaging in the side S AR are given. Simulation results show that, compared with RD algorithm, CS algorithm improves the computational efficiency and phase accuracy. However, the CS algorithm is not satisfied the need in the squint mode SAS system.(5) An improved CS algorithm, i.e. nonlinear CS algorithm, based on the squint mode SAS is proposed in this thesis. The algorithm is derived in details and also gives the simulation results on point target. Moreover, simulation results of the two imaging algorithm in different oblique side are given and analyzed. Nonlinear CS algorithm can satisfy the high-resolution imaging SAS in certain oblique angle, and it is of significant meanings in the practical applications.