Research On Synthetic Aperture Sonar Imaging Technology Based On Bistatic Model

Synthetic aperture sonar(SAS)originated in the field of synthetic aperture radar,is a new type of high-resolution underwater detection equipment.The basic principle of SAS is that a physical small array moves along the azimuth direction to synthesize a virtual large aperture and thus obtain high azimuth resolution.Moreover,with rich information,strong anti-interference and high concealment,bistatic synthetic aperture sonar(BISAS)has wide development prospects both in military and civil activities.As sonar and radar have a lot of similarities,SAS can adopt some technological achievements of SAR.However,under the influence of complex underwater envi-ronment,SAS has greater challenges than SAR.First,the multipath effect in under-water acoustic channel is more severe than in the air,leading to ghost targets in SAS images.Second,sonar is difficult to maintain stable movement under the influence of waves and currents.Last,low velocity of sound in water makes sonar move slowly to ensure adequate samples.In addition,high-resolution imaging requires large amounts of data,which creates much pressure on SAS system.Based on the above problems,BISAS is taken as a case study in this paper.And the main contents can be summa-rized as follows:(1)To solve the degradation of BISAS image quality caused by multipath effect,a method of combining virtual time reversal mirror and synthetic aperture imaging al-gorithm is proposed in this paper.The channel estimation is carried out by matching correlation method,and the principle of time reversal is used to suppress the multipath interference in the echo signal.Finally,BISAS imaging processing is performed.Simulation results show the validity and the anti-multipath performance of the pro-posed algorithm.(2)The motion error model in BISAS and its impact on the imaging are studied,and then the error components in the echo data are extracted and compensated.The residual error after motion compensation is processed by strip-map phase gradient autofocus algorithm(PGA),and an adaptive window-width estimation method is proposed to improve the windowing strategy.Simulation results verify the validity of the motion compensation and autofocus algorithm.(3)To reduce the amount of data in BIS AS system,BIS AS imaging algorithm based on two-dimensional compressed sensing is proposed in this paper.By analyzing the characteristics of the echo signal,sparse representation models are successively constructed in the range and azimuth direction.Finally,the imaging results can be ob-tained by sparsity adaptive matching pursuit(SAMP)algorithm.Compared with the bistatic R-D algorithm,two-dimensional compressed sensing imaging algorithm needs less sampling for imaging,and effectively suppress the sidelobes.The proposed algorithm can get high-quality images.