Research On The Key Technology Based On Multi-Beam Synthetic Aperture Sonar

In recent decades,imaging sonar has been widely researched and developed as different technology branches,including the side scan sonar(SSS),synthetic aperture sonar(SAS)and multibeam echo sounder(MBES).MBES can achieve 3D full-scan acoustical detection,while the resolution on the along-track decreases seriously with the detecting distance,limited by the beam footprint.SSS can achieve a narrow beam width to manage the footprint,the resolution on the along-track also decreases inevitably.SAS obtains a constant resolution on the along-track owing to the synthetic processing,but the problem of gaps always exists that needs an additional filler.What's more,the depth accuracy of SSS and SAS may be limited,which is obtained by the dual elements coherent detection or the shadows inversion.In this paper,the advantages of different imaging technologies are combined to overcome the shortcomings that the multibeam synthetic aperture sonar(MBSAS)is studied.The echo model of MBSAS is proposed based on the 2D transducer array that the feasibility of the technology is verified through the theoretical analysis and tank experiment.The researches focus on the detecting theory and array design,target model and echo simulation,imaging algorithm,motion error estimation and compensation,and the tank experiment analysis.1.A novel detection theory of MBSAS is proposed based on the 2D transducer array after the analysis of the MBES and SAS detecting system.The processing scheme of MBSAS is built and the grating lobe problem of MBSAS is analyzed through the theory and the simulation.The methods to manage the lobe problem can be described as two steps:transducer array design and the signal processing theme,including the multi receiving array on the along-track,large element spacing array,wide bandwidth signal detection and so on.Working parameters of the transducer array have been designed and the array is processed.The performance of the transducer array has also been verified through the tank experiment.2.A kind of 3D target echo simulation method is proposed based on the highlights model.The complex target echo model is divided into the superposition of many sub highlights echoes.Analytical solution of the positions of the elements at a different time is derived under the cartesian coordinate system based on the 2D transducer array.The echo time delay is also derived based on the 2D echo model under the coordinate system of y-r-?.Data simulation is taken when the carrier locates at different positions,including the seabed,3D target,and the shadows area.Moreover,a fast simulation method based on the SFS model is proposed,which does not need the analytical derivation of the complex target.3.3D point by point imaging algorithm is proposed to increase the fineness of sonar images.The analytical solution of the imaging is based on the MBSAS theory and model.The signle highlight,adjacent cube target,shadows area and the complex target has been simulated base on the researches above to verify the performance of the MBSAS imaging algorithm.A kind of target echo detection method based on the inner beam fitting is proposed to sparse the 3D sonar image.What's more,a transducer array calibration method is proposed to overcome the machining error based on the minimum residual criterion.The accuracy of the method is compared with the cramer-rao bound and the filed data processing.4.To manage the defocusing problem owing to the carrier's moving error,a kind of motion estimation method based on the nonlinear overdetermined equations is proposed.The carrier's moving error is divided into position error and attitude error that 6D motion error's influence on the imaging has been analyzed.A joint motion error estimation method is proposed which considers the motion as a whole factor to manage the defocusing problem.The gradient method is employed to solve the nonlinear overdetermined equations that the6 D motion can be obtained at the same time.The performance and the feasibility of the method have been verified through the theory analysis and the data simulation.5.The feasibility and performance of the MBSAS theory are verified through the tank experiment with different preset targets.The first experiment is carried based on the dual ball targets that the imaging processing is taken by the algorithms such as SSS,SAS,MBES,and MBSAS of 2D or 3D space.The imaging results are sliced compared that the conclusion comes as the MBSAS theory can detect the small targets detailly with a better energy focusing ability.Secondly,the methods to manage the grating lobe problem discussed above have also been verified through the experiment including the multi receiving array on the along-track,large element spacing array,wide bandwidth signal detection.The synthetic aperture's influence on the imaging has also been discussed through the tank experiment data processing.Finally,a cube target detection experiment has been taken to show the advantages of MBSAS to indicate the target's number,location,size,and shape with a better energy focusing ability than MBES.