Research On The Key Technology Of Bathymetric Sidescan Sonar

With the development and use of ocean resources, underwater acoustic detection hasbecome a very hot topic, and undersea topography detection is the first step in the developmentof the ocean and its importance is self-evident. Currently seafloor topography detection is mainlydepended on two important instruments: sidescan sonar and multi-beam bathymetric sonar (thesynthetic aperture sonar is based on sidescan sonar, which could be regarded as a kind ofsidescan sonar in general), which have their own advantages. Sidescan sonar has high lateralresolution, which is mainly used to detect seafloor topography; multi-beam sonar can accuratelymeasure the depth of the seabed and form intuitive three-dimensional topographic maps, whichis mainly used to detect undersea terrain. In order to combine the advantages of these two sonartechnologies to form a kind of sonar, which not only has side scan function, but also hasbathymetric function, Denbigh proposed the principles and structure of the bathymetric sidescansonar system formally in1977for the first time. It develops from the side-scan sonar, and thushas all the advantages of side-scan sonar; As for the structure, it increases the number of arrayelements parallel with the transmitter array to receive the echo signal, and then uses the phaseinformation between different receiving array elements to estimate the bottom of instantaneousecho’s direction, so that we can calculate the depth of the seabed, which can be same as themulti-beam sonar with the depth measuring function with tape. Compared with multi-beambathymetric sonar, bathymetric sidescan sonar has more bathymetric probe points and they canremain the same position with side-scan probe points, which makes the data integration betweenthe bathymetric probe points and the side-scan probe points easier. It should be noted thatbathymetric sidescan sonar also has its disadvantages: sounding accuracy is limited by thestructure itself, so it is very difficult to achieve high sounding accuracy.In this paper, the author has done a series of studies about some key technologies ofbathymetric sidescan sonar, which are also the main content of this article:Firstly, the author studies the seabed backscatter theory, and sums up the general rules of theseabed backscatter. And then the Jackson scattering model is introduced and used to calculate theseabed backscatter strength. And the author combines it with the sea trial test data to verify thecorrectness of the Jackson scattering model.Secondly, the side-scan imaging principle and bathymetric imaging principle are detailedintroduced. According to the two features of bathymetric sidescan sonar-a small number ofreceiving array elements and few snapshots to estimate azimuth, the author focuses on the threepossible bathymetric algorithms: differential phase algorithm, sub-array space fitting algorithm and algorithm based on Prony principle and discusses the performance and applicability of thesealgorithms.Concerning the feasibility of bathymetric sidescan sonar, detailed analysis of someperformance parameters of bathymetric sidescan sonar are made. And bathymetric errors andsounding accuracy assessments are theoretically analyzed and studied. Especially the soundingerror correction has a very important significance in the actual bathymetric process.The simulation is an important tool for applying the theory to the practical engineering, andthis paper has made a lot of simulation work about bathymetric sidescan sonar signal processing,that is, from receiving submarine echo signal simulation to the side-scan sound map simulation,and then the author uses the three sounding algorithms to estimate coherent signal DOAsimulation and uses sounding algorithm to estimate the depth of three different two-dimensionalseafloor topography simulation and finally estimates the depth of three-dimensional seafloortopography simulation. Through these simulation studies the correctness of bathymetric andside-scan principles are demonstrated and they indicate the direction for the signal processing ofthe actual data.Finally, the actual experimental data are detailed analyzed and processed. On the aspect ofside-scan sound map, the author puts forward the fusion of a weighted multi-array elementsidescan sound map and a single array element sidescan sound map, which eliminates some ofthe secondary reflection ghosting and improves the quality of sidescan sound map. And then theeffects of sound speed profile before and after sounding correction are analyzed and the fact isindicated that sound speed profile is an important factor of affecting the sounding errors.Through the algorithm based on Prony principle the actual data are processed, and the authorobtains the bathymetric sound map corresponding to the side-scan sound map, and analyzes thetopography features that the two sound maps reflect are coincide and complement each other.Finally, in order to obtain more intuitive and precise side-scan sound map and bathymetric soundmap, the author uses the Caris software to process the actual data and form mosaic sound mapand correct the geographic coordinate position on the sound map.