The Application Of Multibeam Sonar Water Column Image In Middle And Bottom Water Target Detection

Multibeam echo sounder(MBES)system,as the current mainstream equipment for marine surveying and mapping,has the advantages of wide measurement range,fast speed and high accuracy.Large-area bathymetry and seabed backscatter intensity data can be obtained efficiently by MBES.In addition to recording the bathymetry and intensity information,the new generation multi-beam system can also detect the acoustic scattering of objects in the water column and record it as water column data(WCD).The processing,identification and application of WCD is one of the hot spots of multi-beam application research.Focusing on the detection and application of targets in the mid-bottom waters,this article analyzes the multi-beam sonar water column image(WCI).Taking two typical targets,i.e.the submarine sunken ship and the ocean internal waves,as the research objects,the detection,recognition and application of WCI are studied to expand the application field of MBES,and improve the accuracy of seabed topographic measurement in complex environment.The main work is as follows:1.The imaging mechanism,influencing factors and mapping method of MBES water column are systematically described.Through detailed analysis of the characteristics,advantages and disadvantages of the multi-perspective images generated by the water column data,the influencing factors of the multi-beam water column imaging are summarized and interpolation by traceable angle weighting method is proposed to improve the imaging capability of water column data.2.Aiming at the problems of strong noise,large amount of data,and difficulty in target recognition of water column image,a method of target extraction for two-dimensional water column image based on view conversion is proposed.Based on the statistical analysis of the characteristics of water column data from the direction and the vertical direction,the algorithm framwork is designed.The Otsu algorithm is used to split the beam array projection map for obtaining the image foreground area,and removing the water column background data.According to the mapping relationship of images from different perspectives,the sampling interval of the target and the seabed in the vertical map is located,and the local threshold is set for filtering one by one to achieve the purpose of suppressing the side lobes.The target area of the water column is identified by the convex closure calculation of the heading map.Experimental analysis shows that the algorithm in this paper can accurately locate the target area,ensures the processing efficiency of the water column image from the perspective of overall data,and has strong adaptability and controllability.3.Aiming at the uneven spatial distribution of surface sampling points in the three-dimensional modeling of water column objects,a three-dimensional reconstruction algorithm for underwater objects based on sequence contours is proposed.According to the acquisition principle of multi-beam water column data,the data are transformed into the geographical framework and the contour point cloud is extracted ping by ping.The methods of shifting the center of the contour line and dividing the spatial grid are used to avoid the problems of surface dislocation and self-intersection,and the triangular grid is constructed by using the shortest diagonal method.For the 'branch' problem between adjacent pings in the reconstruction process,the breakpoint is automatically inserted based on the Euclidean distance between the points,so that different contour lines correspond to each other.The results show that the algorithm can effectively reduce the redundancy of patches,avoid the phenomenon of holes,restore the characteristics of underwater objects.Compares with the existing ?-shape algorithm and the 'snow ball throwing' algorithm,the proposed algorithm has more advantages.4.Based on the characteristics and dynamic models of ocean internal waves,the influence of ocean internal waves on the accuracy of multi-beam bathymetry and the characteristics of seabed terrain distortion are analyzed.The effects of the internal wave in multi-beam bathymetry are analyzed from four dimensions of the vertical displacement of the sonic crust,the inclination angle of the sonic crust,the heading azimuth,and the depth of the seafloor,respectively.Aiming at the influence mechanism of different factors,the characteristics of seabed terrain changes and bathymetry error distribution under the influence of internal waves are analyzed,so as to accurately determine whether the measured seabed terrain is affected by internal waves.5.Aiming at the similar 'twist' folds anomaly in seabed topography affected by ocean internal waves,a method of ocean internal wave detection and synchronized bathymetry correction based on multi-beam water column images is proposed.Based on the characteristics of the water column image of the ocean internal wave and the distortion characteristics of the seabed terrain affected by the internal wave,the internal wave amplitude,wavelength,propagation direction and other parameters are extracted to construct the internal wave transient equation.According to the spatial geometrical relationship and Snell's law,the refraction path of the sound ray is determined,the three-dimensional sound line tracking is carried out,and the beam footprint coordinates are calculated.After several iterations,the accuracy of correction is gradually improved.Numerical simulations show that the algorithm can effectively improve the accuracy of multi-beam bathymetry,realize the detection of ocean internal waves and the correction of synchronous water depth,and improve the efficiency of multi-beam measurement.