Research On Post-evaluation Method Of Multibeam Sounding Quality

The multibeam sounding system is one of the main equipment in Bathymetric survey.Because of the dynamic working environment and the characteristics of multisensor combination,the sounding data will be affected by a variety of error sources.In order to ensure the reliability of multibeam sounding data,it is necessary to evaluate its quality by some methods.In this paper,we focuses on the post-evaluation method of multibeam sounding quality,analyze the error sources in the process of multibeam sounding in detail,and summarize the related specification requirements of multibeam sounding and the commonly used post-evaluation method of multibeam sounding quality.Aiming at the complicated situation of post-evaluation of multibeam sounding quality in the depth discrepancy calculation,the calculation process and method of the depth discrepancy are deeply studied.Aiming at the problem that the common HGM(Hare Godin Mayer)method has deviation due to approximation or simplification in the calculation of uncertainty,a precise calculation method for multibeam sounding uncertainty is proposed.The specific work is as follows:(1)A method for calculating the depth discrepancy of overlapping line-surface is proposed and compared with the commonly used method.In this paper,we deeply studied the calculation process of the depth discrepancy,and summarized three commonly used methods of the depth discrepancy calculation:discrete point method,point-surface overlay method and surface overlay method.On this basis,considering the characteristics of high accuracy at the central beam and low accuracy at the edge beam in multibeam sounding.A method for calculating the depth discrepancy of overlapping line-surface is proposed,which is helpful to reflect the difference of bathymetric accuracy between the central beam and the edge beam,and to discover in time the errors of sound velocity and roll correction in the data results.Finally,the calculation results of the depth discrepancy of the four methods are compared with the measured data,and the advantages,disadvantages and application of each method are illustrated.(2)Based on the existing research results,the calculation process of a accurate reduction model of footprints is derived in detail.In this paper,on the basis of the accurate reduction model of footprints,we calculates the precise three-dimensional incident angle of the beam by synthesizing the information of the beam steering angle,the installation deviation angle of the transducer and the instantaneous attitude angle.According to the process of the sound ray tracing,dynamic eccentricity correction,dynamic delay correction and coordinate reduction,the formulas for calculating the accurate reduction model of footprints are obtained.Comparing with the common reduction model of footprints,the accurate reduction model of footprints uses the precise three-dimensional incident angle of the beam to track the sound line,and calculates more accurately the effect of the sound line bending on the process of footprints reduction,and improving the sounding accuracy.(3)A method for calculating the uncertainty of multibeam sounding points based on a accurate reduction model of footprints is proposed.This paper analyzes the error sources in multibeam sounding.Based on the law of error propagation and the accurate reduction model of footprint,the error propagation of each error source in each phase of beam reduction is deduced in detail,And the accurate uncertainty model of multibeam sounding results is proposed.Compared with the common HGM method,the accurate uncertainty model of multibeam sounding considers the effects of installation deviation angle error,representative error of sound velocity profile and error propagation in sound ray tracking,so that the calculation process is more rigorous and accurate.In order to further verify the feasibility of the proposed method,the calculated results of the two methods are compared and analyzed by using the measured data.