Analysis And Removal Technology Of MultiBeam Bathymetric Artifacts Arosed By Ray Refraction

MultiBeam Bathymetric System is one of the most advanced and effective hydrographic instruments in the hydrographic survying, people do a lot of detailed research on the precision of multibeam sounding data and influenced factors, and ray refraction has been found as an important influenced factor in the bathymetric accuracy(especially in the marginal beams). If we can't get the accurate sound speed profiles, the variances of the sound speed profiles(ssps) will influence the survying precision, and resulting in the distortion of submarine topography.The aim of this article is to analyze the bathymetric artifacts and eliminate the artifacts arosed by refraction. Specifically, we describe the basic physics of sound propagation, the characteristics of its propagation in seawater, and how refraction affects echo sounding and what is usually done to reduce the degradation, doing researches mainly on the depths computing with methods of average sound speed and ray tracking. However, the traditional methods of acoustic velocity correction can not depart from the knowledge about the existing ssps. In most cases, it is difficult to get more accurate ssps in post-processing. The final part of the thesis is devoted to the methodology, application and results of the new refraction correction method called crossing check. This method is based on the regulation of crossing survey and allows automated adjustments of the bathymetric artifacts present in multibeam datasets. These adjustments are based on the assumption that the center depths of the survey lines are adequate to be used as references for the computation of corrections. The application of this method can make the depth data of the lines more close to that resulted from the center beams of the check lines, at last, this method complete the depth correction of the other beams.