Technique Of Bathymetric Artifact Elimination And Seafloor Footprint Positioning For Multibeam Bathymetry

Multibeam bathymetric technology is a high technology of contemporary seafloor topography surveying and one of major ocean investigating method, which has been widely applied in many areas of national defense and civilian use such as, hydrographic surveying, marine engineering, seabed resources exploration and development, etc, and has attracted high attention from more and more countries close to sea. Nowadays, the trend of development for multibeam bathymetric sonar is to achieve wide coverage measurement, high precision and high resolution and the integrated detection of seabed characteristics.To improve the validity and accuracy of wide coverage multibeam bathymetric data, the domestic and overseas researches are focusing on design of wide coverage acoustic sensor array, high-precision and joint estimation of DOA and TOA, the ensuring methods of the accuracy of depth measurement in outer beams, the elimination of bathymetric artifacts, the positioning of beam footprint point, the real-time monitoring of system, the editing processing of bathymetric data and other aspects. The dissertation considers the current development trend of relative technologies and the development theory and practical demand of domestic shallow-water wide-coverage multibeam bathymetric sonar, and mainly studies the three kinds of technologies, including the elimination of bathymetric artifacts, the positioning of beam footprint, the real-time monitoring of system. Specific contents include the following:First, the "tunnel effect" artifact in multibeam bathymetric sonar has been studied. Based on the analysis of the effect of "tunnel effect" on the results of depth measurement and its causes, the dissertation, from point of view on adaptive signal processing, studies sidelobe cancellation algorithm which can effectively restrain this artifact. RLS-Laguerre algorithm is proposed to eliminate the output of beam envelope, and GSC adaptive sidelobe canceller structure is applied to eliminating the complex output of beams. In order to realize GSC algorithm in real-time, SI-CG algorithm is realized and applied to eliminate "tunnel effect". In addition, relative algorithms have been realized by computer simulation, and used to process the experimental data on the lake, which proves its correctness and validity.Second, the bathymetric artifacts in multibeam bathymetric sonar arose by sound velocity and its elimination methods are studied. The dissertation points out that, because acoustic wave refracts when it propagates in inhomogeneous medium, the conventional computation model of constant sound velocity can bring in bathymetric artifacts to measurement results. Based on the assumption of the certain sound speed profile, the dissertation discusses the method of sound velocity correction, specifically including the correction algorithms and the processing flows in two sound speed profile models, layered constant velocity and layered constant velocity gradient models. And the process of experiment data verifies its effectiveness. Moreover, the bathymetric artifacts arose by surface sound velocity is studied. The modified formula of the error correction of steered receiving beam angle which is caused by the bias of surface sound velocity is derived. By the computer simulation, the dissertation quantitatively analyzes the influence of bias of surface sound velocity on steered receiving beam angle and depth. Then the method is applied to process the lake experiment data, and eliminate the bathymetric artifacts due to the error of sound velocity correction which leads to data mismatching between the adjacent survey lines.Third, dynamic beam footprint positioning, and installation and calibration technologies of multibeam bathymetric sonar are studied. Aiming at current insufficiency, the dissertation studies the dynamic positioning model of multibeam footprint by analyzing the relations of dynamic positioning error, device's installation parameters and ship's motion attitude, discussing multibeam sonar installation program and space coordinates system establishment and considering various factors that cause positioning errors. It studies the methods on positioning of beam footprint in array coordinates, and proposes a new positioning model to achieve precisely positioning in the condition of varying sound velocity. The dissertation studies the precise computing method of spatial coordinates and attitude of array in the geodetic coordinates, and positioning method and processing flow of multibeam footprint from array coordinates to geodetic coordinates. The processing results of the lake experiment data with the method is compared with the processing results of foreign commercial multibeam processing software Hypack to test accuracy, rigor and rationality of the positioning models in dynamic beam footprint positioning method proposed in the dissertation. Consider that the bias of array installation angle is difficult to measure directly, the dissertation studies and implements a dynamic calibration method of installation angle based on feature data processing, and uses lake experiment data to verify its effectiveness.Finally, in urgent need of independent development of domestic shallow-water wide-coverage multibeam bathymetric sonar, the dissertation further studies the technology of time synchronization and data time homing between multi-devices in process of multibeam bathymetry, the technology of real-time monitoring, and the technology of data editing, develops "real-time monitoring software" for high quality data acquisition and "interactive data processing software" that has the functions of multibeam data homing, automatic and manual combined fast outlier data elimination, etc., assesses the working performance of domestic shallow water wide coverage multibeam bathymetry sonar by several times of lake experiments, and verifies practicability and effectiveness of the "real-time monitoring software" and the "interactive data processing software".