Study On The Processing Of Echo Sounding Data And Combination Of Bathymetric And Topographic Data

In this dissertation based on the law of transmission of sound wave in bathymetric survey, the anti-interference techniques used in acquisition of sounding are given, and the performance of echo sounders with its transducer are discussed. Using the algorithms of changing the calculation region interpolating comparison test with iterative weights based on robust M-estimation, the blunders of sounding data are detected and eliminated. According to the maximum allowable error of sounding in the standards for hydrographic surveys, the error model of Single-beam Echo Sounders(SBES) and Multibeam Echosounders(MBES) are analysed respectively and a crosscheck method based on ping is put forward to evaluate the quality of sounding data. In order to solve the problem of inconsistencies between the data in separate reference datums, different data format and variety of representing the same object, etc, a project of blending multi-source bathymetric/topographic data seamlessly is designed. Based on a common datum established by the methods of transforming horizontal coordinate and interpolating vertical datums, a seamless DEM derived from discrete depths and terrain contours is combined, and a algorithms for simplifying DEM based on point deletion is used to represent DEM in different scale. The main research contents and achievements are as follows:(1) According to the law of transmission of sound wave in the sea, the performance of echo sounders is analysed by the basic parameter such as frequency, band width and pulse length. The development of echo sounders and the capability of transducer with its application in practice are specified. Based on the relationship between the performance of transducer with its beam width, the transducer beam torsion and beam lobe reduction using shading functions are discussed. According to the relationship between the coverage of transducer with beam pointing angle, beam width, depth and mean slope of the seafloor, the relationship between the coverage of the seafloor with dimension of the ensonified areas, beam spacing across track, ping rate, ship's speed, yaw,pitch and roll are studied. The characteristic of MBES signal, the method of amplitude detection for central beam and of phase detection for edge beam are specified. Based on the analysis of common inner and outer interference in acquisition of sounding, the methods of restraining and weakening interference are studied and various techniques of anti-interference used in echo sounding are brought forward. (2) In order to improve the way of manual blunders detection currently, the character and shortage of algorithms of automatic blunders detection, such as entrance restrict filter, Slope algorithms, curve surface imitation, robust estimation, are discussed, and the algorithm of changing the calculation region interpolating comparison test with iterative weights based on robust M-estimation is suggested. Experimental results indicate that the algorithm is effective to eliminate adjacent blunders, especially for cluster blunders. Based on the classification of hydrography and the Minimum Standards of error in sounding, the error resulting from position system, transducer draft, sound velocity correction, seafloor slope, sea wave, tide correction and vessel attitude are discussed for SBES and MBES respectively.(3) In order to evaluate accuracy of sounding data by the intersection discrepancies of main lines and check lines, the algorithm of computing intersection for digital sounding dada is studied. For the limitation of crosscheck algorithm based on points and plane for MBES data, the algorithm of crosscheck based on ping is studied. The comparison of two algorithms in practical test shows that latter is more accurate in evaluating the quality of MBES data and can distinguish the type of errors.(4) A project of blending multi-source bathymetric/topographic data seamlessly is designed to solve the problem of inconsistencies between the data in separate reference datums, different data format and variety of representing the same object, etc. Based on a common datum established by the methods of transforming horizontal coordinate and interpolating vertical datums, a seamless DEM derived from discrete depths and terrain contours is combined, and for the problem of representing slowly for processing mass sounding data, a algorithms for simplifying DEM based on point deletion is used to represent DEM in different scale and its validity is proved by practical test. For the demand of cooperated map of army, navy and airforce in amphibious warfare, the soundings, topographic data, islands, features and military vector chart data are integrated. Experimental results indicate that the project can seamlessly blend multi-source coastal zone data and realize three-dimensional representation in multi-scale.