| With the needs of the development of marine surveying technology, it's very urgent to solve the problem which the depth datum is discontinuous. Studies on seamless vertical datum have been carried out around the world. In some maritime countries, their own seamless vertical datum has successfully been set up. At present, some related foundation works on the local marine seamless vertical datum have been done in China. But which also have many problems to be solved, for example, it has not been thorough enough understanding of the importance of building China's unified seamless vertical datum. Funded by the Special Grand National Project (908-ZC-I-07), Chinese National Programs for High Technology Research and Development (863 Program) (2009AA121402) and other related projects, a systemic analysis and research has been made for several methods about seamless vertical datum. This thesis consists of seven chapters. The main contents are as follows:1. According to international seamless vertical datum definition, by deeply analyzing the definition, properties, characteristics, realization and application status of the existing tidal face, geoids,1985 national vertical datum and ellipsoid, and by referring to the international experience, it is proposed that CGCS 2000 ellipsoid would be used as our country unified seamless vertical datum.2. The method to build mean sea level modeling is studied. Based on the principle of satellite altimetry, the application in the ocean field was analyzed. By means of satellite altimetry data to build Bohai Sea mean sea level grid modeling and converted reference ellipsoid to make reference datum to be seamless vertical datum (CGCS 2000). But the data obtained by satellite altimetry has big error in offshore area and shallow water area. Grid model was corrected locally by using five points which have a long-term tidal observations and GPS data points. Experimental results showed that the correction make the two corrected points model difference reduce from -2.283m to -0.805m and 2.023m to 0.545m respectively. Therefore, a single point precision in gird modeling has improved significantly. Curved surface approximation was made by using fitting methods. Combining the characteristics of Bohai sea data with the analysis of several basic surface fitting methods, Bohai Sea mean sea level modeling was built by Kriging fitting method which is one of semivariogram function Exponential-Cosine (type 1). The root-mean-squared error is 6.42 cm. The external precision ws 99.93% and RMS error was 13.46 cm.3. The methods to build depth datum modeling were studied. Using Bohai depth datum grid modeling resolved by POM mode and choosing Kriging fitting methods which was one of semivariogram function Exponential-Bessel, Bohai Sea continuous seamless vertical datum was obtained. The relative RMS error was 1.16 cm. In addition, it is found that the characteristic of this model was in agreement with the results calculated by real tidal data.4. The method to build separation model was studied. The "Model Difference Method" was proposed. By using the relationship between mean sea level and depth datum, Bohai Sea separation model was built and the error was analyzed.5. Conversion method based on the vertical datum was put forward. Namely through the establishment of seamless vertical datum, the land vertical datum and ocean vertical datum was unified to simplify transformation between orthometric height (or normal height) and chart height and map splicing. Some single beam sounding data in a certain area of Bohai Sea were used to do conversion tests. The experimental results showed that the conversion method was technically feasible.
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