| Water transport is an important part of the national transportation network and the Yangtze River is the major river transportation of our country. As the basis for the construction and maintenance of waterways, the importance of the channel mapping work has become increasingly highlights. Compared with the traditional method which has tidal observation, hydrographic surveying without tidal observation weakens artificial interference factors, improves the reliability of the outcome, reduces the investment and the cost of maintaining the tidal stations, and saves the expense of human and financial resources. Based on the existing equipment, secondary development and building of a complete hydrographic surveying without tidal observation system based on network RTK was done. Program test and accuracy assessment were taken in a typical on the Yangtze River, then the data were analyzed and compared with the traditional method which has tidal observation. The main contents and results of this paper are summarized as follows:(1) A detailed introduction of the importance of the Jiangsu section of the Yangtze River water depth measurement has been done. First, the development of hydrographic surveying and positioning means were described, and then the development and current situation of local resembling geoid based was analyzed and discussed. The last part was the detailed description of the composition and positioning principle of network RTK positioning system based on the JSCORS and the principle of hydrographic surveying without tidal observation.(2) Based on the existing equipment, secondary development and building of a complete hydrographic surveying without tidal observation system based on network RTK was done. Details of the procedure of the system including field data collection and data processing were making. The system involves the height datum conversion. Three elevation fitting model were analyzed and compared. Taking the characteristics of the terrain and the trend of the Yangtze River in Jiangsu section into account, this paper used the method of conicoid fitting with the method of BP neural network.(3) The error sources of hydrographic surveying without tidal observation system constructed in this paper were deeply analyzed. There are WGS84 high error measured by network RTK, error of resembling geoid, the transducer deviation and the hull tilt, and sounding delay effect. The accuracy that outer coincidence of plane positioning is better than 3cm and the elevation is better than 5cm of JSCORS positioning system was tested and verified through experiments. The method of subsection conicoid fitting with the method of BP neural network was used to fit the elevation model. The inner precision index is±1.84cm; external accord accuracy index is±1.95cm. Also using existing control point data to test the external precision of the model, the height conversion accuracy is 3.95cm. The elevation fitting model in this article which has a good overall accuracy is proved, which can meet the water level accuracy that less than 10cm of hydrographic surveying without Tidal observation.(4) Specific experimental programs have been designed to collect data in a typical river on Yangtze River. Data processing and analysis was done to test the accuracy of hydrographic surveying without tidal observation system. How to get the water level of without tidal observation and obtain underwater elevation process by method of without/with tidal observation are detailed. Compared with the tidal water level, the water level of without tidal observation is in the difference of 15cm, with an average of 6.6cm. Jitter range of the underwater elevation difference is about 25cm, with an average of 7.6cm, which meets waterway engineering surveying specification that less than 20cm. The results of without/with tidal observation are consistent. The conclusion that the hydrographic surveying without tidal observation system in this paper can be promoted and applied in inland waterways is put forward. |
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