High precision survey by the multibeam sonar in the dam site

In these days when the demand of the water resources for the industry, the agriculture, drink, and so on, is increased, it has a very important meaning to observe the passing year change with correct dam pondage from the viewpoint which operates a dam appropriately. Therefore, the multibeam sonar system which is used by the hydrographic survey and so on is useful for surveying correctly, but this method has some problems according to the landform situation in the dam site: for example, because the dam is often located in the V shape gorge, the sight to the GPS satellite is bad. With approaching a shore, the sight to the GPS satellite is worse. We made a research of the technique development to evaluate water depth errors and to improve accuracy of survey, in order to measure the pondage of the dam with the high-precision with the multibeam sonar system. The research to introduce here was carried out in the dam site, but it is expected that this technique will be effective in a place where the signal from the GPS doesn´t reach easily like a narrow cove and a fiord surrounded by mountains. As the specific research issue, we narrowed down to three problems. The first has expanded a useful area of KGPS by a method of two dimensional processing. Secondarily, the motion difference of an underwater sonar head and a ship body was compared. At last, the comparative test of a magnetic compass (KVH Gyro-track) and a fiber-optic gyro (OCTANS) was carried out to investigate the necessity of the high-precision acoustic beam position measurement that used a fiber-optic gyro. As a result, detailed bathymetric information of the lake was got.