In recent years, Hydrographic surveying is undergoing fundamental change in measurement technology.Especially, Narrow multibeam surveying system is developping rapidly. So, IHO(International Hydrographic Organization) standards for hydrographic surveys:4th Edition, 1998. Then the authorities concemed are required for this new standard. In a field of Port and Airport construction, Narrow multibeam surveying systems are active part for manegement in construction in the second phase project for the Kansai International Airport andthe government body and port management bodies are beginning to use this systems positively in Japan. So, I have made literature investigating, hearing for persons concerned and field working for underwater mesurement.
　The following results were obtained by this study.
1. IHO standards for hydrographic survey :4th Edition,1988,then Harbours ,berthing areas ,and associated critical channels with minimum underkeel clearances have to be explicitly designated by the agency responsible for survey quality. It must be ensured that cubic features greater then lm can be discerned by the sounding equipment. So, the need of Narrow multibeam surveying systems are increased.
2. In the second phase project for Kansai International Airport, the Narrow multibeam surveying systems are adopted (In the first phase,this systems are not used) after accuracy confirmation investigation were executed, especially ,the edge side accuracy confirmation investigation are examined closely. So, accuracy of beam edge side were made clear. And this systems are used on the basis of this investigation.
3. At Present, Narrow multibeam Sonars which are made practical for survey seabed,and judged we can use port and harbor surveying in Japan by trader hearing,are made by 3makers,6kinds.
4. By trader hearing, The definition and test method of sounding accuracy are different by makers. A conscientious maker open good accuracy result as official result when there are two result by depth.
The greatest subject of this system is collecting survey accuracy results rapidly.
5. The most suitable ship speed for underwater mesurement at a depth of 15m is 6kt or less almost all.