The Narrow Multi-Beam Echo Sounder for Shallow Sea Use (Hydrochart II) was introduced to the survey ship "Ten-yo" of the Hydrographic Department, M. S. A. in 1986. It is an excellent system which is able to survey the sea floor in swath widths 2.5 times the water depth.
In the shallow sea, the high accuracy of 30 cm is required for producing safe navigation chart. However the data processing and calibration techniques with this echo sounder for nautical chart haven't yet to be established. NOS(NOAA, USA) has a similar system and is also interested in this problem.
The writer has studied following four themes about the data processing methods of Hydrochart II by refering the methods of NOS.
(1) Data accuracy
(2) Methods for eliminating erroneous data
(3) Methods for making bathymetric charts as the original sheet of the nautical chart
(4) Checking the reliability of the bathymetric chart with the contour chart
In this paper, the foregoing themes are discussed and the results of the investigation suggest that the prospect for using Hydrochart II to make high-accuracy nautical charts is bright.