From comparisons of SASS-derived winds with surface truth in the range of low wind speed, it has been indicated that more studies were needed to resolve the characteristics of capillary waves on the water surface microlayer. For the above reason, a new method for measuring surface tension and viscosity of the layer, based on the properties of capillary waves, was developed as following view points; 1) surface buoy composed of water surface film sampler and reserving box, 2) wave channel equipment for taking photographs of Moiré fringes, and 3) Moiré method to analyze amplitudes and lengths of capillary waves. Firstly, the new capillary wave method was applied to top water instead of distilled water to check the accuracy, and the satisfactory accuracy was indicated for the optimum wave frequency of 30Hz-70Hz. Nextly, the present method was applied to sea water off the Sagami River mouth. In this paper we would show that more reasonable results than conventional analyzers are given by the capillary wave method.
Data obtained in wave-tank experiments usually exhibit considerable scatter, which seems to arise mostly from inaccurate movement of paddle of wave-maker or its unintensional change among experimental runs. By using stepping motor, ball-screw. linear-slider, and personal computor, we constructed a digitally controlled wave-maker for a small-scale laboratory water tank. The wave-maker is controlled unidirectionally and no feedback system is applied in the present stage. Reproducibility of generated wave forms is remarkably good even without feedback system. Demonstration is made for the successful application to solitary wave experiments.
GPS drifting buoy system was developed to measure precisely the currents in coastal or bay area. This system consists of two drifting buoys equipped with GPS receivers and land-based station. The technical problems were investigated and solved in the research measurements off the estuary of Fuji River at the innermost of Suruga Bay. The tracking of the GPS drifting buoy was proved different from the currents at the drogue suspended down 30 m deep. This may be caused of current changes with depth. The performance of the GPS drifting buoy system was tested in Nakagusuku Bay of Okinawa Island during 10/18-10/24/1991. This bay is almost surrounded with cays and coral reefs. The drogue was suspended down 5 m deep in this research. The wind blew from the northeast through the research period. The GPS drifting buoys were carried along the direction of the wind and drifted to-and-fro with the tide. The currentmeter suspended down 5 m from the buoy showed that the buoy moved almost together with the currents caused of wind and tide.
Seafloor depth measurement technology has been changing recently from "individual soundings along the ships track" using single beam echo sounders to "swath-mapping" using multi-narrow beam echo sounder (MNBE) with the cross-fan beam techniques. This enables detection of the sea-bottom in topography the form of wide swath perpendicular to the ships track. We have developed the MNBE HS-500 II which uses a frequency of 500 kHz to detect sea-bottom depths to 50 m. Its main advantage is its ability to detect sea-bottom depths over a 90 degree swath angle at a transmission repetition rate of 2 times/sec resulting in a 1 degree resolution. Bathymetric data collectd by the HS-500 II is stored on tape along with ship heading and position that are sent from external sensors. We will also introduce a software package that we have developed along with the HS-500 II, which permits the off-line use of a personal computer to produce bathymetric charts covering wide areas seafloor from the stored data.
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.