The Hydrographic Department of Japan has constructed the "Depth data file" for the past several years. Attributes and locations of the point-and line-information included in the nautical chart are numerized and put into the complete chart data base. The point-information includes the depth, the quality of bottom material and so on, and on the other hand, there are the coast line, the contour line and the others in the line-information. For numerizing a mount of chart data precisely and efficiently, we need some degitizing systems such as scanner and degitizer. Firstly, by using scanner, the accurate information of locations are able to be taken from a mount of chart data. Nextly, by using degitizer, locations are repaired and attributes are put for these data. We applied the computer mapping technique in Urban Information System developed by our corporation to this degitizing process. On this paper, I will explain how the data files can be constructed more efficiently, in the present processing.
The Manned Submersible Vehicle is presently performing very important mission in the observation of the sea bed. However, it cannot accommodate the many specialists who would like to conduct their own observations. If such specialists could be supplied with picture of the sea bed in real time, the submersible would be more effective aid for geologists, biologists and other researchers. But it is not real time information for scientists on support ship. We are carring out system development of long-distance picture transmission by acoustic signal. After many experiments at the acoustic tank, we have successfully carried out ocean experiment of acoustic transmission of colour pictures from the depth of 3,500 m to the surface. In this paper, the development process and the results of many experiments of this system are descrilad.
Recently, development of ROV (Remotely Operated Vehicle) and their related activities have been abruptly advanced. Total numbers of tethered self-propelled ROVs were beyond 1,200 in the world and 120 in Japan. About 96% of ROVs in Japan are small ROVs, depth rated between 100m to 500m. Those small ROVs are easily operated from small fishing boats or small ships of opportunity, therefore chance of observation of sea bottom is provided more easily before few years ago. But those ROVs have also limitations in their speed and periferal gears such as acoustic navigation system. Most of them are very difficult to operate under current condition beyond 1 knot and to determine precise position. We have been developed small ROVs and used for bottom surveys since 1980. This paper describes a examples of bottom surveys using small ROVs their limitation. This paper also describes about an example of deep sea survey by a large deep submergence (3,300m) ROV "DOLPHIN-3K" and it's performance.
GPS, a satellite positioning system being developed by the United States, has been used by the private sector from the test phase and vessels which are equipped with GPS receivers are in creasing. GPS is a system to determine the position of the receiver by knowing the distances from the satellites to the receiver, as the arrival time of the signals which are composed by the satellites are measured with the receiver clock. GPS is expected to enter into the operational phase in a few years. In addition to the single positioning, many applications by using GPS such as translocation method have been studied. More than two receivers are used simultaneously in the translocation method and the relative position of one receiver is determined precisely referring to the other receiver. In this method, common part of errors in determining receiver clock face and in the orbital elements of satellites etc. are removed by the simultaneous observation, thus attaining high precision of the relative positioning. A study to develop receivers to obtain precise relative positioning of moving stations, especially vessels, referred to a known point by using the translocation method has been carried out. The principle of this method and the result of the test observation obtained so far are reported in this article.
The Japan Meteorological Agency developed the ocean acoustic tomography system from 1983 through 1988 under the financial support of the Science and Technology Agency of Japan. In this stud y, acoustic source and receiver were developed and tested in the open ocean. The transmit frequency of this acoustic source was 400 Hz including the phase modulation which was a 127-digit maximal length shift register sequence. Sound signal with 31.25-ms resolution was transmitted at 20-min intervals for a 5-day period between the acoustic source and receiver moored at 1580 m and 1480 m depth, respectively. The arrival time structure of the multipath field for an interval of 108 km betweem source and receiver was clearly obtained by cross-correlating the coherently averaged in coming signal with a stored replica of the transmitted signal.
An acoustic doppler current profiler (ADCP) remotely measures vertical profiles of horizontal and vertical water currents from a moving vessel. In this paper, this instrument is applied for visualizing the flow in coastal waters. Some practical informations about using ADCP in coastal waters are given with some examples of observations. A method of analysing the ADCP data is presented. A comparison between numerically calculated flow pattern and ADCP data is conducted, and it is shown that ADCP data provide an excellent basis for evaluating fine-mesh numerical models of coastal circulations.