Report of Hydrographic And Oceanographic Researches
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Original Papers
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Admiralty Charts for Adjacent Seas of Japan in the last Days of Tokugawa Regime and early in Meiji Era
, p.1 -
Bias estimation of acoustic transducer position for seafloor geodetic observation
, p.17 -
Acoustic phase characteristics and phase centers of the acoustic transducers for seafloor geodetic observation
, p.29 -
Newly developed methods for SLR observation at Simosato Hydrographic Observatory
, p.37 -
Development of Bias error Correcting Methods for Ocean Current Velocity Measurement by Using Electromagnetic Log with Dual-axis Sensors
, p.45
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Abstracts
Admiralty Charts for Adjacent Seas of Japan in the last Days of Tokugawa Regime and early in Meiji Era
Japanese Government made ¡ÆAn Peace and Amity Treat£ù between Japan and the U. S.¡Ç in 1854 after long national isolation, to permit foreign ships¡Ç calling at harbors for water, supply and coal. Japanese Islands are located at one of the end of the ocean route between the U. S. A. and China traversing the North Pacific Ocean. Surveys along the routes were carried out to publish charts of ¡ÆStrait of Tsugar¡Ç and only a few harbor plans and to maintain small-scale charts particularly rectifying coastlines of offshore islands in the Sea of Japan. Since amity and commercial treaties are concluded in 1858, surveys in Japanese coastal waters are carried out in earnest and large-scale charts are increasing rapidly. At that time the British Admiralty Chart had confidence of mariners in Western countries, because of its quality and the publishing policy to cover all navigational waters for trading ships. This note shows outline of navigational charts in Japanese waters, published in the last days of the Tokugawa Regime and early Meiji era before the establishment of Japan Hydrographic Department in 1971 and the brief history of the Admiralty Chart during contemporary period.
Although all of hydrographic surveys in this period were operated by foreign survey vessels, maps made by Japanese land surveyors contributed toward the preparing navigational charts, required by trading ships, in due course. This note also describes the adoption of data from the Japanese maps into the navigational charts during the above-mentioned period.
Bias estimation of acoustic transducer position for seafloor geodetic observation
Among results of JCG's intensive observation off Miyagi Prefecture, some epochs gave erroneous solutions presumably caused by the bias of acoustic transducer position. We tried simultaneous estimation of the bias of acoustic transducer installation and positions of the seafloor reference points. As a result, we detected significant biases dependent upon difference of used devices i.e. acoustic transducers, observation poles, etc. Correction for these biases gave less scattered time-series of determined positions and reduced residuals of traveltime. This method took effect to improve the accuracy of position estimation of seafloor reference points.
Acoustic phase characteristics and phase centers of the acoustic transducers for seafloor geodetic observation
Institute of Industrial Science, University of Tokyo and Hydrographic and Oceanographic Department, Japan Coast Guard have been conducting seafloor geodetic observations since 2000. Sufficient observational results to discus the system and the observational method have been established as we accumulated the experiences of the observations. Issues and knowledge that we have through the observations should be fed back to the system and further observation for improvement. One of such issues is one inherent in acoustic transducers for acoustic ranging. Ranging errors were caused by the operational principles of the transducers and the reference point set on the point at the top center of the transducers. In order to take measure to this issue, tank tests were conducted to evaluate the ranging characteristic curves of the acoustic transducers. And then the acoustic phase centers of the transducers were deduced from these curves. The comparison of the acoustic phase centers of two types of the acoustic transducers, that is, the cylindrical and the spherical curved disk transducers should be needed to retain the continuity of the long-term seafloor geodetic observation.
Newly developed methods for SLR observation at Simosato Hydrographic Observatory
In satellite laser ranging (SLR) observation the distance to an artificial satellite is measured from round-trip travel time of a laser pulse which is transmitted from the station, reflected at the corner cube reflectors on the surface of the satellite and then received back at the station. The ranging accuracy depends on how accurately the specific point of returned pulse is identified. A simple method to identify such a point by detecting the leading edge of a transmitted and a received pulse has been degrading the ranging accuracy because of 'time walk' caused by variation of signal intensity. In order to reduce the time walk, two new techniques were introduced at Simosato Hydrographic Observatory in 2006: namely, the methods named Triple Threshold Screening (TTS) and Constant Mid-signal Detection (CMD). The authors intend to verify both of them are effective in improvement of ranging accuracy in this paper. The principle of these techniques and some examples of their effectiveness are given.
Development of Bias error Correcting Methods for Ocean Current Velocity Measurement by Using Electromagnetic Log with Dual-axis Sensors
The trajectory prediction of drifting matter is always important for rescue operations on the sea.
The ocean current for the prediction is usually observed by ADCP equipped on vessels of Japan Coast Guard. Recently a newly built high-speed vessel is equipped with an electromagnetic log with dual-axis sensors (2EM log) taking the place of ADCP, not to spoil its navigational capability.
So we were required the evaluation of the ocean current observed by 2EM log and the development of processing methods for it. As the results of sea trials, we found a conspicuous bias error included in the ocean current. The bias error includes misalignment error and scale error, which are also contained in the ocean current observed by ADCP. Although the data bias error correcting method to reduce bias error is basically the same with the methods for ADCP data, dataset of correction for bias error should prepared for each vessel in various vessel-speeds. This paper shows a solution method to determine the dataset, named 'Random Cruising Method'.
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