Report of Hydrographic Researches
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Effect of SLR Data Obtained at Simosato Hydrographic Observatory on the Orbit Determination of TOPEX/Poseidon (in Japanese)
Horizontal Motion of Chichijima Derived from Satellite Laser Ranging Observations
Observation of 1994 November 3 Total Solar Eclipse
Thermal Distribution and Chemical Compositions of Discolored Waters Derived from Submarine Volcanic Activities (in Japanese)
Inertial Motion Detected by Satellite-Tracked Surface Drifter (in Japanese)
Making of 'Seafloor' Stereograph from Side-looking Sonar Imagery and Swath Bathymetry (in Japanese)
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Effect of SLR Data Obtained at Simosato Hydrographic Observatory on the Orbit Determination of TOPEX/Poseidon
The effect of SLR data of Simosato Hydrographic Observatory on the orbit determination of TOPEX/Poseidon (T/P) was investigated by comparing orbits calculated with and without Simosato data. The orbit of T/P was calculated by using GEODYN-II, which is an orbit analysis software used for orbit determination of T/P at NASA Goddard Space Flight Center. The accuracy of resulting orbit solution is about 3 [cm] RMS in radial direction. By the presence of Simosato data, the spheroidal height of T/P differs by 1-4 [cm]. The difference becomes largest at the vicinity of the observation period at Simosato and appears for about one day before and after it. This result suggests that the effect of Simosato data appears not only above Japan but also on the whole orbit of T/P.( Text is Japanese )
The horizontal velocity of Chichijima was obtained through the Satellite Laser Ranging (SLR) campaign observations carried out in 1988 and 1996 by the Hydrographic Department of Japan. SLR analyses were made with global data by combining multiple geodetic satellites, AJISAI, LAGEOS-I and -II. The velocity of Chichijima from the SLR positioning results was estimated both in local and global approaches: from the baseline change rate with Simosato, the permanent SLR station in Japan, and from arc length rates between global stations. The latter approach gave an absolute velocity of Chichijima based on the no net rotation system. Both results are consistent with the predicted values from the Philippine Sea plate motion model by Seno et al. (1993) obtained from the seismic slip vectors along the plate boundary. The result also agrees with those from other space geodetic techniques, VLBI and GPS observations.
Key words : Chichijima, SLR, Philippine Sea plate, plate motion, no net rotation system
Observation of the total solar eclipse on November 3, 1994, was made by the Hydrographic Department of Japan (JHD) by means of flash spectrum recording method. Analysis of the observation gives the following correction to the relative position and semidiameter of the Sun and the Moon to be applied to the tabular values in Japanese ephemeris:
Key words: Total solar eclipse, contact times, ephemerides of the Sun and the Moon.
Thermal Distribution and Chemical Compositions of Discolored Waters Derived from Submarine Volcanic Activities
The Hydrographic Department actively participates in the national programme for prediction of volcanic eruption since the beginning of this programme in 1973.
This paper shows a review of the analytical results of thermal distribution and chemical compositions of several volcanic discolored waters observed and collected by the Hydrographic Department.
Thermal distribution of discolored water by the airborne thermal infrared radiometer makes clear the complicated thermal distribution pattern around the spouting point of the Kaitoku Seamount and the Hukutoku-Oka-no-Ba submarine volcanoes .
Relative temperature differences between the sea surface temperature and the volcanic discolored water temperature are in harmony with the submarine volcanic activities.
Total Fe is decreasing and pH value is increasing according to the distance from the spouting point of volcanic discolored water.
Triangular diagram on Fe-Al-Si and/or (Fe+Al)/Si from chemical analysis of volcanic discolored waters indicate the degree of submarine volcanic activities and make possible to compare about volcanic activities of submarine volcanoes in different time and/or at different places.( Text is Japanese )
From late October to middle November in 1981, trajectory of the ARGOS surface drifter which flowed in the sea area 41-39 N east off Japan depicted continuously anticyclonic trochoidal loops. Twenty one loops, which were mostly circular, were found in the period from 25 October to 11 November with the average period of 18.8 hours. This clearly shows the existence of inertial motions in the studied area. The mean flow was calculated to be 10-25 cm/sec southwest ward from 18-19 hours running averaged locations from interpolated locations of the drifter at every one hour. Using above results, the speed of inertial motion was estimated as 45-80 cm/sec. Time change of speed and radius of inertial circular flow tend to decrease as a whole, respectively, with several intermittent increases. It is suggested that these intermittent reinforcement are generated by strong wind blow on the sea surface at every 3-5 days.( Text is Japanese )
High resolution side-looking sonar data is of immense use in understanding the geology and the tectonics of seafloor. In order to study the detailed morphology and the crustal movement inferred from the topographic fabrics, it is necessary to analyze bathymetry as well as backscatter data. We introduce a new method 'seafloor stereograph' to combine two datasets, side-looking sonar imagery and multi-beam bathymetry. 'Seafloor stereograph' consists of two side-looking sonar images from slightly different viewpoints. It helps intuitive and rapid understanding of the seafloor and gives us new information and interpretations, which have not been obtained from the usual analyses. Two examples of 'seafloor stereograph' are presented, which lead us new interpretation of the studied area. 'Seafloor stereograph' has proved to be of great help in deciphering folds, faults and sediment structure etc. It will become powerful tool for morphological and geological analysis and for the study of seafloor tectonics.
Keywords: Stereograph, Side-looking Sonar, IZANAGI, Multibeam Bathymetry, Crustal Movement( Text is Japanese )
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