Journal of the Geodetic Society of Japan
Online ISSN : 2185-517X
Print ISSN : 0038-0830
ISSN-L : 0038-0830
Volume 55, Issue 1
Displaying 1-8 of 8 articles from this issue
MEMORIAL PAPERS FOR THE TSUBOI PRIZE
  • Masayuki Fujita
    2009 Volume 55 Issue 1 Pages 1-15
    Published: 2009
    Released on J-STAGE: January 31, 2012
    JOURNAL FREE ACCESS
    This paper mainly summarizes the efforts made on the development of the GPS/Acoustic seafloor geodetic observation technique carried out by the Japan Coast Guard, especially the way of tackling various error sources in the data analysis procedure to attain the precision of centimeters level. The principal errors in this technique arise from the long baseline condition for the kinematic GPS and acoustic velocity structure in seawater for the undersea positioning. The former was minimized by applying the software properly treating the spatial inhomogenuity in the troposphere and ionosphere together with considering various operational conditions based on the height assessment of positioning results. The latter is more specific to this technique and was resolved through numerical estimation of errors along with the development of the undersea positioning algorithm. After tremendous efforts for improving the precision including above, we had successfully detected the intraplate seafloor movement associated with the oceanic plate subduction off Miyagi Prefecture in 2004, for the first time in Japan. Remarkable results have followed since then with the precision and its stability improved. The paper also touches upon the author’s other contributions to the marine geodesy fields: those relevant to the establishment of the marine geodetic control network by JCG using the SLR technique and also to the discussion of oceanic effects on the earth rotation variation through the torque approach.
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  • Yoshinori Shoji, Tetsuya Iwabuchi, Yuki Hatanaka, Hiromu Seko, Ryuichi ...
    2009 Volume 55 Issue 1 Pages 17-38
    Published: 2009
    Released on J-STAGE: January 31, 2012
    JOURNAL FREE ACCESS
    The Global Positioning System was developed during 1970-80 in the United States. In 1994, The Geographical Survey Institute (GSI) of Japan began partial services of the nationwide GPS network named GEONET (GPS Earth Observation NETwork). Prior to the start of the GEONET service, Japanese geodesists and meteorologists held the first workshop on “GPS Tropospheric Delay” at the National Astronomical Observatory Mizusawa and recognized the importance of GPS meteorology with a suggestion of N. Mannoji from the Japan Meteorological Agency (JMA). After one year feasibility study based on a concept proposed by H. Tsuji of GSI, Japanese GPS meteorology project “GPS/MET JAPAN” was launched in 1997. This five year project from April 1997 to March 2002 was aiming at two birds with one stone; an application of precipitable water vapor (PWV) from the GEONET to data assimilation system in numerical weather predictions (NWP), and an improvement of geodetic accuracy of GPS based on NWP data. At the dawn of the project, accuracy of PWV from GEONET was statistically tested, and GEONET vividly monitored various atmospheric phenomena. All these analyses, however, attested critical necessity of knowing a few km-scale water vapor variations to improve the accuracy of GPS positioning and PWV retrieval. This led us to conduct a dense GPS network campaign with 75 receivers in a 400 km2area. A tomography analysis of slant path delays of GPS signals revealed a 3-D distribution of water vapors. Improvement of geodetic accuracy of GEONET was also tried using NWP data. GPS radio occultation (RO) method applied to GPS data observed by space-borne GPS receivers yielded a global-scale temperature distribution, which shed light on a vertical propagation process of atmospheric gravity waves in the tropics. GPS RO technique was also applied to mountain-based GPS downward-looking observation and succeeded in obtaining fine vertical temperature structure in the lower troposphere. In this paper, we summarize results of the “GPS/MET Japan” project, review subsequent relevant researches, and look at the future. We hope that this paper will encourage new studies aiming for further progresses not only on numerical weather prediction but also on the interdisciplinary sciences for understanding the global changes.
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[SPECIAL ISSUE FOR GPS/ACOUSTIC SEALOOR GEODETIC OBSERVATION (continued)]
ORIGINAL PAPERS
  • Tsuyoshi Watanabe, Keiichi Tadokoro, Shingo Sugimoto, Takashi Okuda, R ...
    2009 Volume 55 Issue 1 Pages 39-51
    Published: 2009
    Released on J-STAGE: January 31, 2012
    JOURNAL FREE ACCESS
    We have conducted observations of the seafloor crustal deformations around the Nankai Trough using a GPS/Acoustic technique. In the Kumano Basin, there are two seafloor benchmarks that are located about 60 and 80 km away from the deformation front of the Nankai Trough, respectively. The observations from 2005 to 2008 have illustrated that these benchmarks are moving at rates of about 5-6 cm/yr with uncertainties of 1-3 cm/yr relative to the stable Amurian plate. In this study, in order to estimate interplate coupling along the Nankai Trough, we calculated surface deformations accompanied with plate subduction in an elastic half-space and compared them with on- and offshore GPS velocities obtained by GPS/Acoustic technique. Then, we investigated the effect of observation for the seafloor crustal deformations on slip resolution on the plate interface. We conclude that offshore crustal deformation data provide good constraints for the estimation of fault slips at the shallower part of the plate interface, especially at the depths of 10-20 km, where slip resolution is low without using offshore geodetic data. Future additional crustal deformation observations on the seafloor would lead to the better estimation of seafloor velocities, which help us reveal strain accumulation process in the seismogenic subduction zone during interseismic period.
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  • Shingo Sugimoto, Keiichi Tadokoro, Ryoya Ikuta, Tsuyoshi Watanabe, Tak ...
    2009 Volume 55 Issue 1 Pages 53-63
    Published: 2009
    Released on J-STAGE: January 31, 2012
    JOURNAL FREE ACCESS
    The current analysis method in this study simultaneously estimates positions of seafloor transponders and temporal variation of acoustic velocity based on horizontally stratified structure of acoustic velocity. However, according to the result of numerical experiment using this method, the positioning might be affected by bias error using travel-time dataset made under the temporal variation of acoustic velocity with dual-period. The most probable cause of the bias error was misestimation of acoustic velocity with its uneven location in space. Thus to avoid misestimation, a constraint is added on the estimate of the acoustic velocity to the current analysis method. With this constraint, the result in numerical experiment showed that the positioning by the improved method has high repeatability in three components. As the constraint, for instance, the continuous measurement of temperature and pressure in seawater can be applicable.
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  • Shingo Sugimoto, Yukihito Osada, Tadashi Ishikawa, Takaya Asakura, Kei ...
    2009 Volume 55 Issue 1 Pages 65-85
    Published: 2009
    Released on J-STAGE: January 31, 2012
    JOURNAL FREE ACCESS
    The precision of three kinematic GPS softwares, GIPSY/OASIS II, IT, and GrafNav, was evaluated for seafloor geodetic observation. Positions of a rover station moving on a precise slider were determined from several reference stations located at different baseline lengths of 10 m, 30 km, 60 km, 90 km, 110 km, and 150 km. Reference solution was obtained from the shortest baseline (10 m) using each software, and then other solutions from longer baselines were compared with the reference one. The result showed that the precision (root-mean-square) of the positioning by the three softwares was ∼2 cm horizontally and ∼5 cm vertically. Moreover, even with the larger baseline lengths, there was no apparent decrease in positioning precision. However, it was observed that the precision was affected more by the spatio-temporal variation of atmospheric environment rather than by the variation of baseline length.
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TECHNICAL REPORT
  • Toshihiro Higashi, Yoichi Fukuda, Yoshiaki Tamura, Tadahiro Sato, Shuz ...
    2009 Volume 55 Issue 1 Pages 87-93
    Published: 2009
    Released on J-STAGE: January 31, 2012
    JOURNAL FREE ACCESS
    Since July 2005, we have repeatedly carried out absolute gravity measurements at Kamioka mine, Gifu, in the deep tunnel about 1 km below the ground surface. A superconducting gravimeter was already installed in the same place. The secular changes of gravity have been investigated using the absolute and the superconducting gravimeters. We have detected gravity changes of several tens of µgals (1µgal = 10-8 ms-2). The gravity changes detected by the absolute gravimeter show good agreement with gravity residuals in the superconducting gravimeter data. The gravity changes strongly suggest seasonal ones due to hydrological effects, especially to the snow effect.
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TUTORIAL
  • Katsuya Uenishi
    2009 Volume 55 Issue 1 Pages 95-102
    Published: 2009
    Released on J-STAGE: January 31, 2012
    JOURNAL FREE ACCESS
    Full-dressed geodetic survey in Japan was carried out after late 19th century. A few monuments of the survey facilities in the fields are still remained. Some survey markers, observation tables, memorials were placed by former organizations, Ministry of Interior, Earthquake Investigation Committee, and Geodetic Committee of Japan. This paper shows historical review of old geodetic survey activities and their monuments in the fields. The author would expect these historical monuments to be conserved.
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