測地学会誌

VLBI測地技術の開発とプレート運動の実証

近藤哲朗

2004 年 50 巻 4 号 p. 245-262
発行日: 2004/12/25
公開日: 2011/03/01

DOIhttps://doi.org/10.11366/sokuchi1954.50.245

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A very long baseline interferometry (VLBI) technique was originally developed to study radio source size and structure with high angle resolution by utilizing atomic clocks and magnetic recording systems. In the late 1970's VLBI came to be used for precise geodetic measure ments by the development of technique called bandwidth synthesis to measure group delays with sub-nanosecond accuracy. In the United States, VLBI system named Mark-III was devel oped for precise geodetic measurements and started operation. In the same period, satellite laser ranging (SLR) demonstrated its high-accuracy capability for geodetic measurements. NASA started the Crustal Dynamics Project (CDP) in 1979 to study the dynamic motion of the surface of the earth by using these space techniques. Since the accuracy of VLBI and SLR at that time was about 3 cm, a series of measurements spanning several years was expected to reveal actual plate motions with the formal velocity uncertainty less than 1 cm/year. In Japan, the Radio Research Laboratory (RRL) (presently NICT: National Institute of Information and Communications Technology) initiated VLBI and has led the technology developments from the beginning. NICT started the developments of the first VLBI system (K-1) in 1974, and carried out the first VLBI experiment in Japan successfully in 1977. This success led to the developments of precise VLBI system (K-3) for geodetic use, which is designed to be compatible with the Mark-III system. In 1983, NICT succeeded in the first Japan-US VLBI experiment using the K-3 system. NICT then joined regular CDP experiments with the K-3 system from 1984 to directly measure the motion of the Pacific plate. The motion of the Pacific plate was detected as early as in the next year. NICT then started to develop a new VLBI system named K-4 in 1987, which realized easy operation and transportation. K-4 was operated at Minamitorishima (Marcus Island), which is the only island in the Japanese territory located on the Pacific plate, and contributed to the direct measurements of the motion of the Pacific plate in Japan. Thereafter NICT has led the developments of VLBI in the world, such as real-time VLBI systems, gigabit recording VLBI systems, internet VLBI(e-VLBI) systems, and the standardization of the interfaces and software protocols.

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遠方からの応力や,内圧を受ける場合の,無限弾性体中の円管の変形

坂田正治

2004 年 50 巻 4 号 p. 263-280
発行日: 2004/12/25
公開日: 2010/09/07

DOIhttps://doi.org/10.11366/sokuchi1954.50.263

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Crustal deformation is routinely observed with borehole tiltmeters and/or strainmeters. In most cases a borehole tiltmeter is fixed to the borehole casing by a clamping device. When the borehole is deformed by external stress, the center of the vessel shifts from the origi nallocation, and this shift may cause a spurious tilt. To estimate this possible false tilt, we need an analytical method to calculate the deformation of cased boreholes under such condi tions. A borehole strainmeter, regardless of type, is installed into an open borehole with mortar or cement grouting, and we measure the deformation of the cylindrical vessel under the outer stress field. The relation between deformation of a cylinder and the stresses acting at infinity is important in the derivation of strain. The author treated two-layer models, composed of an inner metal cylinder and outer elastic medium, in his first paper regarding the Sakata-type three-component strainmeter (1981), in which the effects of casings, as well as formulas to express stress and displacement distributions were discussed. In this paper the method for two-layer models is applied to three-layer models, in which the intermediate grouting strata are considered. Coefficients in the formulas to describe the stress and displacement distributions are obtained by solving the simultaneous equations in the text. In addition the deformation of a metal cylinder submitted to fluid pressure on the inner surface is treated. The results may be applicable to estimate the effects of atmospheric pressure changes in boreholes that contain water.

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絶対重力計開発の経緯と現状

―佐久間晃彦先生を偲んで―

坪川恒也

2004 年 50 巻 4 号 p. 281-294
発行日: 2004/12/25
公開日: 2010/09/07

DOIhttps://doi.org/10.11366/sokuchi1954.50.281

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　佐久間式絶対重力計で有名な佐久間晃彦先生が,2004年8月19日パリ郊外セーブル市の自宅で逝去されました.享年73歳.謹んでご冥福をお祈り致します.　先生は,昭和6年宮城県仙台市にお生まれになり,昭和28年(1953)東北大学理学部物理学科卒業と同時に,当時の通産省中央計量検定所(現在の産業技術総合研究所,計量研究所)に入所され,日本で最初に自由落下方式による絶対重力計の開発を手掛けられました.その後,昭和35年にフランスに渡り,国際度量衡局(BIPM)の研究員として,平成8年までの36年間に渡って,重力加速度の絶対測定の研究に従事され,特に,佐久間式と総称される,投げ上げ方式の絶対重力測定法の確立および製品化と,絶対重力網の整備に大きな功績を残されました.まさに絶対重力測定の研究に,半生を捧げられたと言っても過言ではありません.佐久間先生がBIPMに入所された頃は,国際機関とはいえ白人主導の組織の中で,日本人が単独で乗り込んで研究することに,かなりご苦労されたのではないか,と推察致します.そのような環境の中でも,絶対重力測定をテーマとした精密計測に対する佐久間先生の熱いお気持ちが,あのように独創的な絶対重力計として実を結び,まさに日本人の優秀さを世界に認あさせたのではないでしょうか.　佐久間先生には,緯度観測所の固定局型の佐久間式絶対重力測定装置の導入当時から,ご指導頂きました.穏やかな物腰ながら信念を持った,古き良き時代の典型的な日本人との印象を受けました.図1は1989年の第3回絶対重力計国際比較測定をBIPMで主催された時のスナップショットです.ここでは,佐久間先生という偉大な大先輩を偲んで,絶対重力計の開発に携わってきた一人として先生を偲びつつ,絶対重力計開発の経緯と現状について述べたいと思います.

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報告

渡部豪, 今西祐一

2004 年 50 巻 4 号 p. 295-303
発行日: 2004/12/25
公開日: 2010/09/07

DOIhttps://doi.org/10.11366/sokuchi1954.50.295

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