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Gravity at sea--A memoir of a marine geophysicist.

Tomoda Y - Proc. Jpn. Acad., Ser. B, Phys. Biol. Sci. (2010)

Bottom Line: Professor Chuji Tsuboi made a number of unsuccessful attempts at developing a gravity meter that can be operated on a normal surface ship by reducing the noise by minimizing the motion of the gravity meter through a mechanical design.I have chosen a new approach toward the measurements of gravity on a surface ship by simplifying the mechanical part using a string gravity meter that was installed directly on a vertical gyroscope in combination with the numerical and/or electronic reduction of noises.The results reveal the fine structures of gravity field in and around trenches that provide important clues as to a number of geodynamic issues including the nature of the trench-trench interaction and the interaction of trenches with seamounts.

View Article: PubMed Central - PubMed

Affiliation: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan. fujimoto@aob.gp.tohoku.ac.jp

ABSTRACT
A history of studies on the gravity measurements at sea in Japan is reviewed with an emphasis on the contribution of the author. The first successful measurements at sea were made in 1923 by Vening Meinesz in the Netherlands using the pendulum apparatus installed in a submarine. However, the gravity measurements using a submarine are not convenient because the access to a submarine is limited. Professor Chuji Tsuboi made a number of unsuccessful attempts at developing a gravity meter that can be operated on a normal surface ship by reducing the noise by minimizing the motion of the gravity meter through a mechanical design. I have chosen a new approach toward the measurements of gravity on a surface ship by simplifying the mechanical part using a string gravity meter that was installed directly on a vertical gyroscope in combination with the numerical and/or electronic reduction of noises. With this gravity meter TSSG (Tokyo Surface Ship Gravity Meter), we firstly succeeded in measuring gravity at sea onboard a surface ship in July 1961 and the measurements have been extended to the northwestern Pacific and beyond. The results reveal the fine structures of gravity field in and around trenches that provide important clues as to a number of geodynamic issues including the nature of the trench-trench interaction and the interaction of trenches with seamounts.

Show MeSH
Loading the bifilar gravity pendulum on “Ryofu-maru”. We set up the “bifilar gravity pendulum” in the hold of “Ryofu-maru” of the Meteorological Agency which was anchored in Harumi wharf.
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fig03: Loading the bifilar gravity pendulum on “Ryofu-maru”. We set up the “bifilar gravity pendulum” in the hold of “Ryofu-maru” of the Meteorological Agency which was anchored in Harumi wharf.

Mentions: After another unsuccessful test cruise in 1957 on board “Ryofu-maru” (1,200 tons) of the Meteorological Agency (Fig. 5), we developed the second model in 1958 and revised it next year. A major improvement was made in the gimbal suspension. It was so designed that an averaged value of horizontal accelerations was fed to the torque motors to keep the gimbal horizontal. By choosing an appropriate time constant for the integrating circuit, it might be possible to have the gimbal be astatic for horizontal accelerations in shorter period and active in period longer than 20 s or so. We tried to measure gravity across the north Pacific in 1960 on board the cargo ship “Meirinsan-maru” (7,700 tons) of the Mitsui Senpaku Co. Ltd. However, we could not get successful results again. In those days, we knew little about the sea and the ship, and expected that the motion would probably be small if the ship was large and that everything might go well. Now I wonder if those machines were able to work had we chosen a calm sea. The lesson learned from these failures is that we must design the system in such a way that it must work perfectly under irregular motions of a ship. The most serious problem was how to keep the gravity meter vertical in such a condition.


Gravity at sea--A memoir of a marine geophysicist.

Tomoda Y - Proc. Jpn. Acad., Ser. B, Phys. Biol. Sci. (2010)

Loading the bifilar gravity pendulum on “Ryofu-maru”. We set up the “bifilar gravity pendulum” in the hold of “Ryofu-maru” of the Meteorological Agency which was anchored in Harumi wharf.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3037522&req=5

fig03: Loading the bifilar gravity pendulum on “Ryofu-maru”. We set up the “bifilar gravity pendulum” in the hold of “Ryofu-maru” of the Meteorological Agency which was anchored in Harumi wharf.
Mentions: After another unsuccessful test cruise in 1957 on board “Ryofu-maru” (1,200 tons) of the Meteorological Agency (Fig. 5), we developed the second model in 1958 and revised it next year. A major improvement was made in the gimbal suspension. It was so designed that an averaged value of horizontal accelerations was fed to the torque motors to keep the gimbal horizontal. By choosing an appropriate time constant for the integrating circuit, it might be possible to have the gimbal be astatic for horizontal accelerations in shorter period and active in period longer than 20 s or so. We tried to measure gravity across the north Pacific in 1960 on board the cargo ship “Meirinsan-maru” (7,700 tons) of the Mitsui Senpaku Co. Ltd. However, we could not get successful results again. In those days, we knew little about the sea and the ship, and expected that the motion would probably be small if the ship was large and that everything might go well. Now I wonder if those machines were able to work had we chosen a calm sea. The lesson learned from these failures is that we must design the system in such a way that it must work perfectly under irregular motions of a ship. The most serious problem was how to keep the gravity meter vertical in such a condition.

Bottom Line: Professor Chuji Tsuboi made a number of unsuccessful attempts at developing a gravity meter that can be operated on a normal surface ship by reducing the noise by minimizing the motion of the gravity meter through a mechanical design.I have chosen a new approach toward the measurements of gravity on a surface ship by simplifying the mechanical part using a string gravity meter that was installed directly on a vertical gyroscope in combination with the numerical and/or electronic reduction of noises.The results reveal the fine structures of gravity field in and around trenches that provide important clues as to a number of geodynamic issues including the nature of the trench-trench interaction and the interaction of trenches with seamounts.

View Article: PubMed Central - PubMed

Affiliation: Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan. fujimoto@aob.gp.tohoku.ac.jp

ABSTRACT
A history of studies on the gravity measurements at sea in Japan is reviewed with an emphasis on the contribution of the author. The first successful measurements at sea were made in 1923 by Vening Meinesz in the Netherlands using the pendulum apparatus installed in a submarine. However, the gravity measurements using a submarine are not convenient because the access to a submarine is limited. Professor Chuji Tsuboi made a number of unsuccessful attempts at developing a gravity meter that can be operated on a normal surface ship by reducing the noise by minimizing the motion of the gravity meter through a mechanical design. I have chosen a new approach toward the measurements of gravity on a surface ship by simplifying the mechanical part using a string gravity meter that was installed directly on a vertical gyroscope in combination with the numerical and/or electronic reduction of noises. With this gravity meter TSSG (Tokyo Surface Ship Gravity Meter), we firstly succeeded in measuring gravity at sea onboard a surface ship in July 1961 and the measurements have been extended to the northwestern Pacific and beyond. The results reveal the fine structures of gravity field in and around trenches that provide important clues as to a number of geodynamic issues including the nature of the trench-trench interaction and the interaction of trenches with seamounts.

Show MeSH