Japan-China International Gravimetric Connection(III). Sensitivity Characteristics and Measurement Accuracy of LaCoste & Romberg Gravimeters(Model G).:—Sensitivity Characteristics and Measurement Accuracy of LaCoste & Romberg Gravimeters (Model G)—
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概要
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An international gravimetric connection between Japan and China as well as domestic ones in both countries were carried out during the period from October 1985 to February 1986 by means of four LaCoste & Romberg gravimeters (G-196, G-305, G-484 and G-605) for the purposes of (1) calibrating scale values of each gravimeter employed, (2) precisely determining a gravity value at each measured station occupied, (3) establishing a precise gravity net composed of 24 gravity stations in the standard baseline field of gravity values in Lushan Mountains recently arranged by the Chinese authority, (4) experimentally reconfirming specific characteristics of mechanical sensitivity of La Coste & Romberg gravimeters revealed on some gravimeters through the international gravimetric connections along the Circum-Pacific zone performed in 19791982, and (5) clarifying the dependency of gravimeters, from data obtained under various measurement conditions, on disturbing environmental effects. The present article deals with the purpose (4) among them. During the whole course of the present investigations, a direct calibration of all the gravimeters employed was carried out as frequently as possible together with a sensitivity calibration at the time of every gravity measurement. Results obtained through examinations on the static characteristics of the gravimeter are summarized as follows: (1) The dependency of an optimal offset angle for the optical method of gravity measurements on a gravity value at the measured station has fully been ascertained through the investigations. On the contrary to this fact, an optimal offset angle for the readout method of gravity measurements has been ascertained to have quite different characteristics; namely, it depends on a gravity value and has time-dependent character. This character was revealed to be caused by instability for the zero-offset control of a readout amplifier. Without taking frequent and careful adjustments for the zero-offset of the readout amplifier, measurement accuracy for the readout method of gravity measurements becomes significantly worse according to a setting error along the longlevel of the gravimeter. (2) The readout system equipped in the gravimeter is not guaranteed for both longterm and short-term stabilities. Unlike its instantaneous high resolution, this problem in the short-term instability guarantees measurement accuracies in dial readings with the readout method for gravity measurements of only about the same order or less compared to those with the optical method for gravity measurements. (3) The resolution of bubble-type levels for the gravimeter's setting is limited to about ±10 seconds of arc in ordinary measurement conditions and it may reach up to ±15 seconds of arc in extremely severe measurement conditions. Therefore, it strongly requires to adjust bubble positions close to the optimal ones for attaining a high measurement accuracy concerning the setting positions of the gravimeter. (4) The gravity measurements had been accomplished with an accuracy of a few pgals usually and 5 pgals at maximum concerning the setting accuracies of the gravimeter throughout the whole period of the investigations.
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日本測地学会 | 論文
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