著者

風間 卓仁

出版者

北海道大学大学院理学研究院

雑誌

北海道大学地球物理学研究報告 (ISSN:04393503)

巻号頁・発行日

vol.83, pp.9-23, 2020-03-19

---

Relative gravity data is continuously collected using different types of portable relative gravimeters on a trial basis, toward the future utilization of continuous relative gravity measurements for monitoring spatiotemporal mass variations associated with volcanic activities. The gravity data is first recorded using the Tera Term software installed to a Windows-based PC; although a typical LaCoste & Romberg gravimeter does not have any devices to transmit its gravity value digitally, its analog voltage output from its readout socket can be converted to serial data format using an appropriate analog-digital converter. The recorded gravity data is then sent to an Ubuntu-based computer periodically to draw graphs of gravity time series. The graphs are finally uploaded to a web server so as to monitor temporal gravity variations anytime and anywhere. The above system for continuous relative gravity measurement was applied to the LaCoste G680 gravimeter, which was installed at the Kyoto-A gravity point, Kyoto University in September 2017. The G680’s gravity data in 2018 clearly showed time variations in short-period tide and annual instrumental drift. In particular, the instrumental drift was expressed by the linear gravity decrease of about 10 mGal/year and the additional annual gravity variation of about 1.5 mGal amplitude. These results suggest that typical LaCoste gravimeters can be utilized for continuous relative gravity measurements without major instrumental remodeling.