Studies on global gravity changes by means of absolute gravity measurements at the GGP-JAPAN superconducting gravity stations.

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The goal of this study is to determine calibration factors of superconducting gravimeters of the GGP(Global Geodynamic project)-Japan stations, and to obtain precise gravity data sets, which can be used for the comparison with the satellite gravity data such as GRACE, by means of absolute gravity measurements.For this purpose, we conducted absolute gravity measurements by our own hand at the GGP-Japan sites of Bandung (Indonesia) in 2002, Syowa Station (Antarctica) in 2003 and Canberra (Australia) in 2004, in addition to the GGP-Japan domestic sites of Kyoto, Esashi and Matsushiro. Absolute gravity measurements at Ny-Alesund, the other GGP-Japan site in Arctic area, were also conducted in cooperation with European researchers. Moreover, we conducted additional absolute measurements in Yogyakarta and Tibinon (Indonesia), and in Perth (Australia) for future references of secular gravity changes.As the results of this study, besides the originally intended outcome, namely the determination of the calibration factors of the superconducting gravimeters at the GGP-Japan sites, we established several absolute gravity stations for detecting future gravity changes. Especially the absolute gravity measurement conducted by this research was the first one in the history of Indonesia, and it also played a big role to enhance the gravity reference network in Indonesia.On the other hand, from the viewpoint of the secular gravity changes, we detected the gravity change expected from the postglacial rebound in Syowa Station, and we also succeeded in detecting the gravity change associated with present day ice melting in Ny-Alesund.