Calibration of Instrumental Offsets of Absolute Gravimeters FG5 #109 and #241 by Intercomparison at Tokyo and Mount Fuji

Abstract

In order to precisely calibrate the instrumental drift of superconducting gravimeters with absolute gravity measurements, instrumental offsets of the absolute gravimeters used for the measurements must be known to the precision on the order of 0.1 μGal. In this study, absolute gravimeters FG5 #109 and #241 owned by Earthquake Research Institute, The University of Tokyo were compared for precisely calibrating relative offsets of the instruments. Two experiments at Tokyo and Mount Fuji gave consistent results, though the uncertainties in the experiment at Tokyo were large. The experiment at Mount Fuji achieved calibration precision of 0.33 μGal. Frequencies of the Rubidium clocks used with the absolute gravimeters were also measured against the Hydrogen maser clock at Mizusawa VLBI Observatory, National Astronomical Observatory of Japan.