2025 Volume 71 Pages 34-42
Results of the experiment on retrieving spatial difference in gravity acceleration by using an iGrav superconducting gravimeter as a portable relative gravimeter are presented. In 2024, we had an opportunity of moving the iGrav （serial number 003） twice, namely from the Zao station （in Miyagi prefecture） to the Fuji station （in Yamanashi prefecture）, and then to the Asama station （in Nagano prefecture）. Absolute gravity values are known for all the three stations. The differences in absolute gravity acceleration are （236.21±0.03） mGal between Zao and Fuji and （37.95±0.10） mGal between Fuji and Asama （1 Gal＝0.01 ms－2）. In moving the iGrav between the stations, we kept the superconducting currents generating the supporting magnetic field untouched, so that the superconducting sphere was levitated during the transport. The gravity control of the iGrav was temporarily set to Strong Feedback both before the shutdown of the system at the old station and on the startup at the new station. We calibrated instrumental sensitivity of the iGrav using the data of absolute gravity measurements made at the Fuji station. The scale factor was found to be （138.57±0.27） mGal V－1 for Strong Feedback. Our estimates of gravity difference obtained with iGrav were （237.65±0.46） mGal between Zao and Fuji and （37.05±0.07） mGal between Fuji and Asama. These results have errors of about 1 mGal in the absolute sense and about 1–2％ in the relative sense.
