Long-Term Stability of Tilt-Controlled gPhoneX Gravimeters

Spring relative gravimeters are considered too unstable to provide useful information on long-term gravity variations. In this paper, we prove that the new generation of spring gravimeter gPhoneX can reach long-term stability at the mu Gal level (10 nm s(-2)) when the verticality of the gravimeter is maintained, if the instrumental drift can be correctly estimated. We conducted two comparisons with different gPhoneXs in different observatories and environmental conditions. In the Walferdange Underground Laboratory for Geodynamics in Luxembourg, we compared time series from the gPhoneX (with and without tilt control), with data from a superconducting gravimeter. We found an agreement at the mu Gal level when the tilt control is switched on. We validated this result by repeating the experiment at the Geodesy in Karstic Environment observatory in the south of France. The fit between the superconducting gravimeter and the gPhoneX hourly values gives similar results at all frequencies over 276 days of measurements. The linear correlation coefficient between the gPhoneX and superconducting gravimeter reaches 0.99, with a misfit of 6.0 nm s(-2). We demonstrated that tilt-controlled gPhoneXs are suitable for long-term gravity monitoring.