Calibration of superconducting gravimeters by combination with absolute quantum gravimeters

Classically, the scale factor of superconducting gravimeters (SGs) can be determined by two approaches. A first estimate can be obtained by comparison of its observations with a theoretical Earth tide and precise ocean tide loading models, after correcting for the effects of polar motion and atmosphere on gravity. However, an independent estimation from existing tide models is preferred and can be achieved through the combination with parallel absolute gravity observations, usually performed with classical free-fall gravimeters. In this case, absolute gravity observations are carried out only over a few days to limit the mechanical wear of these instruments, and preferably during periods of spring tides to enhance the signal-to-noise ratio.

In this study, we investigate the use of the quantum gravimeters AQG by Exail for the calibration of superconducting gravimeters at the Geodetic Observatory Wettzell, Germany. To do so, continuous absolute gravity measurements were carried out for different periods of time and up to three months and combined with the SG observations. Scale factors were estimated through a least-squares adjustment, considering different time windows. Although the AQGs have a much larger scatter of individual experiments than FG5 absolute gravimeters, their benefit is considerably longer and continuous observation epochs, that are proved to be important also by synthetic data. A good agreement of the calibration factors with previous estimations was found, demonstrating the potential of quantum gravimeters to calibrate SGs.