Precise monitoring and a conclusive interpretation of temporal gravity variations at a given station is based upon accurate knowledge about the properties of the used instruments. Only the combination of concurrent sets of superconducting and absolute gravity measurements allow both. Whereas absolute gravimeters provide the scale and reference level, superconducting gravimeters enable to determine gravity variations with high sensitivity and temporal resolution. A method is proposed here to derive the scale factor and zero drift function of the superconducting gravimeter as well as a reliable survey of the instrumental stability of absolute meters with high precision without the need of gravity reductions. In this way it is possible to separate between geophysical signals and instrumental effects in the time series. Results for the stations Bad Homburg, Wettzell in Germany are presented, demonstrating the potential of the technique.

The gravimetric time series achieved from the combination of superconducting and absolute gravimeters are characterized by highest precision and long-term stability. If the effects of Earth and ocean tides, atmosphere and polar motion are removed, the residual curve is dominated by hydrological mass variations. A major source of these variations is water storage changes in the vicinity of the sensor. However, global variations contribute to the signal significantly. For three stations of superconducting gravimeters, a comparison of the principal components obtained from the residual gravity curve on the one hand and continental water storage from the WaterGAP Global Hydrological Model (WGHM) on the other hand is carried out. The results demonstrate a coherence of seasonal variations but a difference in the contribution of the local zone at the individual stations, which point out the need for a careful and site-specific examination of local effects.

Precise monitoring and a conclusive interpretation of temporal gravity variations at a given station is based upon accurate knowledge about the properties of the used instruments. The combination of concurrent sets of superconducting and absolute gravity measurements allow both. Whereas the absolute gravimeters provide the scale and reference level, the superconducting gravimeters enable to investigate gravity variations and to exploit the sources of the changes. The method proposed here permits to derive the scale function and zero drift of the superconducting gravimeter as well as a reliable survey of the instrumental stability of different absolute meters with high precision without the need of gravity reductions. keywords: absolute gravity, calibration, superconducting gravimeter, site of regional comparison.