Precision gravimetry in the new Zugspitze gravity meter calibration system

Abstract

The precise calibration of relative gravity meters is essential for the accuracy of gravimetric surveys. We show that in the new Zugspitze calibration system established in 2004 – 2005 excellent accuracies of the linear calibration factor of relative gravity meters in the range of 1–2 * $10^{-5}$ can be obtained. The calibration system is particularly useful for the precise calibration of Scintrex linear quartz gravity meters. The key advantages of the new calibration system are (a) the large gravity range of up to 528 mGal and (b) the short transport time of instruments by cable cars between the absolute gravity reference stations. This allows improving the accuracy of the Scintrex relative gravimetric observations by carrying out numerous ties over large gravity differences in a day or less. We study the accuracy and repeatability of Scintrex CG3 and CG5 calibration observations and the influence of seasonal effects due to environmental mass changes based on a time series of 57 calibration experiments over a period of 22 months. We show that variable attraction of snow can cause considerable effects up to 40 $\mu Gal$, in particular on stations in the summit zone. This is confirmed by forward modelling using a hydrological snow model with a 1km grid. We conclude that gravity meter calibration should be preferably carried out between July and December when the snow effect is small and repeatability of calibration experiments is within ±10 $\mu Gal$.