Hans-Georg Scherneck, Marcin Rajner

Preparing for joint analysis of absolute gravity (AG) campaigns, this report investigates whether a stationary superconducting gravimeter (SCG) can provide a long-term stable measurement of site-dependent perturbations that help in reduction to the local value of little-$g$ and its secular rate of change. The crucial element concerns the discrimination of instrumental drift components from trends of physical origin, where biasses in the inferred long-term drift rate may offset the rate that the reduced AG campaigns deliver. Thus, the main objective is to include a set of gravity models and proxy series as complete as possible in the SCG analysis. Findings indicate consistency for $\dot{g}$ in the drift model at the 0.5~nm/s$^2$/yr level using observations at Onsala Space Observatory from 2009 to 2017. In pursuit of the overriding objective to improve the accuracy of secular rates of gravity owed to Glacial Isostatic Adjustment, our approach may even put numbers on a range of long-term changes due to atmosphere, hydrology, and non-tidal ocean loading, namely the rate biasses reported here.