Hydrological influences in long gravimetric data series

Hydrological influences on the local gravity field may reach amplitudes in the order of 100 nm s−2 and extend over several months. This concerns precipitation as well as changes of the groundwater level. To take full advantage of the high capabilities of the modern superconducting gravimeters (high sensitivity, low and stable drift rate), hydrological data have to be incorporated in the gravimetric data processing, especially if long-term phenomena with small amplitudes are studied. Seven stations were selected (Boulder, Brussels, Moxa, Strasbourg, Sutherland, Wettzell, Concepción), meantime all included in the GGP co-operation, which made available not only their gravity data but also the appropriate auxiliary data (groundwater, precipitation). Besides the shape of the residual gravity curves also the δ-factors derived for the gravity effect of polar motion (annual wobble, Chandler wobble) may change significantly if corrections for the hydrological influences are applied. The extent of the hydrological influences is very different from station to station.