Local hydrology, the Global Geodynamics Project and CHAMP/GRACE perspective: some case studies

We first quantify the influence of aquifers on gravity variations by considering local, regional and continental scales. We show that locally only the direct attraction of the underlying aquifer has to be taken into account. At continental (or global scales), the underground water masses act by direct attraction (due to the earth curvature), loading flexure and potential redistribution. We show that at the intermediate regional scale (saying a few kilometres to a few hundreds of kilometres), groundwater contributions can be neglected in practice. Afterwards, we illustrate the difficulties in tackling the local hydrological context by studying comparatively the geological and hydrogeological surroundings of three European Global Geodynamics Project (GGP) superconducting gravimeter stations (Strasbourg, Moxa, and Vienna). Finally, it appears clearly that hydrological variability and cycle characterisations constitute the up-to-date challenge while studying gravity variations in a large spectral range. That is why, gravity is used to quantify hydrological transfers, and overall when seeking for small signals from the Earth's deep interior or other environmental signals (atmosphere, oceans) where groundwater influence can be seen as a disturbance.