The Contribution of GGP Superconducting Gravimeters to GGOS

The network of more than 24 superconducting gravimeters (SGs) of the Global Geodynamics Project (GGP) is available as a set of reference stations for studies related to time-varying gravimetry. The inherent stability of the SG allows it to detect signals from a sampling time of 1 s up to periods of several years with a time-domain accuracy of 0.1μGal or better. SGs within the GGP network comprise a valuable set of stations for geodetic and geophysical studies that involve Earth’s surface gravity field. Experience has shown that SGs can be calibrated to an accuracy of 0.01–0.1 %, and that most instruments have a low, but well-modeled, drift of a few μGal/yr. For most purposes except the determination of an absolute gravity reference level, the SG is the best observation-style instrument we have today. SG data is now freely available, much of it going back to the early 1990’s, from the GGP database at ICET (International Centre of Earth Tides, in Brussels, Belgium) and GFZ (Potsdam, Germany). Frequently it is combined with other datasets such as atmospheric pressure and hydrology for studies of ground deformation and tectonics. One of the most interesting new ideas within GGOS (Global Geodetic Observing System) is the determination of the geocenter using a combination of satellite and ground-based gravimetry. The GGP network can provide a unique contribution through continuous data at the stations where absolute gravimeters (AGs) will be deployed. The combination David Crossley Department of Earth and Atmospheric Sciences, Saint Louis University, 3642 Lindell Blvd. St. Louis, MO 63108, USA, e-mail: [email protected] Jacques Hinderer EOST/Institute de Physique du Globe, 5 Rene Descartes, 67084 Strasbourg Cedex France of the two instruments is necessary to ensure that AG measurements are referencing the mean station gravity and not short-term gravity perturbations due for example to hydrology or meteorology. Another promising application is the use of SG sub-networks in Europe and Asia to validate time-varying satellite gravity observations (GRACE, GOCE).