1 Validation of GRACE Data Using GGP stations from Europe and Asia David Crossley (1) , Caroline de Linage (2) , Jean-Paul Boy (2) , and Jacques Hinderer (2) , and Junyong Chang (1) (1) Department of Earth and Atmospheric Sciences, St. Louis University, 3507 Laclede Ave., St. Louis, MO, USA 63103 (crossleydj@gmail.com), (2) Ecole et Observatoire des Sciences de la Terre / IPG Strasbourg, 5 Rue Descartes, Strasbourg 67084 Cedex, France (Jacques.Hinderer@eost.u-strasbg.fr). Abstract We consider the validation of GRACE satellite data by ground gravimetry from the Global Geodynamics Project (GGP). Results are presented for central Europe, where 7 superconducting gravimeter stations have been operating through the period of GRACE (mid 2002 to present); our comparison extends previous results to the end of 2006. While the overall agreement between GGP and GRACE is consistent with the seasonal hydrology predicted by GLDAS model, many features in the gravity data differ in amplitude and phase. Using EOF decomposition, the amplitude of GLDAS is generally higher than GRACE, and much higher than the ground GGP signal. This is partly due to processing, but a major factor for the GGP data is the location of stations under the soil moisture horizon. This complicates the comparison with GRACE data. We also for the first time consider the small network of GGP stations in the Japan- Korea-China-Taiwan area, and find that the GRACE seasonal effect is complex. Good correlation between GLDAS and GGP exists for some stations, in particular Wuhan and Matsushiro, but again the phase inversion is apparent. It is clear that problems introduced by the coastlines in this part of the world will make validation even more difficult than in Europe. Keywords: Superconducting gravimeter, GRACE, hydrology, GGP, GLDAS Introduction To readers of BIM, the topic of ground validation of GRACE data is no doubt familiar. Some recent papers include Crossley (2004), Crossley et al. (2004), Crossley et al. (2005), Andersen et al. (2005), Andersen and Hinderer (2005), Hinderer et al. (2006), and Crossley et al. (2007a, 2007b). GRACE satellite gravity data has been used extensively for estimating the variability of continental hydrology, especially in locations of high rainfall, but also in areas such as the US Midwest where ground hydrology is well observed (Swenson et al., 2006). The data has also been compared to the ground deformation produced by the Sumatra-Andaman earthquake of 2004 (e.g. Lambotte et al., 2006; Han et al., 2006; Panet et al., 2007). In both instances, evidence has shown that the satellite gravity field is consistent with the predicted models, based on global land assimilation models and observed ground soil moisture in the first case, and on seismic observations in the other. Yet in neither case has the same type of data been compared, i.e. surface gravity data derived from GRACE with gravity observations on the ground. Given the size of the anticipated signal (typically a few microgal), the only instrument that is reliable at the microgal level is the superconducting gravimeter (SG), which is the main