Long-term Gravity Series in Combination with Space Techniques at Medicina, Italy

Combining observed vertical height and gravity changes at the same location is not an ordinary task because of possible mass redistribution effects caused by e.g. ground water, atmosphere and the ocean. At Medicina uninterrupted gravity records are available since the beginning of 1998. To determine the instrumental effects of the Superconducting Gravimeter (SG) repeated absolute gravity observations are performed at least once a year, but often more frequently, two or three times a year. Over the 1998-2003 observation period, the long-term gravity signal is a composition of seasonal effects with a superimposed, mostly linear, trend. For an appropriate modeling and interpretation of the gravity data record, additional observations from different techniques, namely CGPS (continuous GPS), InSAR and several meteoclimatic data series are being collected. Geodetic space techniques provide the means to monitor continuously in a unique global reference system three dimensional station coordinates on the Earth's surface thus allowing the computation of high-accuracy horizontal as well as vertical velocities. Whereas CGPS observations provide pointwise information, i.e. the local behavior of a station, the InSAR technique can contribute more to acquire information on the regional deformation effects. To enlarge the local view to a regional area is important because the gravimeter is affected by both local and regional signals. All the available information is used to model the environmental effects and verify the deformation and mass attraction components by the observed height and gravity variations.