Direct and local comparison between different ssatellite mission for the gravity field on-the-fly

Many different satellite missions are in project at the moment to estimate the global gravity field of the earth and its time variations. The principles of measurement are basically three, namely: the measurement of accurate orbit anomalies and of non gravitational forces acting on the satellite; the measurement of differential orbit anomalies and of their time variations along the line of sight of twin satellites; the measurement of the gradiometric tensor. In all three cases it is interesting to discuss the possibility of being able to compare the observations performed during a mission at different times and at points close in space, as well as to compare different kinds of observations from different missions approximately in the same area. This could produce on-the-fly calibration procedures and cross-calibration procedures. To reach this goal one can try to “localize” the observations so that the problem is reduced to the comparison of different functionals of the anomalous potential T in the same zone of space