Computation of Gravity Gradients for Europe for Calibration/Validation of GOCE Data

Abstract. The upcoming GOCE satellite mission is expected to map the Earth´s gravity field with unprecedented accuracy. Besides the instrument calibration on ground and in orbit, there is a need to check the calibration throughout the two measure-ment phases without direct interference with the satellite operation. One promising method for the validation and calibration of GOCE data is the use of ground gravity data in some well-surveyed areas, continued upward to satellite altitude. The concept of the least squares spectral combination technique is applied to the computa-tion of gravity gradients in space. The necessary methodology is developed, and an error analysis is performed considering the errors of the terrestrial gravity data and of the global geopotential model. The results show that accuracies at the level of a few mE (1 mE = 10-3 E, 1 E = 10-9 s-2) are possible. The practical computations are based on the gravity and terrain data collected within the frame of the European Geoid Project. The contribution of each of the data sets involved in the combination process (gravity, terrain, global model) is discussed. Further numerical studies are presented regarding the effect of the satellite altitude, the resolution of the input data, the integration radius, the employed global gravity model, and the use of terrain data. The results suggest to use a high-degree global model, terrain information to avoid alias effects, a data resolution of 5 ´ to 10´, and a sufficiently large integration radius (> 5°) for accuracies of a few mE