Numerical Velocity determination and Calibration Methods for CHAMP Using the Energy Balance Approach

More than two years of data of the champ satellite mission is available and the usage of the energy balance approach for global gravity field recovery has been successfully implemented by several groups around the world. This paper addresses two important aspects of the data processing. First, high-quality gravity recovery requires numerical differentiation of kinematic positions. Two methods are investigated using simulated and real dynamic data. It is shown that a third order Taylor differentiator is sufficient to reach good results. Second drift due to the accelerometer bias has to be corrected. Two possible approaches are discussed: cross-over calibration on the one hand calibration w.r.t. a reference model on the other hand. Currently the crossover calibration fails due to the insufficient accuracy of the crossover determination whereas the calibration w.r.t. a reference model gives good results.