Verification of champ accelerometer observations

Abstract

CHAMP is the first satellite that provides high-accuracy accelerometer observations with the aim of separating non-conservative accelerations from gravity when analyzing the CPS satellite-to-satellite tracking (SST) observations. An accuracy assessment of the accelerometer observations is required in order to find the best strategy for incorporation of these observations in the gravity field estimation. A number of methods has been investigated to estimate accelerometer bias and scale factor values. First, the accelerometer observations were compared with non-conservative accelerations predicted by an atmospheric density model. Second, bias and scale factors were estimated in CHAMP precise orbit determination where the accelerometer observations were used to complement the gravity and other conservative force models. Third, these accelerometer parameters were estimated in a gravity field model adjustment experiment. The sensitivity of all three methods with respect to the a priori gravity field model was investigated. It was found that the most stable accelerometer parameter values were obtained with the first method when using a priori gravity field models in which already use was made of CHAMP CPS SST and accelerometer data. In case of relatively large a priori gravity field model errors, the third method indicates that simultaneous gravity field and accelerometer parameter estimation is required in order to obtain reasonable bias and scale factor values, supporting the results obtained with the first method. All methods indicate that for the radial, along-track and cross-track accelerometer components different bias values need to be applied, but that the scale factors seem to converge to one common value equal to about 0.8.