Time-variable gravity field determination from GRACE Follow-On data at the AIUB

At the Astronomical Institute of the University of Bern, we study gravity field determination from GRACE Follow-On satellite-to-satellite tracking using the inter-satellite link (KBR and LRI) and kinematic positions of the satellites as observations. The kinematic positions are obtained from a precise point positioning, where the carrier phase ambiguities are fixed to integer values. We use a simplifiedstochastic model based on epoch-wise covariance information, which may be efficiently derived in the kinematic point positioning process, and extend this model by an empirical noise model derived from the residuals of a reduced-dynamic orbit fit of the kinematic positions to correctly characterise their stochastic behaviour. In addition, we use empirical covariances of range-rate residuals to characterisethe inter-satellite link noise. We investigate the interplay between the empirical noise model and the stochastic parameters of our Celestial Mechanics Approach (CMA) for gravity field determination. We validate the performance of our gravity field determination by analysing the residuals of combined orbits calculated using both kinematic positions and K-band data, and by analysing the quality of co-estimated gravity field solutions.Furthermore, we provide an update about on-going investigation regarding GRACE Follow-On at theAIUB.