Time-variable gravity field determination from GRACE-FO data at AIUB

Time-variable gravity field determination from GRACE-FO data at AIUB We study gravity field determination from GRACE-FO satellite-to-satellite tracking using the inter-satellite K-band link and kinematic positions of the satellites as observations and pseudo-observations respectively. We employ 10-second kinematic positions from a precise point positioning where the undifferenced carrier phase ambiguities are fixed to integer values using observation-specific phase bias products from the CODE analysis centre. We present an up-to-date GRACE-FO time series computed with the Celestial Mechanics Approach extended by empirical noise models derived from the post-fit residuals to better characterise the stochastic behaviour of both observation types. We investigate the interplay between the empirical noise model and the co-estimation of stochastic parameters set-up to absorb unmodelled signal (short term mass variations, accelerometer errors etc.). We validate our results of GRACE-FO 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