AIUB-GRACE gravity field solutions for G3P: processing strategies and instrument parametrization

Abstract. This paper discusses strategies to improve the GRACE monthly solutions computed at the Astronomical Institute of the University of Bern (AIUB) which are contributing to the Horizon 2020 project G3P - Global Gravity-based Groundwater Product. To improve the AIUB-GRACE gravity field solutions, we updated the use of the Level-1B observations and adapted the background models, and improved the processing strategies in terms of instrument screening and parametrization. We used the latest Release 3 K-Band product (KBR) and star camera data (L1B RL03), and adopted the latest Release 6 of the Atmospheric and Ocean De-aliasing (AOD1B RL06) product. For the accelerometer parametrization, we used arc-wise full scale factor matrix and arc-wise third-order polynomial biases. The new accelerometer parametrization is effective to reduce noise over the oceans in gravity field solutions especially for the late years of the GRACE mission when the thermal control was switched off. In this paper, we show that the outliers in KBR antenna offset correction (AOC) are projected into the range-rate residuals; therefore, we used the KBR AOC as the main source for outlier detection and eliminated the AOC above a threshold for all data before the gravity field processing.