On GPS data quality of GRACE-FO and GRACE satellites: effects of phase center variation and satellite attitude on precise orbit determination

As the gravity formation flying spacecraft jointly developed by National Aeronautics and Space Administration and German Research Centre for Geosciences, the Gravity Recovery and Climate Experiment (GRACE) and GRACE follow-on (GRACE-FO) satellites have adopted the same K-band ranging system and orbit design in order to detect the Earth's gravity field information. Different from the BlackJack receiver onboard GRACE, a TriG GNSS receiver is loaded on the GRACE-FO satellites. The orbit determination accuracy of GRACE is better than 2.5 cm, but for GRACE-FO there is no comprehensive assessment of orbit accuracy. We discuss the quality of Global Positioning System data, as well as effects of phase center variation (PCV) model and attitude for GRACE and GRACE-FO. The results show that there is no significant difference in terms of rate of change in ionospheric delay (IOD) and multipath effect, which suggests that the performance of TriG receiver is as excellent as that of BlackJack receiver. After using PCV corrections, the root mean square (RMS) errors of kinematic and reduced-dynamic (RD) orbit residuals decrease by 0.4-0.5 and 0.6-0.9 mm, respectively. Satellite laser ranging RMS errors for RD orbit solutions are lower than 2.59 cm whether PCV corrections are used or not. The effect of attitude data on kinematic and RD orbits indicates that nominal attitude data can reliably replace measured attitude data in GRACE-FO orbit determination.