Improved Antenna Phase Center Offsets for BDS-2 IGSO/MEO Satellites Based on MGEX Long-Term Observations

For the purpose of further improving the solution accuracies of the orbital and geodetic parameters for BDS (BeiDou Navigation Satellite System) precise applications, this paper focuses on the enhancements of antenna phase center offsets (PCOs) for BDS-2 IGSOs (Inclined Geosynchronous Satellite Orbits) and MEOs (Medium Earth Orbits) through processing observations from a global tracking network. The daily estimated horizontal and vertical PCO time series of nearly three years from DOY (Day of Year) 001 in 2018 to DOY 180 in 2020 are obtained using the PANDA (Position And Navigation Data Analysis) software. The long-term PCO time series have seasonal variations and systematic effects along with the elevation angle of the Sun with respect to the orbital plane. Then, type-specific x-offsets and y-offsets of IGSOs and MEOs are comprehensively available considering the good consistency for the same satellite type. And a set of satellite-specific vertical offsets are recommended to BDS-2 IGSOs and MEOs since the low coherence of these satellites with the same type. Validation experiments are carried out for comparison between the original MGEX (Multi-GNSS Experiment) PCOs and the newly improved values (iMGEX PCOs for short), including the Precise Orbit Determination (POD) and Precise Point Positioning (PPP). Based on the orbital overlap analysis, the qualities of BDS-2 orbits show great enhancements in the along-track, cross-track and radial components, when the iMGEX PCOs are employed. Results of the independent assessment using SLR (Satellite Laser Ranging) also indicate the improvements on the radial component for C08, C10 and C11 satellites, and most of the orbit RMSs (Root Mean Squares) of iMGEX results decreased by 40.5% on average compared with the MGEX values. Additionally, the experimental station coordinates by static PPP achieve improvements at the rate of 27.1%, 32.6% and 28.4% in the east, north, and up component, respectively, in which more than a half stations realize sub-centimeter positioning accuracy in the north component using the iMGEX PCOs.