Development of an Analysis Centre Software for multi-GNSS Precise Orbit and Clock Estimation

Real-time GNSS precise positioning has many societally important applications, such as geohazard monitoring (earthquake, volcano, tsunami early warning), real-time ionospheric and tropospheric monitoring, autonomous navigation and surveying and mapping. At Geoscience Australia, we are currently developing an Analysis Centre Software (ACS) package for multi-GNSS, multi-frequency data processing. The software package when complete, will support both real-time and post-processing of multi-GNSS data in either network or precise point positioning (PPP) modes. When released, the package will be freely available under an open source license. At present, the software uses the dual-frequency ionosphere-free code and phase observations from GPS L1&L2, BeiDou B1&B2 and Galileo E1&E5a in an Extended Kalman Filter (EKF) to estimate precise orbits and clocks products. The next phase of development will focus on implementing full multi-frequency data analysis in an un-differenced, un-combined approach with ambiguity resolution. To validate our current ACS v1.0 software release, we have analysed one week multi-GNSS data from ~100 globally distributed stations, estimating satellite orbits and clocks for GPS, Galileo and BeiDou constellations. Our preliminary comparisons with other IGS Analysis Centres results show ACS estimated 3-D orbit RMS differences at the ~5cm level for GPS, ~10cm level for Galileo, while BeiDou orbit RMS differences range from ~10cm to ~1m depending on the satellite type, e.g., MEO, IGSO or GEO. Comparison of the estimated satellite clocks against IGS Analysis Centre's products typically shows, GPS clock RMS differences of ~3cm, while BeiDou and Galileo clocks are at ~6cm.