Assessment of precise orbit and clock products for Galileo, BeiDou, and QZSS from IGS Multi-GNSS Experiment (MGEX)

The focus is on the quality assessment of precise orbit and clock products for the emerging Galileo, BeiDou, and QZSS systems. Products provided by Multi-GNSS Experiment (MGEX) over 2 years are used for evaluation. First, the products are assessed by orbit and clock comparisons among individual analysis centers (ACs), which give us an objective impression of their consistency. In addition, the precise orbits are verified by satellite laser ranging (SLR) residuals, which can be regarded as indicators of orbit accuracy. Moreover, precise point positioning (PPP) tests are conducted to further verify the quality of MGEX precise orbits and clocks. Orbit comparisons show agreements of about 0.1-0.25 m for Galileo, 0.1-0.2 m for BeiDou MEOs, 0.2-0.3 m for BeiDou IGSOs, and 0.2-0.4 m for QZSS. The BeiDou GEO orbits, however, have the worst agreements having a few meters differences. Clock comparisons of individual ACs have a consistency of 0.2-0.4 ns for Galileo, 0.2-0.3 ns for BeiDou IGSOs, 0.15-0.2 ns for BeiDou MEOs, 0.5-0.8 ns for BeiDou GEOs, and 0.4-0.8 ns for QZSS in general. The SLR validations demonstrate an accuracy of about 0.1 m for the current Galileo, BeiDou IGSO/MEO orbits, and about 0.2 m for QZSS orbits. However, the SLR residuals of BeiDou GEO orbits show a systematic bias of about -0.5 m together with a standard deviation of 0.3 m. Solutions of PPP with different products mostly agree well with each other, which further confirms the good consistency of orbits and clocks among ACs. After convergence, an accuracy of 1 mm to 1 cm for static PPP and a few centimeters for kinematic PPP is achieved using multi-GNSS observations and MGEX orbit and clock products. However, it should be noted that a few exceptions may exist throughout the evaluations due to the insufficient models, different processing strategies, and ongoing updates applied by individual ACs.