Quality assessment of experimental IGS multi-GNSS combined orbits

Abstract

The International GNSS Service (IGS) Analysis Center Coordinator initiated in 2019 an experimental multi-GNSS orbit combination service by adapting the current combination software that has been used for many years for IGS GPS and GLONASS combinations. The multi-GNSS orbits are based on individual products generated by IGS and multi-GNSS Pilot Project analysis centers. However, the combinations are not yet considered to be the final products at this time. The goal of this research is to provide a quality assessment of the very first IGS experimental multi-GNSS combined orbits based on Satellite Laser Ranging (SLR) observations and the mean position errors from the orbit combinations. The errors available in the combined orbit files provide information about the consistency between orbits from different analysis centers, whereas SLR provides independent orbit validation results even for those satellites which are considered only by one analysis center, and thus, the quality of the combination is not provided in the orbit files. We found that the BeiDou-3 satellites manufactured by China Academy of Space Technology and Shanghai Engineering Center for Microsatellites are characterized by opposite SLR residual dependencies with respect to the position of the sun which means that the orbit models for BeiDou-3 need further improvement. Smallest SLR residuals are obtained for Galileo, GLONASS-K1, and GLONASS-M+ . However, the latter is characterized by a bias of + 29 mm. The mean standard deviations of SLR residuals are 23, 29, 87, 51, 40, and 72 mm for Galileo, GLONASS, BeiDou GEO, BeiDou IGSO, BeiDou MEO, and QZSS, respectively. The mean orbit combination errors in the radial direction are three times lower than those from SLR residuals in the case of MEO satellites and vary between 8 and 14 mm, whereas the orbit errors are four times lower than SLR residuals in the case of GEO and IGSO and equal to 11–21 mm.