The Combined Real-Time Global Ionospheric Maps for Precise GNSS Applications

Benefiting from the global multi-frequency and multi-constellation GNSS measurements provided by the International GNSS Real-Time Service (IGS-RTS), real-time global ionospheric maps (RT-GIMs) have been provided by several ionospheric analysis centers of the International GNSS Service (IGS) since 2017. Considering the potential unstable ionospheric streams from individual analysis centers in real applications, we propose a sliding window based differential slant total electron content (dSTEC) weighting technique for the combination of Real-Time Global Ionospheric Maps (RT-GIMs). The combined RT-GIMs are generated using real-time ionospheric streams from the Chinese Academy of Sciences (CAS), Centre National d’Etudes Spatiales (CNES), Polytechnic University of Catalonia (UPC) and Wuhan University (WHU). The performance of combined RT-GIMs is validated in both ionospheric correction and positioning domains. The evaluation in the ionospheric correction domain is performed by comparison with the IGS final combined GIM, i.e. the IGS-GIM, as well as the independent ionospheric TEC observables derived from the Jason-3 altimetry and near-real-time DORIS observation data. The positioning performance of combined RT-GIMs is also evaluated in ionospheric corrected single-frequency standard point positioning (SF-SPP) and ionospheric constricted single-frequency precise point positioning (SF-PPP), by analyzing the 95% quantile of positioning residuals. Compared to IGS-GIM corrected results, the positioning accuracy of our combined RT-GIMs decreases by 5.1% and 6.8% in SF-SPP and SF-PPP analysis, respectively. When compared to BDGIM (the BDS-3 global broadcast ionospheric model) corrected results, the positioning accuracy of combined RT-GIMs increases by 17.2% in SF-SPP and 9.8% in SF-PPP, respectively. CAS combined RT-GIM streams are transmitted in both RTCM-SSR (IONO01IGS0) and IGS-SSR (IONO01IGS1) standards, which are accessible from the IGS (products.igs-ip.net:2101) casters since January 2022.