The Combined Real-Time Global Ionospheric Map for Operational Ionospheric Space Weather Monitoring

Space-based radio systems in L-band, like the Global Navigation Satellite Systems (GNSSs), are severely affected by ionospheric errors, which are known to be up to tens of meters in magnitude. In the case ionospheric propagation errors are not properly corrected, performance of navigation and communication applications based on GNSS radio signals can be severely degraded. The availability of regional and global tracking networks of GNSS receivers provides the opportunity to monitor continuously the variability of ionospheric electron contents for more than 20 years, and more recently in real time. Using the global multi-frequency and multi-constellation GNSS measurements provided by the International GNSS Real-Time Service (IGS-RTS), the Chinese Academy of Science (CAS), Centre National d’Etudes Spatiales (CNES) and Universitat Politècnica de Catalunya (UPC) started to routinely generate real-time global ionospheric maps (RT-GIMs) since 2017 [1] , [2] . Such RT-GIMs have been widely used in real-time GNSS precise positioning and ionospheric space weather monitoring, but the performance of RT-GIMs from individual analysis centers (ACs) are largely affected by the stability of RT-GNSS data streams. To provide a more stable real-time ionospheric correction stream, UPC adapted its post-processing GIM combination method, which has been successfully applied in the combination of IGS rapid and final GIMs, and used to combine the experimental IGS RT-GIM [3] . Following UPC’s RT-GIM combination activity, CAS also started RT-GIM combination using real-time streams from CNES, UPC, Wuhan University (WHU), and CAS itself since late-2021 (see Table 1 ).