A Review on Global Ionospheric Maps and Potential Refinements

The ionosphere is the uppermost layer of the atmosphere between about 60 and 800 km of altitude. Information on the distribution of free electrons in the Earth's ionosphere is needed for many applications, including the mitigation of ionospheric range delay errors and space weather monitoring. Most of the existing global ionospheric models use ground based GNSS measurements to model total electron contents (TEC). The paper gives a state-of-art review on the generation, validation, and combination of the IGS provided real-time and post-processing global ionospheric maps (GIMs). Additionally, potential refinements to further improve the quality of existing global ionospheric maps will be presented and discussed, which mainly includes 1) the extraction of high-precision slant TEC information using precise point positioning ambiguity resolution (PPP-AR) technique, 2) the inclusion of near-real-time and real-time observation data to shorten the model time latency, 3) the combined use of ground and space geodetic observations to further improve the model spatial resolution, 4) proper generation of model accuracy information, and 5) the use of Artificial Intelligent (AI) technique for model nowcast and forecast.