Evaluation of ionospheric correction models in multi-GNSS single-frequency SPP

The accuracy of Global Navigation Satellite System (GNSS) positioning is primarily limited by the adverse effects of ionospheric delays. In single-frequency single point positioning (SF-SPP) solutions, these effects are typically mitigated through the utilization of ionospheric correction models. For this purpose, a variety of ionospheric models are developed and broadcast by GNSS satellites. They include Klobuchar, NeQuick-G/NTCM-G, and BDGIM for GPS, Galileo, and BDS-3 systems, respectively. Moreover, the International GNSS Service (IGS) Real-Time Service (RTS) project has enabled the development of Real-Time Global Ionosphere Maps (RT-GIMs), which can also support real-time positioning. Given the significant impact of ionospheric delay on satellite navigation positioning errors, it is crucial to analyze the accuracy of the available ionospheric models. Therefore, based on multi-GNSS observations obtained from 30 IGS stations, the performance of the ionospheric correction models in SF-SPP is assessed. In this study, precise geodetic products are employed to reduce the influence of geometry-related error sources on the positioning solution and, hence, to emphasize the impact of the ionosphere models. The analyses are performed for the two-month period in 2020 marking the beginning of the 25th solar cycle. The positioning results revealed large discrepancies in the performance of the ionospheric correction models over different modified dip (MODIP) latitude regions. Among the broadcast models, the best results are obtained for the NTCM-G model, achieving an average 64% improvement in positioning accuracy compared to the uncorrected solution. However, RT-GIM allowed for an even better improvement of 72%, confirming the favorable applicability of the IGS RTS products to SF-SPP.