Evaluation of GNSS ionosphere prediction models Klobuchar-GPS, NTCM-G, and BDGIM: methodology and results for 2021–2024

Abstract As part of their satellite navigation messages, GPS, Galileo, and BDS broadcast coefficients of ionosphere prediction models. These models are intended to be used for the improvement of single-frequency code-based positioning. We compared vertical electron content derived from these models with those of the more accurate post-processing ionosphere model produced by the International GNSS Service (IGS). On a global scale and for the time period 2021–2024, the Klobuchar-GPS model corrects on average about 59% of the vertical ionospheric delays, the NTCM-G model and a slightly modified BDGIM model give a correction rate of about 74%, while the combination of the latter two models gives a correction rate of 77%. In the case of strong geomagnetic storms with large effects on the ionospheric total electron content, the performance of the prediction models degrades and the global daily correction rates may even drop to below 50%. Single-frequency GNSS receivers with access to all GNSS are recommended to apply ionospheric corrections based on the ionosphere model coefficients and algorithms of Galileo/NTCM-G or BDS/modified BDGIM, or a combination of both. The Klobuchar-GPS model should serve as a backup in case that Galileo and BDS navigation messages are not available.