A Station-Specific Regional Approach to Improve Galileo Single-Frequency Ionospheric Corrections over Europe

The European Galileo constellation employs the NeQuick-G model to provide ionospheric corrections for single-frequency positioning. This study proposes an improved correction algorithm that incorporates local ionospheric characteristics obtained from Digisondes and collocated GNSS receivers across Europe. The developed algorithm supports long-term, short-term, and real-time applications, with this study focusing on evaluating its real-time performance using retrospective data collected at 10 European stations between 2014 and 2023. In the proposed approach, station-specific CCIR coefficients are updated every five minutes using automatically scaled foF2 and M(3000)F2 measurements from local Digisondes. Additionally, the NeQuick-G effective ionization parameter (Az) is optimized using Total Electron Content (TEC) observations recorded by local GNSS receivers on the preceding day. The results demonstrate that the proposed algorithm generally provides more accurate ionospheric corrections than the standard NeQuick-G model, particularly during periods of high solar activity, achieving reductions in root mean square error (RMSE) of up to 3 TECU. Under moderate-to-low solar activity and at higher latitudes, improvements are less pronounced, with both approaches exhibiting comparable performance.