Modernizing the SWEPOS Ionosphere Monitoring Service: Ensuring Reliable Network-RTK Performance During the Approaching Solar Maximum

Martin Håkansson, Kibrom Ebuy Abraha, Kent Ohlsson, Tomas Holmberg, Tong Ning, and Martin Sundlöf

Abstract:	This paper presents the modernization of the SWEPOS ionospheric monitoring service, originally built for the 2013–2014 solar maximum. SWEPOS, operated by Lantmateriet, provides nationwide Network-RTK in Sweden based on a network of ¨ approximately 480 permanent GNSS stations used for real-time positioning with centimeter-level accuracy. Ionospheric variability, which is affected by solar activity, local time, season, latitude, and traveling ionospheric disturbances (TIDs), degrades precise GNSS positioning because rapid spatiotemporal changes invalidate the linear interpolation assumptions used for ionosphere modeling in Network-RTK and PPP-RTK. With the next solar maximum expected in 2025, we redesigned the monitor to reflect evolving conditions, multi-GNSS availability, improved receivers, and an expanded network. The updated system quantifies spatial ionospheric variability by comparing an interpolated delay, derived from a surrounding triangle of stations, to the measured delay at a central “truth” station. This calculation is repeated every 30 s over a rolling one-hour window for 112 station-based triangles (previously 12). The monitor also estimates Total Electron Content (TEC) and the Rate of TEC Index (ROTI). New visualization and alerting, including interactive maps, time-series views, and user notifications, enable detailed spatiotemporal tracking and timely warnings during geomagnetic storms. We evaluate the monitor against I95, IRIM, and observed network-RTK performance, which includes positioning accuracy and carrier phase ambiguity resolution. Results show a strong correlation between the monitor’s variability metric and network-RTK reliability, supporting its use as an operational indicator of when interpolated corrections match true ionospheric delays. The modernization strengthens centimeter-level positioning for surveying, precision agriculture, construction, and machine guidance under elevated solar activity.
Published in:	Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025) September 8 - 12, 2025 Hilton Baltimore Inner Harbor Baltimore, Maryland
Pages:	814 - 822
Cite this article:	Håkansson, Martin, Abraha, Kibrom Ebuy, Ohlsson, Kent, Holmberg, Tomas, Ning, Tong, Sundlöf, Martin, "Modernizing the SWEPOS Ionosphere Monitoring Service: Ensuring Reliable Network-RTK Performance During the Approaching Solar Maximum," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 814-822. https://doi.org/10.33012/2025.20371
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