Impact of Ionospheric Disturbances during Solar Cycle 25 on SLAS The DGPS-Based Augmentation Service of QZSS

Yuri Kato, Kazushi Suzuki, Ryo Ariyama, Tomotaka Kaneda, Tempei Kondo, Higuchi Motoki, Michi Nishioka, Septi Perwitasari, Takuya Tsugawa

Peer Reviewed

Abstract:	This report presents a technical evaluation of the impact of intensified solar activity and ionospheric disturbances during the solar maximum of Solar Cycle 25 (2024–2025) on the Sub meter Level Augmentation Service (SLAS) of the Quasi Zenith Satellite System (QZSS). SLAS provides sub meter level positioning accuracy across Japan based on the DGPS technique, using pseudo-range corrections (PRC) generated at 13 reference stations. However, since around 2022, a noticeable decline in positioning accuracy has been observed in parallel with increasing solar activity. Because increases in sunspot numbers and the occurrence of M class or stronger solar flares coincide with the timing of the accuracy Decrease, ionospheric disturbances are considered the primary contributing factor. To evaluate SLAS performance during the Solar Cycle 25 maximum, positioning accuracy was assessed at 26 evaluation stations—two for each reference station—and among them, the EBINO station exhibited the most pronounced Decrease. Therefore, EBINO was selected for detailed analysis of the periods when Decrease occurred. The analysis revealed that positioning accuracy Decrease was concentrated during time periods associated with elevated daytime ionospheric activity (UTC 03–12) and during specific seasons (September–October and January–February). Furthermore, analysis using TEC differences demonstrated that variations in ionospheric conditions between the reference and evaluation stations appear as correction residuals, confirming that the DGPS based method exhibits inherent sensitivity to spatial ionospheric gradients.
Published in:	Proceedings of the ION 2026 Pacific PNT Meeting April 13 - 16, 2026 Hilton Waikiki Beach Honolulu, Hawaii
Pages:	901 - 915
Cite this article:	Kato, Yuri, Suzuki, Kazushi, Ariyama, Ryo, Kaneda, Tomotaka, Kondo, Tempei, Motoki, Higuchi, Nishioka, Michi, Perwitasari, Septi, Tsugawa, Takuya, "Impact of Ionospheric Disturbances during Solar Cycle 25 on SLAS The DGPS-Based Augmentation Service of QZSS," Proceedings of the ION 2026 Pacific PNT Meeting, Honolulu, Hawaii, April 2026, pp. 901-915. https://doi.org/10.33012/2026.20635
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