Impact of x-class solar flares on GPS l_1 and l_2 signal to noise ratio (snr) at Nagongera receiver, Uganda during the solar cycle 25 maximum.
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Date
2026
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Busitema University
Abstract
The 2025–2026 maximum of Solar Cycle 25 was characterised by frequent X-class solar flares capable of producing intense X-ray radiation that can disrupt GPS signal propagation through the ionosphere. Uganda's Busitema University GNSS (BUSG) receiver at Nagongera is located in the equatorial ionospheric region, where GPS signals are strongly influenced by the Equatorial Ionospheric Anomaly (EIA). However, the frequency-specific effects of X-class solar flares on GPS signal quality at this station have not previously been investigated. This study assessed the impact of four daytime X-class solar flare events (X5.1, X4.0, X1.6, and X4.2) that occurred between November 2025 and February 2026 on the Signal-to-Noise Ratio (SNR) of GPS L1 and L2 signals. SNR time series were extracted from observation files, and flare-induced degradation was quantified by comparing flare-period observations with a 30-minute pre-flare baseline. The results showed that the L2 signal consistently experienced greater degradation than L1 during all four flare events. The X5.1 flare produced the largest reduction in L2 SNR, with values falling below the commonly used carrier-tracking threshold, indicating a likely loss-of-lock condition. During the X4.2 event, the observed vulnerability ratio closely matched the prediction of the Appleton-Hartree theory, providing empirical support for its application under equatorial ionospheric conditions. These findings demonstrate that X-class solar flares can significantly degrade dual-frequency GPS signal quality at Nagongera and highlight the importance of incorporating space weather information into GNSS-based geodetic and positioning operations in Uganda.
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Undergraduate research report
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Besigye, B. (2026). Impact of x-class solar flares on GPS l_1 and l_2 signal to noise ratio (snr) at Nagongera receiver, Uganda during the solar cycle 25 maximum. [Unpublished undergraduate research report]. Busitema University.