Ionospheric equatorial plasma bubble detection method with single-frequency GNSS L1 observations

Abstract GNSS positioning degrades significantly in equatorial and low-latitude regions. The culprit is ionospheric irregularities, particularly equatorial plasma bubbles which cause rapid, unpredictable fluctuations in Total Electron Content (TEC) and result in positioning and timing errors that can reach meters in severity. The standard solution uses dual-frequency receivers to measure TEC directly and accurately, but this approach has practical limits: the equipment is expensive, installation requires robust infrastructure, and many developing regions lack either.Single-frequency GPS L1 receivers are ubiquitous by comparison. They are cheaper, easier to deploy, and already common in ground networks worldwide. The challenge is that L1 alone cannot directly separate ionospheric delay from hardware biases. This study develops a hybrid framework to reconstruct TEC and detect EPBs using only single-frequency observations. The approach works in three stages. First, it extracts TEC from code-minus-carrier (CMC) combinations, a well-established technique but one that accumulates hardware-induced biases. Median filtering removes these biases. Second, the method trains a Gaussian Process model on Global Ionospheric Map (GIM) data to recover a smooth, physically consistent estimate of absolute TEC. Third, this reconstructed baseline is combined with the L1-derived TEC anomalies to preserve both large-scale ionospheric trends and the small-scale, localized fluctuations that mark EPB activity. We tested the framework at four IGS stations spanning low-latitude regions during the May and October 2024 geomagnetic storms. The technique successfully captures both the large-scale dynamics of storm-time ionospheric behavior and the localized irregularities characteristic of individual EPBs, enabling accurate detection. The result is a cost-effective alternative for real-time ionospheric monitoring that works with receivers already in the field.