Empirical Study of the Ionospheric Scintillation Effects on GPS Positioning Accuracy Over South East Nigeria

Ionospheric scintillation, driven by equatorial plasma bubbles and irregularities in the F-region electron density, degrades GPS signal quality and positioning accuracy over Nigeria's equatorial region. South East Nigeria, located within the equatorial ionisation anomaly trough, experiences particularly intense scintillation during post-sunset hours that affects survey-grade GNSS operations, mobile mapping, and precision agriculture applications. This study empirically characterises ionospheric scintillation effects on dual-frequency GPS positioning accuracy at the University of Nigeria, Nsukka, and Enugu State University of Science and Technology reference stations. The S4 intensity and phase scintillation index are computed from 1-Hz GPS signal data collected over 24 months. Positioning errors in both absolute single-point positioning and differential GPS modes are computed at 1-minute epochs and correlated with concurrent S4 indices. Results indicate that single-point positioning errors increase from 3.2 m under quiet conditions to 18.7 m during severe scintillation with S4 exceeding 0.8. Differential GPS positioning errors remain below 0.5 m for baseline lengths under 10 km even during moderate scintillation. A threshold-based scintillation alert model achieving 88 percent sensitivity is developed for GPS user advisory applications. Keywords: ionospheric scintillation, GPS accuracy, equatorial anomaly, South East Nigeria, S4 index