Analyzing high temporal-resolution of GNSS-based ionospheric VTEC over Nigeria

Abstract

This study focuses on high-temporal-resolution Vertical Total Electron Content (VTEC) estimation over Nigeria, which is crucial for enhancing satellite-based applications. Utilizing RINEX, IONEX, and SP3 data from 2011 across 10 stations, the research integrates a novel VTEC model (LIMS) based on orthogonal transformation, achieving an unprecedented 10-minute temporal resolution sampling. The model incorporates multi-Global Navigation Satellite Systems (GNSS) constellations. Geomagnetic and solar activity impact assessments involve the Ap index, sunspot number, and DSt index. Specifically, the DSt index for March 16–18, 2015, analyzes the geomagnetic storm of St Patrick’s Day. Validation compares LIMS with International GNSS Service (IGS), Center for Orbit Determination in Europe (CODE), and International Reference Ionosphere (IRI-2020) estimates, showing strong correlations during various conditions. Daily VTEC patterns reveal the lowest values in the early morning, a midday peak, occasional double peaks, secondary maximum, and post-sunset enhancements, especially during equinoxes. Seasonal analysis highlights the highest mean VTEC in September Equinox and December Solstice, and the lowest during June Solstice. Spectral analysis identifies prominent diurnal, semi-diurnal, and sub-diurnal frequency components. This research significantly advances the understanding of VTEC in Nigeria, offering a valuable tool for precise positioning, satellite communication, and space weather forecasting. Notably, 9 stations processed 2011 data, while one station from this group and an additional station were used for a 3-day storm analysis in 2015 due to data availability.

Keywords

• GNSS
• TEC
• Secondary maximum phenomena
• Spectral analysis
• Orthogonal transformation