Impact of ionospheric delay on GNSS in a low-latitude region: a case study of Ogbomoso, Nigeria

Accurate positioning and timing services are critically dependent on Global Navigation Satellite Systems (GNSS); however, their performance is often degraded by ionospheric delay. This study evaluates the impact of ionospheric delay on GNSS positioning accuracy over Ogbomoso, Nigeria (≈ 8.1° N, 4.2° E), using one year of GNSS observations data recorded at 4 Hz with a u-blox ZED-F9P receiver. The data were converted to RINEX format using the RTKLIB suite and subsequently processed with the GPS-GOPI software to compute the Total Electron Content (TEC) and related parameters required for estimating the ionospheric delay. The positioning accuracy was then assessed using the Single Point Positioning (SPP) technique, evaluated through key statistical performance metrics including the Two-Distance Root Mean Square (2DRMS), Circular Error Probable (CEP), Spherical Error Probable (SEP), and Mean Radial Spherical Error (MRSE) indices. The results revealed the TEC, ionospheric delay, and geomagnetic disturbances coupling effect on SPP. It also showed that ionospheric delay exhibited seasonal modulation, with higher magnitudes during the dry season (mean = 2.54 m) compared with the rainy season (mean = 2.39 m). Daily mean ionospheric delays ranged from 0.10 m to 3.70 m, while positioning accuracy metrics varied accordingly (2DRMS = 3.95–6.91 m; CEP = 1.64–2.89 m; SEP = 3.49–5.48 m; MRSE = 4.47–7.41 m). Moderate positive correlations (r = 0.29–0.36) between ionospheric delay and these accuracy indices confirmed that delay fluctuations degrade positioning precision. The findings demonstrate that ionospheric delay remains an important source of error for GNSS users in equatorial regions.