Multi-epoch assessment of static multi-GNSS precise point positioning performance across African IGS stations

Abstract

This study evaluates the spatial and temporal performance of static multi-GNSS Precise Point Positioning (PPP) solutions across twelve selected African International GNSS Service (IGS) stations representing diverse geographic and ionospheric environments. Using observations from the years 2013, 2018, and 2023, data were processed via the PPP-A software package (v2024.1) using dual-frequency ionosphere-free linear combinations. Coordinate differences were transformed into a local topocentric East, North, and Up (ENU) frame to accurately assess the impact of regional atmospheric delay and reference frame consistency on positioning precision. The empirical results reveal that the apparent coordinate residuals are heavily contaminated by long-term tectonic displacements of the Nubian and Somalian plates – accumulating up to several decimeters over the ten-year baseline – rather than reflecting pure PPP algorithm stochastic errors. True static PPP residuals maintained sub-decimeter geodetic precision once geophysical plate motion and terrestrial reference frame evolutions (IGS14/IGS20) were properly aligned. Statistical assessments using non-parametric Friedman tests and linear mixed-effects models confirm that spatial environmental variations and station-specific atmospheric tracking conditions significantly override temporal drift across the evaluated epochs. While multi-constellation PPP remains a highly reliable tool for geodetic infrastructure in sparse networks, this study highlights that isolating geophysical signals from operational processing artifacts is essential for meaningful accuracy assessments in the African continent.