Tropospheric water vapor retrievals by Ground-Based GNSS in Africa: A systematic review

Tropospheric water vapor is a complex parameter due to its spatial and temporal variability, but it is essential for meteorology and study of climate. Faced with high operating costs and traditional low resolutions, Ground-Based Global Navigation Satellite System (GNSS) is increasingly used for tropospheric water vapor retrieval. From databases and several query strings, this study examines in different ways the evidence-based studies of water vapor retrieval from African Ground-Based GNSS using the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) protocol and specific criteria. 30 articles of empirical studies published between 2000 and June 2024 were analysed in depth vis-a-vis research questions. This Systematic Review (SR) includes a mapping of the selected literature, highlighting the distribution and focus of research efforts across Africa. This SR provides new insights by consolidating the evidence on the various approaches used with African Ground Stations. Water vapor time series obtained from GNSS data show consistency with traditional data sources, particularly for seasonal and diurnal cycles. It also highlights the under-exploited potential of GNSS networks in Africa, limited by uneven geographical coverage and a lack of standardization of methodologies, despite significant progress in atmospheric studies, as well as it highlights the advanced techniques that are under-exploredand proposes future research directions, while calling for closer collaboration between scientists and decision-makers to improve access to GNSS data, promote network interoperability, and explore methodological approaches adapted to Africa’s specific climatic conditions, in order to maximise the applications of GNSS techniques for water vapor retrieval.