Sounding the earth's atmospheric water vapour using signals emitted by Global Navigation Satellite Systems

(eng) Global Navigation Satellite System (GNSS) are used to determine positions. As GNSS signals traverse the atmosphere, they undergo refraction, which is a disturbance that needs to be eliminated to allow high-accuracy positioning. However, when using stations with accurately known positions, the tropospheric path delay induced by the neutral atmosphere can be retrieved and provides valuable information to study the atmospheric water vapour for meteorological and climate applications. In this thesis, a GNSS analysis method was developed to estimate in near real-time tropospheric Zenith Path Delays (ZPD) from a European network of GNSS stations which comply with all requirements imposed by operational meteorology. Today, the method is applied to provide a service within the EUMETNET GNSS Water Vapour Program (E-GVAP). ZPD are estimated every 15 min, with a precision of about 5mm, a reliability score above 99% and are assimilated by meteorological agencies in their numerical weather prediction models. The method was further applied to observations from the Belgian dense GPS network during a severe thunderstorm to reconstruct the 2-D water vapour field over Belgium. The analysis showed that adding observations from GNSS densification networks on top of the European one is mandatory to monitor small-scale water vapour structures. Modernised GNSS and the new European Galileo system will provide us in the future with more signals of better quality and better observation geometry. A full multi-GNSS analysis will improve the precision and reliability of the ZPD estimates, the monitoring of small-scale water vapour structures and open new fields of meteorological applications.