Assessing Real-Time PPP Performance for PWV Estimation Using Low-Cost GNSS Stations and Multi-Source Correction Products

Monitoring atmospheric water vapour is essential for weather forecasting and climate studies. GNSS networks can retrieve Precip- itable Water Vapour (PWV) continuously at each station location, but the accuracy depends on the quality of the satellite orbit and clock corrections used in the processing. This study evaluates PWV retrieval from 478 stations of the French Centipede low-cost GNSS network using four levels of correction products with decreasing latency: GFZ Final (∼2 weeks), Rapid (∼1 day), Ultra-rapid (3–9 hours), and broadcast ephemerides (real-time). Validation against ERA5 reanalysis shows that the Final and Rapid products achieve similar performance (RMSE ≈ 2 mm, r2 = 0.84), confirming that near-real-time processing introduces no significant accur- acy loss. Ultra-rapid products remain usable (RMSE = 3.4 mm), while broadcast ephemerides show larger errors (RMSE = 5.8 mm) but still capture the spatial moisture pattern. In addition, a real-time experiment using the freely available Galileo High Accuracy Service (HAS) demonstrates that stable tropospheric estimates (ZTD ± 1.4 mm, PWV ± 0.2 mm) can be obtained in real time, even before the positioning solution has fully converged. These results suggest that combining the spatial density of low-cost networks with real-time HAS corrections could enable high-resolution PWV monitoring that is not achievable with existing systems.