Abstract: [Purposes] To evaluate the impact of IGU and IGF precise ephemerides provided by the International GNSS Service on the accuracy of global navigation satellite system (GNSS)-based precipitable water vapor (PWV)retrieval. [Methods] Based on the principles of GNSS water vapor remote sensing,RTKLIB was used to process observational data from eight representative stations in the multi-GNSS experiment (MGEX)tracking network for January 2024.Using PWV from ERA5 reanalysis data as a benchmark,the retrieval results from the two ephemerides were quantitatively compared through mean bias,root mean square error (RMSE),standard deviation,and correlation coefficient. [Findings] The results indicate that the IGF ephemeris yields higher overall accuracy for PWV retrieval,with RMSE and standard deviation both at 1.9 mm,outperforming the IGU ephemeris (2.1 mm).The PWV retrieval accuracy shows significant latitudinal variation,with higher accuracy in mid-to-high latitude regions (RMSE approximately 1.4 mm)compared to regions near the equator (RMSE approximately 2.5 mm).The temporal variation of PWV is closely related to rainfall events,with rapid short-term increases (e.g.,exceeding 5 mm)often followed by rainfall. [Conclusions] This study demonstrates that the IGF ephemeris offers higher reliability in PWV retrieval.GNSS-based PWV retrieval not only reflects the spatiotemporal distribution characteristics of water vapor but also provides valuable information for short-term and imminent rainfall forecasting,offering insights to promote the operational application of GNSS water vapor remote sensing.

Key words: GNSS, ERA5 reanalysis data, water vapor retrieval, IGS orbits (IGU/IGF), PWV, rainfall forecasting