The precipitable water vapor products from the FY-4B satellite were compared with ground-based radiosonde and GNSS data across mainland China.

Data Summary: FY-4B water vapor products were validated by both radiosonde and GNSS data. Radiosonde and GNSS data from January 1, 2024 to December 31, 2024 provided by the China Meteorological Administration (CMA). Radiosonde data was obtained twice a day (i.e., 00UTC and 12 UTC), including 123 stations. GNSS data was obtained per minute at each station. There were 1453 GNSS stations used for this study. All the GNSS stations were equipped with meteorological sensors that provided the essential measurements of temperature, pressure, and relative humidity required for calculating PWV. Data Processing: Radiosonde observations were available at 00 UTC and 12 UTC, while FY-4B PWV was provided every 15 minutes. The GNSS PWV was originally retrieved at 1-minute intervals. The GNSS and radiosonde PWV data were matched with site identity. The spatial matching between the FY-4B data with radiosonde and GNSS data use nearest neighbor. For each station, the FY-4B pixel whose center coordinates (latitude and longitude) were closest to the station location was identified, and the corresponding PWV value was extracted. The temporal matching of the three PWV data products was conducted using a 30-minute window.