Evaluating the Accuracy of Jason-3 Water Vapor Product Using PWV Data From Global Radiosonde and GNSS Stations

Jason-3 is equipped with the Advanced Microwave Radiometer-2 (AMR-2) to account for the zenith wet delay (ZWD) caused by the troposphere in the altimeter signal, from which the precipitable water vapor (PWV) can be deduced. In order to investigate the accuracy of PWV from Jason-3 AMR-2 on a global scale, we adopted PWV observations from 263 radiosonde stations and 103 Global Navigation Satellite System (GNSS) stations as reference PWV. These reference PWVs are recorded during Jason-3 cycles 0-119 and are globally distributed in coastal and island regions. Over 60 000 Jason-3 PWV versus radiosonde PWV comparison points and over 380 000 Jason-3 PWV versus GNSS PWV comparison points are used in this study. For GNSS PWV, two PWV height reduction methods (Kouba empirical method and European Centre for Medium-Range Weather Forecasts (ECMWF) method) are used to reduce the PWV from height of station to sea level. The comparison results indicate that the root-mean-square error (RMSE) of Jason-3 PWV evaluated using radiosonde PWV is 3.4 kg/m². Jason-3 PWV has an RMSE of 3.0 kg/m² with GNSS PWV derived using ECMWF PWV height correction, while the RMSE between Jason-3 PWV and GNSS PWV derived using Kouba PWV height correction is 3.1 kg/m². In addition, the accuracy of Jason-3 PWV increases when the latitude of its footprints or the distance from its footprints to land increases.