A new way to obtain the weighted mean temperature (Tm): Using the Geostationary Interferometric Infrared Sounder (GIIRS) equipped on FengYun Satellite

Atmospheric weighted mean temperature (Tm) is an important parameter in the Global Navigation Satellite System (GNSS) meteorology, essential for retrieving precipitable water vapor (PWV). The FengYun-4 satellite (FY-4) carries Geostationary Interferometric Infrared Sounder (GIIRS), which realizes the transition from two-dimensional to three-dimensional detection of the vertical structure of the atmosphere in geostationary orbit, providing a more convenient and accurate data source for the inversion of Tm. The study presents a novel approach for deriving the Tm based on the GIIRS products of FengYun-4A satellite (FY-4A) and FengYun-4B satellite (FY-4B). The Tm calculated from the radiosonde data is utilized as reference to assess the performance of FY-4A and FY-4B, which demonstrates that the GIIRS equipped on FY-4 can provide a new way to obtain the Tm. The numerical results show that the mean absolute error (MAE) and root mean square error (RMSE) are 1.65/ 2.06 K and 1.38/ 1.73 K for FY-4A and FY-4B, respectively. The different performance of FY-4A and FY-4B on Tm are also observed from the analysis of the geographical distribution, seasons and epochs. Specifically, the RMSE distribution of FY-4A at different stations ranges from 1.08 to 3.47 K, while the distribution of FY-4B is more concentrated between 1.37 and 2.70 K. The accuracy of FY-4 A deteriorates as increasing latitude, while the phenomenon is not obvious for FY-4B. Moreover, FY-4 A performs slightly better at UTC 0:00 than at UTC 12:00, while FY-4B has a slightly better performance in autumn than in other seasons.