Accuracy evaluation of FY-4B GIIRS temperature and relative humidity profile products

FY-4B represents the first operational satellite within the Fengyun-4 series, launched by China. Evaluating the accuracy of the FY-4B Geostationary Interferometric Infrared Sounder (GIIRS) temperature (T) and relative humidity (RH) profile products is crucial for the advancement and practical deployment of China’s geostationary satellite hyperspectral data. This study assesses the detection capabilities and accuracy of the FY-4B T and RH profile products relative to FY-4A, utilizing radiosonde data spanning from January 16, 2023, to January 16, 2024. The findings indicate that the FY-4B GIIRS demonstrates comparable capabilities in detecting T under clear skies to the FY-4A GIIRS. However, the FY-4A GIIRS exhibits superior performance in cloudy conditions. While FY-4B GIIRS effectively detects RH, its RH profile products show less accuracy, with a bias of -3.89%, an RMSE of 15.42%, and a correlation coefficient (CC) of 0.56. In contrast, the FY-4B T profile product shows a bias of -0.44°C, an RMSE of 2.05°C, and a CC of 0.89, indicating an overall higher accuracy compared to the FY-4A T profile product, which has a bias of -0.46°C, an RMSE of 2.26°C, and a CC of 0.87. Despite their overall minor deviation from radiosonde measurements, the correlation with radiosonde data inversely correlates with station altitude. Notably, due to the observation zenith angle in Xinjiang exceeding 60 degrees even before FY-4B’s drift, the satellite lacks T and RH profile products in Xinjiang and parts of the northwestern region under clear skies during the study period. Overall, the T profile products from FY-4A/B exhibit high accuracy and effectively address the scarcity of meteorological observations in remote areas.