Evaluation of the FY-4B/AGRI land aerosol optical depth product and comparison with geostationary satellite products over Asia

The land aerosol optical depth (AOD) based on the Advanced Geostationary Radiation Imager (AGRI) aboard Fengyun-4B (FY-4B) has been officially released since August 2022. The initial operational product was based on the Dark Target (DT) algorithm and has been previously evaluated. A new land AOD product was subsequently developed under an improved Deep Blue (DB) framework with an hourly surface reflectance prior database, broadly consistent with the retrieval approaches of the Advanced Himawari Imager (AHI) aboard Himawari-9 and the Geostationary Environment Monitoring Spectrometer (GEMS) aboard GK-2B, this study evaluates the FY-4B/AGRI DB-based AOD and compares with the AHI and GEMS products. Results show that the AGRI AOD achieves the highest accuracy (R = 0.840, RMSE = 0.175) relative to AHI (R = 0.765, RMSE = 0.217) and GEMS (R = 0.707, RMSE = 0.214), with 57.66% within the Expected Error envelope (EE = ±(0.05 + 0.20τ)), ranking between AHI (56.19%) and GEMS (59.38%). The AGRI AOD maintains relatively stable retrieval errors across different vegetation-index ranges, where the accuracy of AHI and GEMS is limited. In terms of geometric sensitivity, the AGRI AOD degrades at viewing zenith angles above 56°, while AHI errors increase markedly when SZA is below 15°, and GEMS shows larger variability. These findings confirm the competitive accuracy of the FY-4B DB-based AOD on the international stage and provide quantitative guidance for future multi-satellite aerosol product fusion.