Development of an aerosol optical depth retrieval algorithm based on an improved scattering angle scheme for Advanced Himawari Imager observations

The Advanced Himawari Imager carried by the Himawari-8/9 geostationary satellite provides an effective tool for high-temporal-resolution aerosol monitoring with 10-min temporal resolution. Aerosol optical depth (AOD), as a crucial parameter for characterizing aerosols, is typically retrieved using physical-based algorithms that rely on prior assumptions about surface reflectance and aerosol models. However, these assumptions may not satisfy the complex land and atmospheric circumstances. This study develops a new AOD retrieval algorithm that improves the accuracy of surface reflectance and aerosol model by leveraging the time-series geostationary observations and aerosol properties clustered from precise ground-based measurements. AOD retrievals for 2022 to 2023 were conducted for southern China (mainly in Guangdong province), and validated against ground measurements from AErosol RObotic NETwork (AERONET) and Sun-sky radiometer Observation NETwork (SONET). The results are also compared with aerosol products from the MODerate resolution Imaging Spectroradiometer (MODIS). The retrieval results showed high consistency with AERONET/SONET, achieving a correlation coefficient of 0.74, RMSE of 0.18, and over 52 % of retrievals within the expected error envelopes (EE) of ±(0.05 + 15 %). In comparison, the Japan Aerospace Exploration Agency (JAXA) AOD products have a lower correlation coefficient of 0.232, RMSE of 0.330, and only about 30 % of retrievals within the EE of ±(0.05 + 15 %). Furthermore, the proposed algorithm outperforms MODIS in terms of accuracy over their common retrievals. The algorithm based on a newly developed scattering scheme improves the retrieval accuracy at different times and can show aerosol diurnal variations in south China.