Controlling factors analysis for the Himawari-8 aerosol optical depth accuracy from the standpoint of size distribution, solar zenith angles and scattering angles

This work aims at providing a novel controlling factors analysis for the Advanced Himawari Imager (AHI) AOD retrieval from the aspect of particle size distribution and Sun-Earth-Satellite geometries, through combining the high quality ground-based observation in Wuhan. The three-years co-located AOD dataset of AHI and sun-photometer in Wuhan are used to support this work. AHI overall underestimates AOD over Wuhan site with coefficient of determination (R2) equal 0.7. Though the best retrieval appeared in summer, underestimation is found to be persistent in each season. Combining with the characteristics of aerosol hygroscopic growth in Wuhan, we found the fine-mode particle median radius which supposed by AHI is lower than the in-site measurement. This leads to the overestimation of back scattering by aerosol particles, and induces underestimation of AOD consequently. The correlation and bias analyses of AOD with respect to the variation of Solar Zenith Angle and scattering angles are also performed. Phase function derived by sun-photometer is applied to discuss the influence of scattering angle on AOD inversion. Accompany with the scattering angle, the AOD retrieval bias consistently varies with the phase function bias, which further confirm the impact of phase function on AHI retrieval. Finally, the dark target method was applied to retrieve AHI AOD. The comparison results show that dark target overestimated AOD and performed worse in Wuhan. It could reveals that AHI aerosol retrieval method has some advantages in heavy aerosol loading places without enough prior information of aerosol properties.