Retrieval and validation of diurnal properties of aerosol and surface from geostationary satellite Himawari-8 using multi-pixel approach

Abstract. The Advanced Himawari Imager (AHI) onboard the Himawari-8 geostationary satellite is an imager with 16 spectral bands covering from the visible to infrared. The AHI has high temporal resolution with observation frequency of every 10 min and high spatial resolution 0.5–2 km (depending on channel) for full disk, which provides great potential for studying the dynamics of aerosol properties in East Asia and Western Pacific regions. In this study, the development of aerosol and surface property retrievals from the AHI/Himawari-8 using the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm is described. Due to the pseudo multi-angular observations obtained from AHI/Himawari-8 and the flexibility of GRASP algorithm with its innovative multi-pixel concept, multiple time and spatial pixels were retrieved simultaneously with both aerosol and surface properties constrained between the pixels together with additional constraints on spectral variability of underlying surface parameters within each pixel. The developed GRASP based algorithm has been applied to AHI/Himwari-8 observations over land for the entire year of 2018, and over ocean for May 2018 only, due to computational resource limitations and the relatively lower complexity of aerosol retrievals over ocean. The generated retrieval products were validated against the Aerosol Robotic Network (AERONET) measurements and were also intercompared with the Moderate Resolution Imaging Spectroradiometer (MODIS) surface products. Overall, the validation analysis shows robust agreement of AHI/GRASP spectral AOD product with AERONET with correlation coefficients of 0.82–0.93 across the spectrum over land. The AHI/GRASP results demonstrate encouraging agreement with AERONET that is with 34.4 % of the AOD (510 nm) satisfying the Global Climate Observing System (GCOS) requirement, and a bias within ±0.02 for AOD over land. The validation for fine and coarse mode AOD also showed promising results with a correlation of 0.89 and mean bias of 0.04 for fine mode AOD when compared with AERONET measurements. As for the intercomparisons with MODIS products, the overall performance is quite comparable to MODIS surface products. In addition to the analysis of AHI/Himawari-8 alone retrieval, this study demonstrated a novel synergetic retrieval between AHI/Himawari-8 and micro-pulse lidar (MPL). Using this synergy resulted in further improvements of the aerosol retrievals especially over the low AOD conditions due to the improved sensitivity to aerosol.