Abstract
Himawari-8, a next-generation geostationary meteorological satellite, was successfully launched by the Japanese Meteorological Agency (JMA) on 7 October 2014 and has been in official operation since 7 July 2015. The Advanced Himawari Imager (AHI) onboard Himawari-8 has 16 channels from 0.47 to 13.3 μm and performs full-disk observations every 10 min. This study describes AHI aerosol optical property (AOP) retrieval based on a multi-channel algorithm using three visible and one near-infrared channels (470, 510, 640, and 860 nm). AOPs were retrieved by obtaining the visible surface reflectance using shortwave infrared (SWIR) data along with normalized difference vegetation index shortwave infrared (NDVISWIR) categories and the minimum reflectance method (MRM). Estimated surface reflectance from SWIR (ESR) tends to be overestimated in urban and cropland areas. Thus, the visible surface reflectance was improved by considering urbanization effects. Ocean surface reflectance is obtained using MRM, while it is from the Cox and Munk method in ESR with the consideration of chlorophyll-a concentration. Based on validation with ground-based sun-photometer measurements from Aerosol Robotic Network (AERONET) data, the error pattern tends to the opposition between MRMver (using MRM reflectance) AOD and ESRver (Using ESR reflectance) AOD over land. To estimate optimal AOD products, two methods were used to merge the data. The final aerosol products and the two surface reflectances were merged, which resulted in higher accuracy AOD values than those retrieved by either individual method. All four AODs shown in this study show accurate diurnal variation compared with AERONET, but the optimum AOD changes depending on observation time.
Highlights
Aerosols have a direct effect on the Earth’s radiation balance and act as cloud condensation nuclei, which affects the efficiency of the reflection of solar radiation by clouds by changing cloud microphysical properties, and influences the dynamical development and precipitation efficiency of clouds [1,2]
Land surface reflectance was estimated from shortwave infrared (SWIR) in addition to existing Minimum Reflectance Method (MRM), and ocean reflectance was from Fresnel equations with the consideration of chlorophyll-a concentration, as discussed
Both fine mode fraction (FMF) and AE are related to aerosol size, and their values can be inter-compared to some extent in areas where aerosols are present
Summary
Aerosols have a direct effect on the Earth’s radiation balance and act as cloud condensation nuclei, which affects the efficiency of the reflection of solar radiation by clouds by changing cloud microphysical properties, and influences the dynamical development and precipitation efficiency of clouds [1,2]. Studies were carried out to obtain high spatial resolution data from MISR [14] Polarization measurement such as the Polarization and Directionality of the Earth’s Reflectances (POLDER) can increase the degree of freedom for signal, more accurate AOPs including size and absorptivity can be retrieved [15]. Geosynchronous earth orbit (GEO) satellites with high temporal resolution can provide information on aerosol transport, but have difficulty retrieving aerosol properties using previous sensors because they lack multiple channels in the visible region. The Geostationary Ocean Color Imager (GOCI) onboard the COMS is the first sensor in GEO to observe ocean color and has 6 visible channels that are useful for the retrieval of aerosol properties [23,24].
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