Abstract
The Advanced Himawari Imager (AHI) aboard the Himawari-8, a new generation of geostationary meteorological satellite, has high-frequency observation, which allows it to effectively capture atmospheric variations. In this paper, we have proposed an Improved Bi-angle Aerosol optical depth (AOD) retrieval Algorithm (IBAA) from AHI data. The algorithm ignores the aerosol effect at 2.3 μm and assumes that the aerosol optical depth does not change within one hour. According to the property that the reflectivity ratio K of two observations at 2.3 μm does not change with wavelength, we constructed the equation for two observations of AHI 0.47 μm band. Then Particle Swarm Optimization (PSO) was used to solve the nonlinear equation. The algorithm was applied to the AHI observations over the Chinese mainland (80°–135°E, 15°–60°N) between April and June 2019 and hourly AOD at 0.47 μm was retrieved. We validated IBAA AOD against the Aerosol Robotic Network (AERONET) sites observation, including surrounding regions as well as the Chinese mainland, and compared it with the AHI L3 V030 hourly AOD product. Validation with AERONET of 2079 matching points shows a correlation coefficient R = 0.82, root-mean-square error RMSE = 0.27, and more than 62% AOD retrieval results within the expected error of ±(0.05 + 0.2 × AODAERONET). Although IBAA does not perform very well in the case of coarse-particle aerosols, the comparison and validation demonstrate it can estimate AHI AOD with good accuracy and wide coverage over land on the whole.
Highlights
Aerosols are solid and liquid particles suspended in the atmosphere with a particle size between 0.001 and 100 μm
Mei et al (2012) utilized the k-ratio approach (k-ratio is the ratio of surface reflectance for two subsequent observations, which was approximated by the ratio of the reflectance at 1.6 μm) and time-series technique for joint retrieval of Aerosol optical depth (AOD) and aerosol type from Meteosat SecondGeneration (MSG)/Spinning Enhanced Visible and InfraRed Imager (SEVIRI) [16]
The 0.47 μm band is more sensitive to aerosols because it samIt is assumed that AOD does not change in the observation interval of one hour, which ples a part of the electromagnetic spectrum where clear-sky atmospheric scattering is imis consistent with the verification of ground stations [40]
Summary
Aerosols are solid and liquid particles suspended in the atmosphere with a particle size between 0.001 and 100 μm. Zhang et al (2011) applied the MAIAC algorithm to GOES observation and obtained the surface bidirectional reflectance distribution function and AOD [15]. Mei et al (2012) utilized the k-ratio approach (k-ratio is the ratio of surface reflectance for two subsequent observations, which was approximated by the ratio of the reflectance at 1.6 μm) and time-series technique for joint retrieval of AOD and aerosol type from MSG/SEVIRI [16]. For Himawari-8 AHI AOD, the famous DT algorithm was tested and produced a good result [21,22,23] She et al (2018) obtained the hourly AOD and surface reflectance by the OE method [24].
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