MODTRAN-based Retrieval of Aerosol Optical Thickness over Chiba Area from Himawari-8/AHI visible images

摘要

Atmospheric aerosol has a pivotal role in both air-pollution and radiation budget studies. In this paper, we retrieve the spatial distribution of aerosol optical thickness (AOT) over Chiba Area from daytime images of Himawari-8 geostationary satellite. The concurrent data from ground-based measurements are used in the analysis, namely the temporal variation of AOT from a sunphotometer and sky-radiometer located at the Center for Environmental Remote Sensing (CEReS), Chiba University. Also, the information on vertical profiles of aerosols and clouds is obtained from the data of NIES (National Institute for Environmental Studies) lidar operated also on the campus of Chiba University. We employ the MODTRAN (MODerate resolution atmospheric TRANsmission) radiative transfer code for simulating the radiance components that reach the AHI sensor onboard the satellite. The retrieval of AOT is based on look-up tables (LUTs) that are calculated for plausible values of both AOT and the surface reflectance for each of the AHI bands. The choice of aerosol model is optimized with the help of sunphotometer and sky-radiometer data coupled with the surface-based weather and aerosol sampling data. Additional information that is available from the present approach is the influence of thin clouds such as cirrus, since the discrimination of aerosol and cirrus effects is usually a difficult task in most of the atmospheric correction studies. We discuss the seasonal changes of AOT and surface reflectance from the present analysis based on LUTs. It is demonstrated that for each season, the satellite data observed on a clear day with minimum aerosol loading can be used to establish a good reference for the analysis of various satellite data such as MODIS or Landsat to evaluate the AOT distribution over the Chiba area.