Operational Aerosol Optical Mapping from Remotely-sensed Data over Land Surface in China

The atmosphere contains solid and liquid particles (aerosols) and clouds, which interact with the incoming and outgoing radiation in a complex and spatially very variable manner. Aerosol particles are a largely natural, though highly variable, component of our atmosphere. Aerosols affect our environment at the local, regional, and global levels. There are many factors that are known to influence climate, both natural and human-induced. The increase in concentrations of greenhouse gases and aerosols through human activity is of particular concern. The effect of the increasing amount of aerosols on the radiative forcing is not yet well known. Regional patterns of climate change depend significantly on the time dependence of the forcing, the spatial distribution of aerosol concentrations and details of the modelled climate processes. Determination of aerosol optical depth from satellite remote sensing measurements is extremely complex due to the large variability of aerosol optical properties. Significant simplification occurs when measurements are taken over water since the ocean reflection signal can be taken as negligible in the near infrared. Unfortunately, over land, most of the signal can be attributed to ground reflectance. In this paper we propose a new approach to retrieve aerosol properties over land surfaces, especially high reflectance surface including arid, semiarid, and urban areas, where the surface reflectance is usually very bright in the red part of visible spectrum and in the near infrared, but is much darker in the blue spectral region. The quantitative retrieval of aerosol optical thickness from satellite data for land surface has been successfully conducted in China using MODIS and AATSR data. The results agreed with AERONET in situ measurement very well with averaged relative error less than 10%. The algorithm developed makes full use of the high frequency multi-temporal information and multi-spectral information from MODIS and AATSR, without any a prior knowledge of the underlying land surface characteristics. Fused with the national aerosol measurement network data, the national AOT map can be produced at 5km spatial resolution on the daily base. This national climate aerosol optical thickness data will be useful for the research of regional response to the global climate change.