Aerosol Optical Depth Retrievals from High-Resolution Commercial Satellite Imagery Over Areas of High Surface Reflectance

摘要

The advancement and proliferation of high-resolution commercial imaging satellites presents a new opportunity for overland aerosol characterization. Current aerosol optical depth retrieval methods typically fail over areas with high surface reflectance, such as urban areas and deserts, since the upwelling radiance due to scattering by aerosols is small compared to the radiance resulting from surface reflection. The method proposed here uses shadows cast on the surface to exploit the differences between radiance from the adjacent shaded and unshaded areas of the scene. Given uniform surface reflectance for the shaded and unshaded areas, the difference in reflected radiance measured by a satellite sensor is related to the direct transmission of solar radiation and inversely proportional to total optical depth. Using an iterative approach, surface reflectance and mean aerosol reflectance can be partitioned to refine the retrieved total optical depth and, ultimately, determine the aerosol optical depth. Initial results based on QuickBird imagery and AERONET data collected during the UAE2 campaign, as well as archive imagery and AERONET data for four other cities, indicate that aerosol optical depth retrievals are possible in the visible and near-infrared region with an uncertainty of +or- 0.04 for areas with surface reflectance values of 0.15 (15%) or greater.