Remote Sensing of Tropospheric Aerosols from Space: Past, Present, and Future

Tropospheric aerosol particles originate from man-made sources such as urban/industrial activities, biomass burning associated with land use processes, wind-blown dust, and natural sources. Their interaction with sunlight and their effect on cloud microphysics form a major uncertainty in predicting climate change. Furthermore, the lifetime of only a few days causes high spatial variability in aerosol optical and radiative properties that requires global observations from space. Remote sensing of tropospheric aerosol properties from space is reviewed both for present and planned national and international satellite sensors. Techniques that are being used to enhance our ability to characterize the global distribution of aerosol properties include well-calibrated multispectral radiometers, multispectral polarimeters, and multiangle spectroradiometers. Though most of these sensor systems rely primarily on visible to near-infrared spectral channels, the availability of thermal channels to aid in cloud screening is an important additional piece of information that is not always incorporated into the sensor design. In this paper, the various satellite sensor systems being developed by Europe, Japan, and the United States are described, and the advantages and disadvantages of each of these systems for aerosol applications are highlighted. An important underlying theme is that the remote sensing of aerosol properties, especially aerosol size distribution and single scattering albedo, is exceedingly difficult. As a consequence, no one sensor system is capable of providing totally unambiguous information, and hence a careful intercomparison of derived products from different sensors, together with a comprehensive network of ground-based sunphotometer and sky radiometer systems, is required to advance our quantitative understanding of global aerosol characteristics.