Remote sensing of tropospheric aerosols from space: Past, present, and future

Tropospheric aerosol particles originate from man-made sources such as urba n/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 sp atial variability in aerosol optical and radiative properties that requires global observations from space. Remote sensing of tropospheric aerosol properties from space is reviewed bo th for present and planned national and international satellite sensors. Te chniques that are being used to enhance our ability to characterize the glo bal distribution of aerosol properties include well-calibrated multispectra l radiometers, multispectral polarimeters, and multiangle spectroradiometer s. Though most of these sensor systems rely primarily on visible to near-in frared spectral channels, the availability of thermal channels to aid in cl oud screening is an important additional piece of information that is not a lways incorporated into the sensor design. In this paper, the various satel lite sensor systems being developed by Europe, Japan, and the United States are described, and the advantages and disadvantages of each of these syste ms for aerosol applications are highlighted. An important underlying theme is that the remote sensing of aerosol properties, especially aerosol size d istribution and single scattering albedo, is exceedingly difficult. As a co nsequence, 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 su nphotometer and sky radiometer systems, is required to advance our quantita tive understanding of global aerosol characteristics.