Consistent Long-Term Aerosol Data Records over Land and Ocean from SeaWiFS

The impact of natural and anthropogenic sources of air pollution has gained increasing attention from scientific communities in recent years. Indeed, tropospheric aerosols not only perturb the radiative energy balance by interacting with solar and terrestrial radiation, but also by changing cloud properties and lifetime. Due to their relatively short lifetime (a few hours to about a week), the distributions of these airborne particles vary extensively in both space and time. Consequently, satellite observations are needed over both source and sink regions for continuous temporal and spatial sampling of aerosol properties. With the advent of the new generation of EOS era satellite sensors in the 1990s, a well-calibrated, accurate long-term aerosol dataset from satellite measurements is now becoming possible. Such a dataset is a critical component in performing the quantitative evaluations of aerosol variability on a global basis that are needed to form a consensus among the scientific community and policy makers regarding the role of aerosols in modifying the global radiative budget due to anthropogenic activities. In this paper, we will demonstrate the capability of a new satellite algorithm to retrieve aerosol properties over ocean and land, including bright-reflecting surfaces such as urban areas and deserts. Aerosol retrievals over such regions have been difficult to perform using previously available algorithms that use wavelengths from the mid-visible to the near IR because it is difficult to separate aerosol signal from the contribution due to the bright surface reflectance. The new algorithm, called Deep Blue, utilizes blue-wavelength measurements from instruments such as SeaWiFS and MODIS to infer the properties of aerosols, since the surface reflectance over land in the blue part of the spectrum is much lower than for longer wavelength channels. The preliminary datasets of aerosol products since 1997 from SeaWiFS have been generated using Deep Blue algorithm and their evaluations are under way. We will investigate the inter-annual variability of source and pathway of aerosols over different regions, based upon these data sets of more than 10 years. The monthly averaged aerosol optical thickness from SeaWiFS will also be compared with the MODIS Deep Blue products for the overlapping years. The validation of these SeaWiFS retrieved aerosol optical thickness with data from AERONET sun-photometers will also be discussed. These new satellite products will allow scientists to deter-mine quantitatively the aerosol properties near sources, pathways, and sinks using high spatial resolution measurements from SeaWiFS and MODIS-like instruments.