Multiangle Imaging SpectroRadiometer global aerosol productassessment by comparison with the Aerosol Robotic Network

摘要

A statistical approach is used to assess the quality of the Multiangle ImagingSpectroRadiometer (MISR) version 22 (V22) aerosol products. Aerosol optical depth(AOD) retrieval results are improved relative to the early postlaunch values reported by[Kahn et al. (2005)], which varied with particle type category. Overall, about 70% to 75% of MISR AOD retrievals fall within 0.05 or20% x AOD of the paired validation data from the Aerosol Robotic Network(AERONET), and about 50% to 55% are within 0.03 or 10% x AERONET AOD, exceptat sites where dust or mixed dust and smoke are commonly found. Retrieved particlemicrophysical properties amount to categorical values, such as three size groupings:"small," "medium," and "large." For particle size, ground-based AERONET sunphotometer Angstrom exponents are used to assess statistically the corresponding MISRvalues, which are interpreted in terms of retrieved size categories. Coincident single-scattering albedo (SSA) and fraction AOD spherical data are too limited for statisticalvalidation. V22 distinguishes two or three size bins, depending on aerosol type, and abouttwo bins in SSA (absorbing vs. nonabsorbing), as well as spherical vs. nonsphericalparticles, under good retrieval conditions. Particle type sensitivity varies considerably withconditions and is diminished for midvisible AODs below about 0.15 or 0.2. On the basis ofthese results, specific algorithm upgrades are proposed and are being investigated by theMISR team for possible implementation in future versions of the product.