The MISR, MODIS, OMI, and POLDER instruments have demonstrated many new space-based passive aerosol remote sensing capabilities. These include aerosol optical thickness (AOT) to about 0.05 or 20% of the AOT over land, better-constrained results over dark water, and even some ability to measure AOT of smoke over cloud decks and dust over bright desert surfaces. Particle size distributions in two to five bins are produced under good, but not ideal, viewing conditions, spherical vs. non-spherical particle shapes are identified, and particle single-scattering albedo is constrained into two –to four bins over water and some land. In many cases, aerosol source plume and elevated absorbing aerosol layer heights can be derived as well. This is immense progress over previous satellite instruments, which were not designed for aerosol studies, and provided only limited AOT information, and nothing quantitative about aerosol microphysical properties.

The new global aerosol products from these satellite instruments are being used increasingly in regional aerosol impact analyses, and large-scale, long-term climate studies. But there remain some systematic differences among MISR, MODIS, and ground-based-AERONET-retrieved AOT and aerosol properties, even over water, where the retrievals are expected to perform best. Although the discrepancies are within the measured product uncertainties, the differences imply that we have not yet met the 0.02 or better mid-visible AOT precision, which translates into about 0.5 W/m2 sensitivity, as is required to address key climate aerosol radiative forcing questions.

We trace the systematic AOT discrepancies to algorithm spectral water-leaving reflectance assumptions, ocean near-surface wind speeds adopted, particle property constraints, cloud masking procedures, and calibration differences. We identify approaches to refining the current algorithms, and outline some ways next-generation aerosol missions could generate aerosol products capable of addressing an even more demanding set of aerosol-climate issues.

This work is performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.