Toward unified satellite climatology of aerosol properties: What do fully compatible MODIS and MISR aerosol pixels tell us?

Because of the global nature of aerosol effects on climate, satellite observations have been and will be an indispensable source of information about aerosol characteristics for use in various assessments of climate and climate change. There have been parallel claims of unprecedented accuracy of aerosol retrievals with the moderate-resolution imaging spectroradiometer (MODIS) and multiangle imaging spectroradiometer (MISR). These claims have been based on limited comparisons with ground-based observations which, however, are not necessarily indicative of the actual global performance of these satellite sensors. Fortunately, both instruments have been flown for many years on the same Terra platform, which provides a unique opportunity to compare fully collocated pixel-level MODIS and MISR aerosol retrievals directly and globally. Our present extensive analysis of 8 years of the MODIS-Terra and MISR aerosol data documents unexpected significant disagreements at the pixel level as well as between long-term and spatially averaged aerosol properties. The only point on which both datasets seem to fully agree is that there may have been a weak increasing tendency in the globally averaged aerosol optical thickness (AOT) over the land and no long-term AOT tendency over the oceans. Overall our new results suggest that the current knowledge of the global distribution of the AOT and, especially, aerosol microphysical characteristics remains unsatisfactory.