Evaluation of Global VIIRS Aerosol EDR Product with MODIS and AERONET

The aerosol environmental data record (EDR) is the primary aerosol product from the Suomi-NPP Visible and Infrared Imaging Radiometer Suite (VIIRS). It contains the Aerosol Optical Thickness (AOT) at 0.55 μm and center wavelengths of bands M1-M8 and M10-M11 (0.412, 0.445, 0.488, 0.555, 0.672, 0.746, 0.865, 1.24, 1.61, and 2.25 μm), Angström Exponent (AE) at 0.445/0.672 μm over land and 0.865/1.61 μm over ocean, small mode fraction over ocean, and associated quality flags (AOT quality, AE quality, land/water, cloud contamination, cloud adjacent, cirrus, bad reflectance, sunglint, cloud shadow, snow/ice, fire, low sun, bright surface, etc.). The VIIRS aerosol retrieval is performed at moderate resolution pixel level (~0.75 to 1.6 km from nadir to edge), and VIIRS EDR is aggregated from 8x8 pixels at ~6 to 12.8 km resolution which allows for full global coverage without any gaps. In this study, global statistics (mean, standard deviation, etc.) of VIIRS aerosol EDR products are analyzed as a function of surface type (land, water), latitude zone and geometry (solar zenith, viewing zenith and scattering angle) by comparing with those of MODIS (Aqua) level 2 Collection 5.1 aerosol retrievals to investigate the general agreement of these two global products. It is found that the global AOT patterns are similar between VIIRS and MODIS, but VIIRS significantly overestimates AOT over land (by ~50%) and underestimates AOT over dust outflow areas over ocean. In addition, VIIRS tends to retrieve higher small mode fraction and thus higher AE over ocean. These global difference are persistent throughout the period studied. Evaluation of VIIRS and MODIS aerosol retrievals against AERONET level 1.5 direct-Sun measurements was also performed to help understand the difference between VIIRS and MODIS retrievals. Potential algorithm improvements based on these analyses will also be presented.