Evaluating Aerosol Optical Depth Retrieved From VIIRS Using Global Scale, Multi‐Seasonal Airborne Observations

Abstract

AbstractAerosol optical depth (AOD) is a vital parameter in atmospheric research. Using observations of the Visible Infrared Imaging Radiometer Suite (VIIRS), onboard Suomi National Polar‐orbiting Partnership (Suomi‐NPP) and NOAA‐20 satellites, National Oceanic and Atmospheric Administration (NOAA) produces near‐real time AOD product with high pixel resolution (750 m), wide swath width (3,040 km), and a 16‐day repeat cycle. Here we report the evaluation of the NOAA/VIIRS AOD using a comprehensive aerosol data set, derived from a global‐scale, multi‐seasonal airborne mission, the NASA Atmospheric Tomography Mission (ATom). This data set includes rich physical and chemical information, such as size distributions, chemical compositions, optical properties, and hygroscopicities of major aerosol types, including dust, sea salt, smoke, internally mixed sulfate/nitrate/organics particles (non‐smoke), black carbon, etc. Globally, VIIRS AOD (Suomi‐NPP and NOAA‐20) shows good agreement with the ATom AOD in the moderate to high AOD range (>0.3), with respect to measurement uncertainties (orthogonal distance regression fitting slope: 1.5 ± 0.2 for Suomi‐NPP and 1.6 ± 0.5 for NOAA‐20; correlation coefficient: 0.85 for Suomi‐NPP and 0.73 for NOAA‐20). There is a persistent bias in the low AOD range (<0.3) on the order of 0.03, likely reflecting systematic errors on VIIRS and/or the ATom AOD product. Ångström exponent reported by VIIRS shows excellent agreement with ATom results within expected uncertainties. Given the unique insights revealed by the ATom AOD and aerosol property data set, it is desirable to have ATom‐like comprehensive payloads in future airborne satellite validation programs.