Regional Trends in Aerosol Optical Depth During the 20-Year MODIS Mission

Abstract:

Aerosol optical depth (AOD) retrievals from the NASA Dark Target (DT) algorithm began with the launch of MODIS Terra in 2000, added a second sensor with MODIS Aqua in 2002, and continue through the present day. The DT algorithm has also been adapted for VIIRS, and development is underway for geostationary imagers such as ABI and AHI. Although continuity with these additional instruments is necessary to keep the measurements going long enough to form a climate data record, coherent regional trends in AOD have emerged since the beginning of the MODIS record, with good agreement between MODIS Terra and MODIS Aqua during the 18 years that both sensors have been in service. Since 2012, the DT product for VIIRS SNPP has shown similar agreement in shorter-term changes to AOD. Some of these trends, such as the reduction in AOD over much of the industrialized world, likely result from policy changes over the first two decades of the 21^st century. Others, such as the small but widespread increase in AOD over the Southern Ocean, require more investigation to determine a cause.

Figure. Regional change in AOD per year for MODIS Aqua since June 2002 (the beginning of the Aqua record), where 1°×1° grid cells meet a significance threshold of p ≤ 0.05.