A VIIRS Dark Target Operational Product to Continue the MODIS Aerosol Record

A continuous long-term satellite data record for aerosol optical depth (AOD) is possible if the same retrieval algorithm can be adapted for new sensors before the original instruments reach the end of their operational lifespan. Aerosol measurements from MODIS Terra and Aqua are expected to continue only until the early 2020s, covering a little over two decades. However, the VIIRS data record begins in 2012 for Suomi-NPP and in 2018 for NOAA-20, and future launches are planned. A version of the Dark Target (DT) AOD retrieval originally developed for MODIS is now available as an operational product for VIIRS SNPP. In general, the difference between Dark Target AOD for VIIRS SNPP and MODIS Aqua is smaller than the difference between MODIS Aqua and MODIS Terra, and VIIRS DT shows good agreement with AOD retrievals from AERONET. The offset between MODIS and VIIRS versions of the algorithm has several causes, including calibration and sampling. These are investigated along with the spatial and temporal variability of the VIIRS-MODIS offset. The VIIRS SNPP product is also compared to Dark Target retrievals adapted to NOAA-20 and geostationary imagers.