L2 AERDT (Aerosol Dark Target) Product Description
The L2 Continuity Aerosol Dark Target product is a Level-2 product generated at 6x6 km (VIIRS, at nadir) spatial resolution. The L2 Continuity Aerosol Dark Target data product file always has a prefix of AERDT_L2 and contains data collected from the SNPP/VIIRS platform.
Aerosol & Atmosphere Products
Aerosol products are a subset of a larger group of atmosphere products. In addition to the aerosol products there are separate atmosphere products such as cloud and water vapor products. The product file names provide information about the product type, content and resolution. The naming conventions for the aerosol products are described in the next section.
Atmosphere products, including the aerosol products, are archived and can be obtained at the LAADS DAAC and also at the EARTHDATA portal. Either site can be used to search for and download data. Note that the two sites are not identical and have different search and visualization capabilities. MODIS product files are stored in HDF format. VIIRS product files are in NETCDF format. A downloadable tutorial for LAADS DAAC site and several other remote sensing resources is available on the NASA ARSET website. Another easy way to visually search and find files for an individual event is to use the NASA Worldview site. Worldview has an online tutorial. VIIRS products are not yet available on Worldview
In addition to the information available in this guide the MODIS-atmos product pages provide an excellent overview as well as in-depth information on not only the MODIS aerosol product but also the water vapor, cloud, cloud mask and aerosol profile products. New and intermediate users of MODIS atmosphere data would do well to familiarize themselves with this content available there as well as bookmark it for reference. MODIS-atmos has recently added a section on “continuity products”. These are products developed initially for MODIS but updated around a common core to allow porting to VIIRS and other instruments. The DT VIIRS product is one of the continuity products.
NASA satellite product developers are constantly working to evaluate, update and improve their products. From time to time after significant changes are made to the algorithm and/or instrument calibration the entire data set for a single or related group of instrument products will be reprocessed using the new algorithm and/or calibration. The set of data products created using the same set of algorithms and calibration coefficients is referred to as a collection. MODIS Collection 6 (C6) was released in 2016 for all atmosphere products. A smaller update was later applied and, as of this writing the current MODIS collection is Collection 6.1 (C6.1). Generally, only the most recent data set is available to the public for use. If older data collections are required one should inquire with the NASA LAADS DAAC.
VIIRS products are still in their initial release and are referred to as collection 1. When searching for VIIRS level 2 data at LAADS DAAC, after selecting the VIIRS:Suomi-NPP product, under collection users will need to select 5110 – NPP_L1_C1_V2_Processing.