MODIS Dark Target Aerosol Products Overview
MODIS dark target aerosol products are available in 10 km and 3 km resolution in separate files. The products are further separated and identified as either Terra (MOD04) or Aqua (MYD04) MODIS products. New product versions are released periodically as the algorithms which create the products are updated. Each product version is referred to as a Collection. All MODIS atmosphere products for Aqua and Terra were re released for Collection 6 in 2015. Aqua and Terra products from the prior release, Collections 5 and 5.1, are still available.
MODIS geophysical products (as opposed to raw data) from a single overpass of the satellite sensor are referred to as Level 2 products. The Level 2 products are made available in files of five minute segments of the satellite overpass called granules. Both the Terra and Aqua satellites have a 16 day orbital cycle. Granules with the same time designation which are 16 days apart will be in the same geographic location. Global composites from multiple satellite overpasses are Level 3 products. The information on this website will pertain principally to the MODIS dark target algorithm and Level 2 dark-target aerosol products. Information on dark target algorithm modifications and products for other platforms can be found in the "Platforms" section of this website.
The designation as a 10 km or 3 km aerosol product refers to the resolution of the product (not the sensor!) at the center of the satellite swath. These products include retrieval parameters over land and ocean. The 10 km product will include data from the Deep Blue retrieval algorithm and a merged dark target-deep blue product. For more information on the merged product please see our FAQ. The 10 km product files are designated as MOD04_L2 or MYD04_L2. The full naming convention is explained below. The 3 km product contains only dark target (not deep blue) retrievals over both land and ocean. These files are designated MOD04_3Km or MYD04_3Km. Files for both products are stored in HDF format which includes both data and metadata.
Although land and ocean data parameters (referred to as Scientific Data Sets or SDS) exist side by side in all MODIS aerosol products, the algorithms used to create land and ocean products are completely separate. Therefore whenever possible we present information about the products in distinct land and ocean sections although they will be found in the same file.
MODIS 10 km Aerosol HDF file names have the following naming convention:
Terra file: MOD04_L2.AYYYYDDD.HHMM.CCC.YEARDAYHRMNSC.hdf
Aqua file: MYD04_L2.AYYYYDDD.HHMM.CCC.YEARDAYHRMNSC.hdf
YYYY, DDD and HHMM are four digit year, three digit Julian day, and time of day in UTC, CCC is the collection (005 for Collection 5, 051 for Collection 5.1 and 006 for Collection 6), and YEARDAYHRMNSC represents when the file was processed.
Sample name for a collection 6 Terra aerosol file from day 79 of 2002 at 0255 UTC.
The MOD04 and MYD04 files include many parameters, each stored as a Scientific Data Set (SDS) within the file.
The ocean, land and 3 km product sections of the website will give more details about the products and their most frequently used parameters (SDS).
Where to obtain Modis aerosol products:
Modis aerosol products can be obtained from the LAADS Web - http://ladsweb.nascom.nasa.gov. Files can be searched in a variety of ways or can be directly downloaded from their ftp site.