FIRMS: What are MODIS and VIIRS collections?

[Earthdata - wxedward]

What are MODIS and VIIRS collections?

Reprocessing of the entire MODIS and VIIRS data archive is periodically performed to incorporate better calibration, algorithm refinements, and improved upstream products into all MODIS or VIIRS products. The updated data archive resulting from each reprocessing is referred to as a collection. Later collections supersede all earlier collections.

For Terra MODIS, Collection 1 consists of the first products generated following launch. Terra MODIS data were reprocessed for the first time in June 2001 to produce Collection 3. Note that this first reprocessing was numbered Collection 3, rather than Collection 2, as one would expect. Collection 3 was also the first produced for the Aqua MODIS products. Collection 4 reprocessing was initiated in December 2002 for Terra MODIS and somewhat later for the Aqua MODIS. Collection 5 began reprocessing in early 2007. Improvements in Collection 5 included adding the Fire Radiative Power value to the fire detections and refining the detection confidence to more accurately identify questionable active fire pixels. Collection 6 reprocessing began in 2015. In terms of fire detections, the key differences between Collection 5 and Collection 6 were that: Collection 6 extends processing to oceans and other large bodies, including detection of off-shore gas flaring; there was a reduction in false alarms in the Amazon caused by small forest clearings. Collection 6.1 has been available since April 2021 and is the latest collection available. In terms of fire detections, there are no algorithm changes; the update is from changes and enhancements to the calibration approach used in the generation of the Terra and Aqua MODIS Level 1B products. For further details on C61 calibration changes and other changes, the user is encouraged to refer to the pdf summarizing Collection 6.1 specific changes.

For the most up to date information, see the MODIS Collection 6/6.1 Active Fire Product User's Guide (updated May 2021)