In 2016, the USGS started reorganizing the Landsat archive into a formal tiered data Collection structure. This data Collection structure ensures that Landsat Level-1 products provide a consistent archive of known data quality to support time series analyses and data “stacking”, while controlling continuous improvement of the archive and access to all data as they are acquired.
Starting with Collection 1, every Landsat 1-5 Multispectral Scanner (MSS), Landsat 4-5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM+), and Landsat 8 Operational Land Imager (OLI) / Thermal Infrared Sensor (TIRS) scene is assigned to a specific tier. Data in Tier 1 meet formal geometric and radiometric quality criteria. Tier 2 do not meet the Tier 1 criteria. The Real-Time Tier contains data immediately after acquisitions that use estimated parameters. Real-Time data are reprocessed and assessed for inclusion into Tier 1 or Tier 2 as soon as final parameters are available.
The implementation of Collections represents a significant change in the management of the Landsat Archive by ensuring consistent quality through time and across instruments, along with additional changes like metadata and file names.
The Landsat Collections Web page contains the details about all aspects of the Landsat Collection 1 effort.