Landsat Collections: How the USGS Sorts Its Satellite Archive by Quality

U.S. Geological Survey Fact Sheet 2018–3049, August 2018.

In 2016 the USGS reorganised the Landsat archive into a tiered collection. The structure gives every Landsat Level-1 product a known, consistent quality — so images can be compared over time and "stacked" — while the archive keeps improving and new data stay available as soon as they arrive. It is a major change in how the archive is managed, keeping quality consistent through time and across instruments.

Landsat Collection 1 holds all Level-1 data since 1972 from:

• Landsat 8 Operational Land Imager (OLI) / Thermal Infrared Sensor (TIRS);
• Landsat 7 Enhanced Thematic Mapper Plus (ETM+);
• Landsat 4–5 Thematic Mapper (TM);
• Landsat 1–5 Multispectral Scanner (MSS).

The three tiers

Landsat 8 and 7 data reach the Real-Time tier within about 12 hours; after final calibration they are reprocessed into Tier 1 (RMSE up to 12 m) or Tier 2 (more than 12 m). Images by NASA.

Why tiers? To:

• keep a consistent archive of known quality;
• provide data within 12 hours for the International Charter on disasters, to help limit harm to lives and property;
• offer the highest-quality inventory and processing of Landsat Level-1 products ever made;
• support pixel-by-pixel time-series analysis and data stacking.

Reading a product name

Each Collection 1 product's identifier shows which tier it belongs to:

LXSS_LLLL_PPPRRR_YYYYMMDD_yyyymmdd_CC_TX

Examples from the fact sheet: LC08_L1GT_029030_20151209_20160131_01_RT, LE07_L1TP_016039_20040918_20160211_01_T1, LT04_L1GS_017036_19821115_20160315_01_T2 and LM01_L1GS_017039_19760131_20160225_01_T2.

Other Collection 1 changes

Every Collection 1 Level-1 product also comes with:

• new Quality Assessment (QA) bands and angle coefficient files;
• extra metadata fields: saturation bits and a land cloud cover assessment;
• a new cloud algorithm, CFMask (C Function of Mask);
• for Landsat 8, the TIRS stray light correction;
• for Landsat 4–5 TM, scenes that lack Payload Correction Data (PCD);
• Calibration Parameter File names that include the collection number, tying each file to its collection;
• renamed Response Linearization Look Up Tables (Landsat 8), which accompany the calibration files.

Getting the data

Collection 1 data are free from EarthExplorer (https://earthexplorer.usgs.gov/), GloVis (https://glovis.usgs.gov/) and the LandsatLook Viewer (https://landsatlook.usgs.gov/). Questions go to Landsat User Services at the USGS Earth Resources Observation and Science (EROS) Center in Sioux Falls, South Dakota (custserv@usgs.gov).

Sources

• U.S. Geological Survey, 2018, Landsat Collections: U.S. Geological Survey Fact Sheet 2018–3049. https://doi.org/10.3133/fs20183049 · https://pubs.usgs.gov/publication/fs20183049
• The tier diagram and the table of product identifiers come from the fact sheet's PDF. Its text gives about 16 days for Landsat 8's final calibration, its diagram about 14–16 days.
• The fact sheet's item for Landsat 4–5 reads "no- Correction Data (PCD) scenes"; PCD is Payload Correction Data.
• Rewritten in hubnx's own words.