Landsat Collection 2 Level-2 Science Products: Surface Reflectance and Temperature

The U.S. Geological Survey (USGS) produces research-quality, application-ready Level-2 Science Products from Landsat Collection 2 Level-1 data. They are used to monitor, assess and project changes in land use, land cover and environmental conditions that affect people, natural processes and habitats.

The products are time series of observations, processed for consistency and continuity so that they can measure the effects of environmental change. They also serve as input to Landsat's Level-3 Science Products for essential climate variables.

Studying how the land surface has changed over time depends on radiometric data that are consistent and processed to the highest scientific standards. Following guidelines of the World Meteorological Organization's Global Climate Observing System, the USGS set out to produce higher-level Landsat products for research on climate variability and change.

Landsat 5 images of Zhuozhou, China, on 7 September 1999: top-of-atmosphere (TOA) reflectance, Level-2 surface reflectance (SR), and Level-2 surface temperature (ST) in kelvin. Credit: U.S. Geological Survey.

Surface reflectance

Landsat Collection 2 surface reflectance (SR) measures the fraction of incoming sunlight reflected from Earth's surface to the Landsat sensor, with the effects of the atmosphere removed or reduced. It approximates what a sensor at nadir would record once the atmosphere has been compensated for.

Removing atmospheric effects makes images of the surface more consistent and easier to compare. Many higher-level remote sensing products depend on SR, including:

• vegetation indexes;
• albedo;
• leaf area index;
• burned area;
• land cover and land cover change.

Landsat 8 SR data are made with the Land Surface Reflectance Code (LaSRC); Landsat 4–7 SR data with the Landsat Ecosystem Disturbance Adaptive Processing System (LEDAPS) algorithm.

Surface temperature

Landsat Collection 2 surface temperature (ST) measures the temperature of Earth's surface in kelvin, with atmospheric effects removed or reduced. Surface temperature from remote sensing is an important geophysical parameter in studies of the global energy balance and in hydrologic modelling. Landsat ST products help monitor:

• crop and vegetation health;
• extreme heat events, including natural disasters such as volcanic eruptions and wildfires;
• urban heat islands.

The product uses a single-channel algorithm across the Landsat sensors that measure emitted thermal infrared radiation. It is generated from the Collection 2 Level-1 thermal infrared bands, with these inputs:

• top-of-atmosphere (TOA) reflectance and TOA brightness temperature (BT);
• emissivity from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Emissivity Database, and ASTER Normalized Difference Vegetation Index (NDVI) data;
• atmospheric profiles of geopotential height, specific humidity and air temperature — from the Goddard Earth Observing System Model Version 5 Forward Processing Instrument Teams (GEOS-5 FP-IT) for acquisitions from 2000 on, and from the Modern Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) for 1982 to 1999.

For Landsat 7 Enhanced Thematic Mapper Plus (ETM+) products, the Band 6 TOA, BT and ST data come from ETM+ Band 6 high (6H) and Band 6 low (6L) merged together. The merged band holds the unsaturated pixels from Band 6H; where a Band 6H pixel's brightness temperature falls outside the band's dynamic range (240 to 322 kelvin), the Band 6L pixel is used instead. Pixels saturated in Band 6L stay saturated in the merged band, which is then used to make the TOA BT and ST data.

Getting the data

Collection 2 SR and ST products are available worldwide as scenes, and for the United States as Landsat Analysis Ready Data (ARD) tiles, from the USGS Earth Resources Observation and Science (EROS) Center through EarthExplorer (https://earthexplorer.usgs.gov; on the "Data Sets" tab, "Landsat — Landsat Collection 2 Level-2" or "Landsat C2 Analysis Ready Data (ARD)").

Level-1 data are processed into SR and ST when the solar zenith angle is under 76 degrees and the required auxiliary inputs are available, for these sensors and periods:

"Present" is as of the fact sheet's publication in November 2021.

Sources

• U.S. Geological Survey, 2021, Landsat Collection 2 Level-2 Science Products: U.S. Geological Survey Fact Sheet 2021–3055. https://doi.org/10.3133/fs20213055
• The figure is taken from the fact sheet's PDF.
• Rewritten in hubnx's own words.