Landsat Calibration & Validation
While Landsat satellites are well-designed and calibrated prior to launch, continuous recalibration is required to offset degradation that may be caused by mechanical or electrical effects, or exposure to UV radiation. Calibration requires a comparison between the measuring instrument and an “absolute” reference standard of known accuracy.
Landsat Radiometric Characterization and Calibration
Reflectance, radiance, and atmospheric conditions all affect the digital number (DN) values of Landsat data. Radiometric calibration employs algorithms and processes that improve Landsat data. This is done by converting the DN values of the data to spectral radiance (at the sensor), and then to reflectance (also at the sensor). This is followed by the removal of atmospheric effects, which are due to absorption and scattering, to perform atmospheric correction (reflectance at the surface). The Landsat 8 and Landsat 9 Data Users Handbooks also provide more information on radiometric characterization and calibration.
Calibration Parameter Files
Calibration Parameter Files (CPFs) provide radiometric and geometric coefficients needed for processing of raw, uncorrected Landsat image data. Each timeframe-specific CPF contains calibration coefficients that have been adjusted to correct for the time varying performance of the sensor.
The Calibration Parameter File page allows the searching and downloading of CPFs specific to each Landsat sensor, and displays definition documents and notices about changes that affect the files.
Response Linearization Look Up Tables
Response Linearization Look Up Tables (RLUT) are optional additional files that accompany Landsat 8 and Landsat 9 Calibration Parameter Files (CPF) and contain a mapping look up table to linearize the output of the OLI detectors.
Bias Parameter Files
Bias Parameter Files (BPF) are available for Landsat 8 and Landsat 9. BPFs supply radiometric correction parameters during Level-1 processing of Landsat 8 and Landsat 9 data products.
ECCOE Test Sites Catalog
The ECCOE Test Sites Catalog contains prime candidate worldwide test sites for the calibration and post-launch characterization of space-based optical imaging sensors.
The Catalog also includes pseudo invariant calibration sites (PICS), which are considered benchmarks for on-orbit calibration, since they are essentially invariant over time; are spatially very uniform and have stable spectral response over time; the atmospheric effects on upwelling radiance is minimal due to high surface reflectance; and are in regions where rainfall is limited, preventing vegetative growth and very sparse human populations.
Ref: Absolute Calibration of Optical Satellite Sensors Using Libya 4 Pseudo Invariant Calibration Site, Remote Sensing 2014, 6(2), 1327-1346; doi:10.3390/rs6021327.
Landsat Mission Underfly Opportunities
Throughout the Landsat Program’s long mission history, calibration and characterization of data are of paramount importance. One of the best methods for cross-calibration between instruments is imaging near-coincidentally in tandem using an underfly with an earlier mission sensor. The images below display the result of the Landsat 9 underfly with Landsat 8 over Puerto Vallarta, Mexico on November 11, 2021. The left image shows the Landsat 8 OLI image and the right image is from Landsat 9 OLI. Both images are shown as a true color image using the red, green, and blue bands (Bands 4|3|2).
The underfly activities of Landsat 5 through Landsat 9 are described on the Landsat Mission Underfly Opportunities webpage.
Landsat Geometric Validation
Accurate geometry ensures that Landsat data pixels are aligned, and that the data can be used easily in time series analysis. The exceptional geometric qualities of Landsat 8 and Landsat 9 OLI/TIRS data are used to improve the reference database used to precisely and accurately geolocate all Landsat Level-1 data products. Landsat Science products inherit the geometry of Landsat Level-1 data. Validating the geometric accuracy of Landsat data incorporates the known processing levels, the root-mean-square error (RMSE) information, and the use of Ground Control Points.
The Landsat Geometry webpage provides additional details about the Landsat Ground Control Points, Landsat Levels of Processing, and performance tests that were done on the Landsat 8 instruments.
Ground Control Points (GCPs)
GCPs are points on the surface of the Earth of known location, used to geo-reference Landsat Level-1 imagery. GCPs are updated as needed to continually improve Landsat data. GCPs can be downloaded and used as reference data. Visit the Landsat Ground Control Point webpage to learn more.
Levels of Processing
To assure Landsat Level-1 data are suitable for time-series analysis, products need to be co-registered. The root-mean-square error (RMSE) reported in the metadata (MTL.txt) file can be used to filter the precision and terrain corrected Level-1 data products to meet application specific requirements. Landsat processing levels and their accuracies are listed on the Landsat Levels of Processing webpage.