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Question:

How accurate is the radiometric calibration of Landsat images?

Answer:

Continuous monitoring of radiometric stability and instrument performance ensures consistent radiometric response of Landsat data through time and prevents introduction of long-term artifacts.

The USGS characterizes radiometric performance of the Landsat sensors with respect to absolute radiometric accuracy, relative gains of detectors, SNR, detection, characterization, and correction of artifacts, as well as a variety of additional measures.

Calibration updates, due to changes in sensor responsivity, are incorporated when necessary to ensure that user applications derived from the data, especially those multi-temporal applications that use data from multiple sensors, are not impacted by calibration errors. 

Section 3 of the Landsat Collection 1 Level-1 Product Definition document provides more details about the radiometric calibration of Landsat Collection 1 Level-1 scenes.