Landsat-7 ETM+ Radiometric Calibration Status.

Area of Science:

• Earth Observation
• Remote Sensing
• Radiometric Calibration

Background:

• The Landsat-7 satellite, launched in 1999, carries the Enhanced Thematic Mapper+ (ETM+) instrument, which has been operational for 17 years.
• Continuous monitoring of the ETM+ on-orbit radiometric performance is crucial for maintaining the integrity of the long-term Landsat data archive.
• Radiometric calibration of reflective bands relies on both on-board calibration devices and Pseudo-Invariant Calibration Sites (PICS).

Purpose of the Study:

• To report on the on-orbit radiometric performance characterization of the Enhanced Thematic Mapper+ (ETM+) instrument on the Landsat-7 satellite.
• To validate recent calibration updates and assess the long-term radiometric stability of the ETM+ sensor.
• To evaluate the effectiveness of Pseudo-Invariant Calibration Sites (PICS) in monitoring sensor degradation.

Main Methods:

• Radiometric calibration gains for reflective bands were updated in April 2013, primarily using Pseudo-Invariant Calibration Sites (PICS) data.
• A comparison with the SADE database of PICS results was conducted to assess additional degradation post-update.
• Thermal band calibration was updated in October 2013, incorporating efforts from NASA/Jet Propulsion Lab and Rochester Institute of Technology.

Main Results:

• The April 2013 calibration update corrected for sensor degradation, with worst-case bands showing changes as high as -0.2% per year.
• New comparisons with PICS data indicate no further degradation in the updated calibration, suggesting stability.
• The thermal band calibration update addressed a bias error of 0.31 W/m² sr, resulting in a stable lifetime trend within +/- 0.4K.

Conclusions:

• The Enhanced Thematic Mapper+ (ETM+) on Landsat-7 demonstrates stable radiometric performance following recent calibration updates.
• Pseudo-Invariant Calibration Sites (PICS) remain an effective tool for monitoring sensor calibration, although recent trends require further investigation.
• The updated calibration ensures the continued reliability of Landsat-7 data for long-term Earth observation applications.