Abstract
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), which is a multiband pushbroom sensor suite onboard Terra, has successfully provided valuable multiband images for approximately 20 years since Terra’s launch in 1999. Since the launch, sensitivity degradations in ASTER’s visible and near infrared (VNIR) and thermal infrared (TIR) bands have been monitored and corrected with various calibration methods. However, a unignorable discrepancy between different calibration methods has been confirmed for the VNIR bands that should be assessed with another reliable calibration method. In April 2003 and August 2017, ASTER observed the Moon (and deepspace) for conducting a radiometric calibration (called as lunar calibration), which can measure the temporal variation in the sensor sensitivity of the VNIR bands enough accurately (better than 1%). From the lunar calibration, 3–6% sensitivity degradations were confirmed in the VNIR bands from 2003 to 2017. Since the measured degradations from the other methods showed different trends from the lunar calibration, the lunar calibration suggests a further improvement is needed for the VNIR calibration. Sensitivity degradations in the TIR bands were also confirmed by monitoring the variation in the number of saturated pixels, which were qualitatively consistent with the onboard and vicarious calibrations.
Highlights
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), which is a multiband-sensor suite composed of visible and near infrared (VNIR), shortwave infrared (SWIR), and thermal infrared (TIR) sensors onboard Terra [1], has successfully operated for 20 years since Terra’s launch in 1999, and ASTER has provided numerous multiband images for those 20 years [2]
Characteristics of the radiometric performance of ASTER have been continuously monitored with several calibration methods, such as onboard calibration [3], vicarious calibration [4,5,6] and cross calibration [7,8], and sensitivity degradations in the VNIR, SWIR, and TIR have been confirmed
Since the measurement of the sensitivity degradations is used for correcting the observed brightness in ASTER products as radiometric correction coefficients (RCC), the accurate measurement for the degradation is important to maintain the reliability of the ASTER products
Summary
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), which is a multiband-sensor suite composed of visible and near infrared (VNIR), shortwave infrared (SWIR), and thermal infrared (TIR) sensors onboard Terra [1], has successfully operated for 20 years since Terra’s launch in 1999, and ASTER has provided numerous multiband images for those 20 years [2]. In addition to VNIR calibration, the Moon can be used to confirm the sensitivity degradation of the TIR bands by monitoring variation in the number of saturated pixels in a TIR image when the TIR sensor observes the Moon. On the other hand, based on the degradation trend in the TIR bands [6], it is expected that the TIR sensor captured images of the Moon with a much smaller number of saturated pixels in 2017 if the TIR observes the Moon with a lunar surface temperature profile similar to that in 2003. Each lunar calibration result will be used to assess validity of the results from other calibration approaches
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