ASTER/TIR onboard calibration status and user-based recalibration

Abstract

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), one of five sensors on Terra, has five bands (10 to 14) in the thermal infrared (TIR) region. These TIR bands are radiometrically calibrated by one onboard blackbody with the function of changing temperature between 270 and 340 K. In normal operation the blackbody is set up at 270 K, and a constant coefficient in a quadratic radiometric calibration equation for each detector is adjusted at that temperature before each Earth observation, but the gain coefficient cannot be adjusted at this time, while it can periodically be updated by long term calibration in which the blackbody is measured at 270, 300, 320, and 340 K. On the other hand the sensor response of all bands (particularly band 12) has been degrading since the launch, and periodical updating of the gain coefficient does not fully follow the degradation, so that the calibration error on level-1 (L1) products is often unacceptable. We therefore have developed a recalibration method which is easily applied to L1 products by a general user. By using this method, the calibration error will mostly be reduced below the level of NEDT.

Temperature and emissivity separation from ASTER data for low spectral contrast surfaces

“…science.aster.ersdac.or.jp/RECAL), and depend on the date of the scene acquisition and the Radiometric Calibration Coefficient (RCC) version applied to the scene. The re-calibration is aimed to correct for the temporal decline of the detectors responsivity between consecutive changes in the RCC version (Tonooka et al, 2003) and it is necessary for ASTER TIR products with RCC versions 1.x and 2.x (2.17, 2.18 and 2.20, respectively, for our three scenes). Recent changes in the processing make the re-calibration unnecessary for RCC versions 3.x and higher.…”

“…Then, the scene-based re-calibration procedure of Tonooka et al (2003) was applied to the above L s,j in order to obtain the ASTER at-sensor calibrated radiances, L s,j (c). The re-calibration is linear; i.e.…”

ASTER TIR Radiometric Calibration and Atmospheric Correction

“…Table 6.1 shows the odd-detector average, the even-detector average, and the total average of sensor response reduction between the first LTC day (March 12, 2000) and November 7, 2005, where the sensor response is defined as the reciprocal of C 1 . As shown, the degradation rate is dependent on an odd/even difference of the detector number (Tonooka et al 2003). The sensor response reduction reaches 28% in band 12 as of November 7, 2005, while it is about 10% in band 10, and further, it is 1-2% larger in even detectors (Nos.…”

“…All the ASTER TIR bands are reportedly degrading since the instrument's launch, and the ten detectors in each band show a common trend (Sakuma et al 2002(Sakuma et al , 2005Tonooka et al 2003. Figure 6.2 shows the average of gain coefficients C 1 over ten detectors for each band as a function of the number of days since launch (December 18, 1999).…”

“…Table 6.2 gives the LTC date and its day number since launch for each of RCC version 2.x. As shown, the database was not always updated in a timely manner because of the delays in the analysis and validation of the coefficients derived from the LTC, which often causes calibration errors (Tonooka et al 2003). In particular, the RCCs for database versions 2.05 and 2.06, applied to products observed from user-based recalibration method for level-1 products was developed (Tonooka et al 2003).…”