Abstract
The ASTER Instrument is one of the five sensors on the NASA’s Terra satellite on orbit since December 1999. ASTER consists of three radiometers, VNIR, SWIR and TIR whose spatial resolutions are 15 m, 30 m and 90 m, respectively. Unfortunately SWIR stopped taking pictures since May 2008 due to the offset rise caused by the cooler temperature rise, but VNIR and TIR are taking Earth pictures of good quality. TIR has five bands whose center wavelengths are 8.3 mm, 8.6 mm, 9.1 mm, 10.6 mm and 11.1 mm. TIR experienced responsivity degradation. Band 12 (9.1 mm) decreased 40 % and most among five TIR bands. Some vicarious calibration activities support these trends. The decrease fit well with the exponential decrease. There are some discussions of the causes of the responsivity degradation of TIR. Possible causes are contamination accretion by silicone outgas, thruster plume and plasma interaction. Hydrazine has the absorption spectra corresponding to the TIR responsivity degradation in the infrared region. We studied the IAM effect on the ASTER by allocating the additional onboard calibration activity just before and after the IAM while the normal onboard calibration activity is operated once in 49 days. As another possibility we marked silicone outgas. Some siloxanes in silicone outgas have the absorption maxima near 9 mm. We studied spectral similarity between siloxane absorbance and TIR responsivity degradation.
Onboard Calibration Trends of ASTER/TIR
The ASTER Instrument is one of the five sensors on the NASA’s Terra satellite on orbit since December 1999. ASTER consists of three radiometers, VNIR, SWIR and TIR whose spatial resolutions are 15 m, 30 m and 90 m, respectively. Unfortunately SWIR stopped taking pictures since May 2008 due to the offset rise caused by the cooler temperature rise, but VNIR and TIR are taking Earth pictures of good quality. TIR has five bands whose center wavelengths are 8.3 mm, 8.6 mm, 9.1 mm, 10.6 mm and 11.1 mm. TIR experienced responsivity degradation. Band 12 (9.1 mm) decreased 40 % and most among five TIR bands. Some vicarious calibration activities support these trends. The decrease fit well with the exponential decrease. There are some discussions of the causes of the responsivity degradation of TIR. Possible causes are contamination accretion by silicone outgas, thruster plume and plasma interaction. Hydrazine has the absorption spectra corresponding to the TIR responsivity degradation in the infrared region. We studied the IAM effect on the ASTER by allocating the additional onboard calibration activity just before and after the IAM while the normal onboard calibration activity is operated once in 49 days. As another possibility we marked silicone outgas. Some siloxanes in silicone outgas have the absorption maxima near 9 mm. We studied spectral similarity between siloxane absorbance and TIR responsivity degradation.