Trend Analysis of Onboard Calibration Data of Terra/ASTER/VNIR and One of the Suspected Causes of Sensitivity Degradation

Sensitivity degradation trend is analyzed for ASTER: Advanced Spaceborne Thermal Emission and Reflection radiometer/Visible and Near-Infrared Radiometer: VNIR onboard Terra satellite. Fault Tree Analysis is made for sensitivity degradation. Firstly, it is confirmed that the VNIR detectors are stable enough through dark current and shot noise behavior analysis. Then it is also confirmed that radiance of calibration lamp equipped VNIR is stable enough through lamp monitor of photodiode output data analysis. It is confirmed that radiance at the front of VNIR optics is, on the other hand, degraded in conjunction with sensitivity degradation of VNIR through an analysis of another photodiode output data which is equipped at the front of VNIR optics, photodiode output is scale-off at around one year after the launch though. VNIR optics transparency might not be so degraded due to the fact that VNIR output and the later photodiode output show almost same degradations. Consequently, it may say that one of possible causes of VNIR sensitivit