Eleven years of ASTER onboard calibration

The ASTER is a high-resolution optical sensor for observing the Earth on the Terra satellite launched in December1999. The ASTER consists of three radiometers. The VNIR has three bands in the visible and near-infrared region, the SWIR has six bands in the shortwave infrared region, and the TIR has five bands in the thermal infrared region. The onboard calibration devices of the VNIR and SWIR were halogen lamps and photodiode monitors. In orbit three bands of the VNIR showed a rapid decrease in the output signal. The band 1, the shortest wavelength, decreased most to 70% in eleven years. The VNIR spectra of the responsivity degradation were compared to other sensors, the JERS-1 OPS, the OCTS, the Hyperion, the MODIS, the MISR and the SPOT. The temperature of the onboard blackbody of the TIR is varied from 270 K to 340 K in the long term calibration for the offset and gain calibration. The long term calibration of the TIR showed a decrease in response after launch. The decrease was most remarkable at band 12 decreasing to 60% in eleven years. The degradation spectra of the TIR shows that the possible causes of the degradation might be silicone and hydrazine.