LAUSR

We assessed the degradation of the radiance lamp in the onboard calibration system of the Spectral Profiler, a hyperspectral sensor onboard the Japanese Selenological and Engineering Explorer (SELENE), which was launched in September 2007 and observed the Moon until June 2009. We found that the output of the radiance lamp soon after launch increased by 3.2%–4.6% as compared with the prelaunch output, after which it decreased over time. The total decrease during the mission lifetime of about 1.5 years after the increase of 3.2%–4.6% was ~1.1%–1.5%, which is slightly larger than the < 1% degradation of the sensitivity of the sensor, as derived from vicarious calibration using the Apollo 16 landing site observations. Thus, we confirmed that the radiance lamp became degraded, but the degree of degradation was within 1% during ~1.5 years. We also found a wavelength dependence in the degradation, in which degradation was larger for shorter wavelengths, especially for wavelengths less than ~ $0.8\,\mu \text{m}$ . The trend of the wavelength dependence was shown to be consistent with a model of blackbody radiance with a decrease in temperature of the lamp of about −5 K, suggesting that the degradation of the lamp was mostly due to temperature decrease of about −3 K/yr. Our results may provide an important constraint on the quantitative assessment of the degradation of the sensitivity of remote-sensing sensors using an onboard calibration system, such as the Advanced Spaceborne Thermal Emission and Reflection Radiometer.