Preflight and In-Flight Calibration of the Spectral Profiler on Board SELENE (Kaguya)

Abstract

The Spectral Profiler (SP) is a visible-near infrared spectrometer on board the Japanese Selenological and Engineering Explorer, which was launched in 2007 and observed the Moon until June 2009. The SP consists of two gratings and three linear-array detectors: VIS (0.5-1.0 μm ), NIR 1 (0.9-1.7 μm), and NIR 2 (1.7-2.6 μm). In this paper, we characterize the radiometric and spectral properties of VIS and NIR 1 using in-flight observational data as well as preflight data derived in laboratory experiments using a calibrated integrating sphere. We also proposed new methods for radiometric calibration, specifically methods for nonlinearity correction, wavelength correction, and the correction of the radiometric calibration coefficients affected by the water vapor. After all the corrections, including the photometric correction, we obtained the reflectance spectra for the lunar surface. Finally, we examined the stability of the SP using the SP data near the Apollo 16 landing site observed at four different times. The difference in reflectance among these four observations was less than ~ ±1% for most of the bands, suggesting that the degradation of the SP is not significant over the mission period.