ARCSTONE: Calibration of Lunar Spectral Reflectance from Space

Detecting and improving the scientific understanding of global trends in complex Earth systems, such as climate, increasingly depend on assimilating datasets from multiple instruments and platforms over decadal timescales. Calibration accuracy, stability, and inter-consistency among different instruments are key to developing reliable composite data records from sensors in low Earth and geostationary orbits, however, achieving sufficiently low uncertainties for these performance metrics poses a significant challenge. Space-borne instruments commonly carry on-board references for calibration at various wavelengths, but these increase mass and mission complexity and are subject to degradation in the space environment. The Moon can be considered a natural solar diffuser which can be utilized as an on-orbit calibration target by most space-borne Earth-observing instruments. Since the lunar surface reflectance is effectively time-invariant, establishing the Moon as a high-accuracy calibration reference enables broad inter-calibration opportunities even between temporally non-overlapping instruments and provides an exo-atmospheric absolute radiometric standard. The ARCSTONE mission goal is to establish the Moon as a reliable reference for high-accuracy on-orbit calibration spanning the visible and near-infrared spectral regions. The ARCSTONE instrument is a compact spectrometer which will be packaged on a 6U CubeSat intended for low Earth orbit. It will measure the lunar spectral reflectance with accuracy \u3c 0.5% (k=1), sufficient to establish an SI-traceable absolute lunar calibration standard referenced to the spectral solar irradiance across the 350 to 2300 nm spectral range. This lunar reference will help to enable high-accuracy absolute calibrations and inter-calibrations of past, current, and future Earth-observing sensors, meteorological imagers, and long-term climate monitoring satellite systems. The ARCSTONE team will present the development status of the instrument, results from laboratory characterizations and functional tests, and the planned path toward mission implementation