ARCSTONE: Calibration of Lunar Spectral Reflectance from Space ESTO InVEST (Update)

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. This on-orbit radiometric spectral reference helps enable high-accuracy absolute calibrations and inter-calibrations of past, current, and future Earth-observing sensors, meteorological imagers, and long-term climatemonitoring satellite systems. The goal of the ARCSTONE In-Space Validation of Earth Science Technologies (InVEST) project, funded by NASA ESTO, is to demonstrate its novel lunar measurement approach from space and improve the Moon as a radiometric SI-traceable reference for high-accuracy on-orbit calibrations spanning the visible and nearinfrared spectral regions. The ARCSTONE instrument is a compact spectrometer which will be accommodated on a 6U CubeSat intended for low Earth orbit with planned readiness for launch in about 2 years. It will measure the lunar spectral reflectance with combined standard uncertainty of 0.5% (k=1) across the 350 nm to 2300 nm spectral range. The ARCSTONE InVEST team will present the status of the project, the instrument design, calibration approach, concept of operations, and the planned path toward mission implementation