Abstract
Calibration accuracy, long-term precision, and inter-consistency are key on-orbit performance metrics for Earth observing sensors. The accuracy and consistency of environmental measurements across multiple instruments in low Earth and geostationary orbits are directly connected to the scientific understanding of complex systems, such as Earth’s weather and climate. Recent studies have demonstrated the quantitative impacts of observational accuracy on the quality of science data products and the ability to detect climate change trends for essential climate variables (e.g., Earth’s radiation budget, cloud feedback, and long-term trends in cloud parameters). It is common for instruments to carry on-board references for calibration at various wavelengths, but these can be subject to degradation, and also increase mass and risk.
The Moon can be considered a natural solar diffuser in space. Establishing the Moon as a high-accuracy calibration reference enables broad inter-calibration opportunities, as the lunar reflectance is effectively time-invariant and can be directly measured by most Earth-observing instruments. Existing approaches to calibrate sensors against the Moon can achieve stabilities of tenths of a percent over a decade, as demonstrated by the SeaWIFS. However, current lunar calibration capabilities have uncertainties of 5 – 10%, attributed to the photometric model of the Moon. Significant improvements in the lunar reference and calibration are possible, and are necessary for improving accuracy of Earth climate observations.
The ARCSTONE mission goal is to provide a reliable reference for high-accuracy on-orbit calibration for reflected solar instruments. The ARCSTONE instrument is a lunar/solar spectrometer intended to fly on a CubeSat in low Earth orbit. It will provide lunar spectral reflectance with accuracy < 0.5% (k = 1), sufficient to establish an SI-traceable absolute lunar calibration standard for past, current, and future Earth environmental, weather and climate sensors. The ARCSTONE team will present the instrument design status and path forward for development, building, calibration and testing.
ARCSTONE: Calibration of Lunar Spectral Reflectance
Calibration accuracy, long-term precision, and inter-consistency are key on-orbit performance metrics for Earth observing sensors. The accuracy and consistency of environmental measurements across multiple instruments in low Earth and geostationary orbits are directly connected to the scientific understanding of complex systems, such as Earth’s weather and climate. Recent studies have demonstrated the quantitative impacts of observational accuracy on the quality of science data products and the ability to detect climate change trends for essential climate variables (e.g., Earth’s radiation budget, cloud feedback, and long-term trends in cloud parameters). It is common for instruments to carry on-board references for calibration at various wavelengths, but these can be subject to degradation, and also increase mass and risk.
The Moon can be considered a natural solar diffuser in space. Establishing the Moon as a high-accuracy calibration reference enables broad inter-calibration opportunities, as the lunar reflectance is effectively time-invariant and can be directly measured by most Earth-observing instruments. Existing approaches to calibrate sensors against the Moon can achieve stabilities of tenths of a percent over a decade, as demonstrated by the SeaWIFS. However, current lunar calibration capabilities have uncertainties of 5 – 10%, attributed to the photometric model of the Moon. Significant improvements in the lunar reference and calibration are possible, and are necessary for improving accuracy of Earth climate observations.
The ARCSTONE mission goal is to provide a reliable reference for high-accuracy on-orbit calibration for reflected solar instruments. The ARCSTONE instrument is a lunar/solar spectrometer intended to fly on a CubeSat in low Earth orbit. It will provide lunar spectral reflectance with accuracy < 0.5% (k = 1), sufficient to establish an SI-traceable absolute lunar calibration standard for past, current, and future Earth environmental, weather and climate sensors. The ARCSTONE team will present the instrument design status and path forward for development, building, calibration and testing.