Improving the ROLO Lunar Calibration Reference with New Measurements of the Moon

Abstract

The Moon provides a calibration target that can serve as a common reference for all space-based Earth observing sensors. Lunar calibration has the potential to achieve very high accuracy, leading to important capabilities for Earth remote sensing such as inter-calibration of instruments in satellite constellations and building climate data records. Practical use of the Moon for radiometric calibration requires a model to account for the continuously changing lunar brightness and that can accommodate the various viewing geometries of sensors’ Moon observations. The USGS ROLO lunar calibration system operates with a model for the disk-integrated irradiance at reflected solar wavelengths, developed from an extensive set of ground-based observations. Although the ROLO model is widely used, to reach the full accuracy potential of lunar calibration requires collecting new characterization measurements of the Moon to apply toward refining and ultimately reformulating the analytic model that provides the lunar reference. The airborne Lunar Spectral Irradiance (air-LUSI) project is a currently operational system to acquire spectrally resolved measurements of the Moon from the NASA ER-2 high-altitude aircraft, flying above ~95% of the atmosphere.