Addressing Needs to Achieve High-accuracy Lunar Calibration

Established techniques that use the reflected light from the Moon for sensor radiometric calibration typically utilize the spatially integrated quantity of lunar spectral irradiance. The USGS ROLO model (and its replicated variants) has seen widespread use as the reference for lunar calibration since its development in the early 2000s. Although absolute scale uncertainties persist in the current ROLO model version, a predictive model for lunar spectral irradiance potentially can achieve tenths-percent uncertainty or better, with SI traceability. This would enable a number of important capabilities for on-orbit calibration of Earth observing sensors. To advance development toward a high-accuracy lunar calibration reference requires obtaining new characterization measurements of the Moon that have verified uncertainties and traceability to primary radiometric standards. But to reach the levels of accuracy potentially achievable for lunar calibration also requires increased attention to and improvement in techniques for deriving irradiance measurements from Moon observations acquired by imaging sensors. For example, properly evaluating the oversampling of the Moon disk can present a considerable challenge for line-scanning imagers. The Operational Land Imager (OLI) on Landsats 8 and 9 provides a superb test bed for developing techniques for high-precision measurements of lunar irradiance from line-scanned Moon images. Both OLI instruments observe the Moon monthly at about 7 degrees phase angle, scanning the disk with all 14 Focal Plane Modules over two orbits. The 30-meter ground resolution produces Moon images with disk diameters of about 250 pixels, and the scans oversample the Moon by factors of about 8. The lunar disk can be framed using line-of-sight analysis derived from the Landsat ancillary data feed. This paper will discuss how newly available, high-accuracy lunar irradiance measurements can inform the absolute scale for redeveloping the lunar calibration reference, and will overview the advanced techniques being developed for processing the line-scanned images of the Moon acquired by OLI