The resolution of an imaging system can be quantified using the modulation transfer function (MTF) derived from an image with an edge feature. For Earth-viewing satellites, imaging an appropriate terrestrial edge feature is difficult when optical blur from the atmosphere contaminates the MTF. With a sharp edge and no atmosphere, our Moon has provided researchers with an alternative by deriving the line spread function from the lunar edge. The Moon’s surface, however, has features, e.g., craters and seas, that depart from clean step-like behavior, making curve fitting to the data difficult and diminishing the effectiveness of the method. We demonstrate an improvement in which a reflectance (albedo) map of the Moon, created from a mosaic of the U.S. Department of Defense/NASA Clementine images, is used to flatten the surface features before the edge spread function is measured. The objective is to improve the reliability of MTF measurements for on-orbit calibration of the National Oceanic and Atmospheric Administration/NASA Geostationary Operational Environmental Satellite (GOES) weather satellites and similar missions. The technique is applied to the reflective bands of the Advanced Baseline Imager on GOES-16 and GOES-17 weather monitoring satellites.