Orbital and surface photography collected during the Apollo 16 mission can be used to calibrate existing Earth-based, high-resolution radar maps of the lunar surface. The absence of any theoretical treatment of the radar backscatter from irregular rocks has prevented the assignment of radar-echo cross sections to specific size distributions of rocks. This gap will now be filled with the use of ground truth provided by metric and panoramic camera photographs and by surface photographic data collected by the astronauts.