ABSTRACT
Retroreflectance by a rough surface is the brightness increase of a surface as the sourcesurface-observer angle (also termed the phase angle in astronomy) is decreased. Peaking is independent of the orientation of the surface relative to the source or observer. Retroreflectance (the opposition effect) was first discovered by Barabashev [1], who observed a sharp rise in the reflective intensity of lunar maria when the moon is full. This was further confirmed by Markov [2], van Diggelen [3], and Gehrels et al. [4].
