Retroreflectance measurements of photometric standards and coatings. Part 2.

Measurements of the opposition effect (brightening in the retroreflectance direction) have been extended to geometries with the normal of reflecting surface tilted up to 60 degrees from the incident direction. Surface tilt appears to have little or no effect on the retroreflecting properties of MgCO(3), BaSO(4) paint, colloidal sulfur, or white Nextel paint for 0.6328-microm laser or 0.6-microm low coherence illumination. Source collimation-sensor acceptance angle decrease from 1 degrees with 0.6328-microm laser illumination increases the opposition effect. The theoretical explanation of the effects observed may lie in the use of the Mie theory for highly collimated incident radiation.