Retroreflection is a property of a surface such that incident radiation is reflected directly back in the incident direction. Most bright diffusely reflecting surfaces have a retroreflectance strength up to twice that of off normal viewing; this is true for low coherence as well as laser illumination. The effect is known to occur for the lunar surface. However, for dark surfaces, the retroreflectance can be of an order of magnitude greater than off normal. The cause of retroreflectance is related to the scattering properties of a surface. For bright diffuse surfaces, and reduce the polarization of the surface. At large incident angles multiple scattering is less which results in a high polarization. The phenomenon is of great importance for laser target designator and missile guidance, particularly for low reflectance targets, thereby increasing their vulnerability. Thus it is a fallacy to paint or coat targets black to reduce their vulnerability to polarized laser radiation. Recent experiments on the retroreflectance of various surfaces show polarization, wavelength, and surface structure dependence. Also implicit in the causes of the phenomenon is the optical complex index of refraction of the surface material constituents. Data will be presented on the retroreflectance properties of surfaces, and the relation to the polarization of the incident radiation.
Walter G. Egan,
"Dark-target retroreflection increase", Proc. SPIE 3754, Polarization: Measurement, Analysis, and Remote Sensing II, (25 October 1999); doi: 10.1117/12.366331; https://doi.org/10.1117/12.366331