Fractional retroreflection and observation angularity measurements using imaging technology

Abstract

NIST has developed a photometric imaging based method for the measurement of the coefficient of retroreflected luminance. The imaging technology based system simultaneously collects a complete dataset of coefficients of retroreflected luminance (−4° < α < 4°, −π < ρ < π) for a given entrance angle and orientation angle. The advantages include the time required to collect a large number of data points. Over a million data points can be collected in one minute compared to the collection of a thousand data points, which are an incomplete sampling of the retroreflected rho angle and observation angle space, in over 3 hours. The fast measurement of the large number of points allows for a smaller uncertainty for the determination of parameters such as fractional retroreflectance and observation angularity. The direct comparison of the two methods revealed that a larger point-by-point set is required to validate the imaging method.

Keywords:

• fractional retroreflection
• imaging photometer
• observation angularity
• retroreflection
• uncertainty

Acknowledgement

The author would like to thank Yuqin Zong, Chris Gaudette, and Dennis Couzin for their invaluable help and discussions.