NBS reference retroreflectometer

A long-range retroreflectance instrument has been built in the photometric range of the Radiometric Physics Division of the NBS. It is designed to measure photometric properties of retroreflectors for different geometries. It satisfies many needs of the measurement community, and it is planned to use this instrument as the basis for a Measurement Assurance Program (MAP) and for Standard Reference Materials (SRM). This paper describes the design and testing of the instrument. Some estimated uncertainties for typical samples are given.