Gonioreflectometer for measuring spectral diffuse reflectance

Gonioreflectometric determination of reflectance factors that involves hemispherical collection of reflected flux, which is an alternative to integrating sphere-based methods, is discussed. A detailed description of a gonioreflectometer built at the Helsinki University of Technology is presented. The instrument is used to establish an absolute scale of total diffuse reflectance factors throughout the spectral range 360-830 am. The hemispherical reflectance factors are obtained through integration of the gonioreflectometric measurement results. The reflectance factors of white high-quality artifacts can be determined with a combined standard uncertainty of 0.20%. Results of test measurements were found to be in agreement with values traceable to other absolute scales based on integrating-sphere methods. (C) 2004 Optical Society of America.