Absolute diffuse reflectance from relative reflectance measurements.

A method is presented whereby any photometer than can measure relative diffuse reflectance of materials in the laboratory can be used to measure absolute diffuse reflectance of such samples without any modification to the apparatus. No additional integrating spheres or special optical geometries are required. All that is needed are two powdered materials, one a very strong absorber and one a very weak absorber at the wavelength of interest, a requirement that is not difficult to meet. A theoretical development based on the Kubelka-Munk theory, the results of experimental testing, and an error analysis are presented.