Diffuse reflectance spectroscopy: a comparison of the theories.

The various theories of diffuse reflectance spectroscopy are compared mathematically, and it is concluded that the modified particle model theory is probably the most nearly correct. If so, the comparison shows that the simple, easily applied simplified particle model theory is approximately valid for relative index of refraction values of 1.5-2.5 and that the Kubelka-Munk remission function is approximately applicable in the traditional sense. Expressions were obtained for the Kubelka-Munk constants in terms of the fundamental optical parameters, and the depth of penetration of radiation into a powdered sample was investigated.