There is currently no single theoretical treatment of diffuse reflectance data that is definitive and applicable to all cases. Continuous and discontinuous mathematical approaches have each been developed, and each has merits and limitations. Discontinuous approaches usually incorporate the feature of modeling a sample as a series of distinct layers, parallel to each other and perpendicular to the incident beam. The Representative Layer Theory has been proposed as a mechanism for modeling a particulate sample as a series of layers, enabling one to use the discontinuous mathematics. This paper outlines the Representative Layer Theory, compares and contrasts it with other theories of diffuse reflectance and presents examples that illustrate the strengths and weaknesses of the various theories.
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