Reflection and backscattering

Dahm and Dahm [62,63] have developed a discontinuum theoretical treatment based on the original work of Benford [67]. It is assumed that each layer of material is bounded by two parallel infinite planes. Of the radiation entering the fth layer, the total forward flux, that is, the fraction leaving the layer in the same direction, is U, and the total backward flux is n, and the fraction absorbed is at. The total forward flux includes both transmission and forward scatter and the total backward flux includes both external and internal reflection and backscatter. 

In total, the layer will remit a certain fraction, which represents the sum of reflection and backscatter absorb a certain fraction and transmit (either directly or diffusely) the balance. 

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