Reflection of light from semi-infinite absorbing turbid media. Part 2: Plane albedo and reflection function

We study the accuracy of a number of simple approximate equations for the reflection characteristics of semi-infinite light scattering media (e.g., for the diffuse reflectance of a turbid layer under collimated illumination conditions and also for the reflection function). Spectra of diffuse reflection under monodirectional illumination by a wide beam R (xi) or the plane albedo are handled in technological applications using different approximations depending on the level of light absorption in the medium. Generally speaking, the value of R depends not only on the cosine of incidence angle xi and the similarity parameter s = root(1 - omega(o)) (1 -omega(o)g)(-1) (omega(o) is the single scattering albedo, g is the asymmetry parameter), but also on the phase function of a turbid layer. The dependence on the phase function is reduced to the dependence on the asymmetry parameter for the low probability of photon absorption in the medium. We find that the influence of the angular behavior of the phase function cannot be neglected in calculations of the reflection function. Then the best choice is the solution of the nonlinear integral equation for the reflection function. We also show a number of approximate results, which can be used to model the reflection function. The results obtained can be used for the solution of both direct and inverse problems of light scattering media optics. (C) 2006 Wiley Periodicals, Inc.