Determination of optical parameters for light penetration in particulate materials and soils with diffuse reflectance (DR) spectroscopy

The results of our investigations of particulate materials (aluminium oxide, quartz sand) and "real world" soils (a brown sand and a dark brown soil) using diffuse reflectance (DR) spectroscopy are presented. The findings are discussed within the framework of Kubelka-Munk (KM) theory as a simplified description of light propagation in highly turbid media. The relation between the KM and the Lambert-Beer (LB) treatment is outlined. The KM parameters determined were the scattering and absorption coefficients (S and K, respectively), and the light penetration depths, dp(KM). It was found that in the UV/VIS spectral range the scattering coefficients of the materials investigated vary by ca. one order of magnitude (S = 6-> 100 cm-1), whereas the absorption coefficients change by more than three orders of magnitude (K = < 1-> 1500 cm-1). The different absorption and scattering properties of the materials lead to strong variations in light penetration depths from the micron into the mm regime [dp(KM) = < 20-> 3500 microns].