Effects of granulometric and mineralogical composition on spectral reflectance of soils in a Sahelian area

Abstract

During the Hapex-Sahel international investigation, portable radiometers (Barringer and Cimel) were used to study, in the optical domain, the relationship between soil mineralogical and granulometric compositions and radiometric indices: redness index, colour index and texture index. The results show that the granulometric distribution and the mineralogical composition have both important influence on these indices. In this Sahelian area, for soils having more than 1% of hematite, the redness index presents a high correlation with hematite content. For soils with less than 1% of hematite, the redness index depends on the size of the particles and their distribution at the surface. For eolian sandy and ferricrust soils, the colour and texture indices present good correlations, respectively, with iron oxide and kaolinite content. No such correlation is observed for ferruginous soils because of the complex interactions existing between iron oxides, kaolinite and the size of particles.