EFFECTS OF GRANULOMETRIC AND MINERALOGICAL COMPOSITION ON SPECTRAL REFLECTANCE OF SOILS IN A SAHELIAN AREA

During the Hapex-Sahel international investigation, portable radiomete rs (Barringer and Cimel) were used to study, in the optical domain, th e relationship between soil mineralogical and granulometric compositio ns and radiometric indices: redness index, colour index and texture in dex. The results show that the granulometric distribution and the mine ralogical 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 s oils with less than 1% of hematite, the redness index depends on the s ize of the particles and their distribution at the surface. For eolian sandy and ferricrust soils, the colour and texture indices present go od correlations, respectively, with iron oxide and kaolinite content. No such correlation is observed for ferruginous soils because of the c omplex interactions existing between iron oxides, kaolinite and the si ze of particles.