Influence of Sand-Grain Morphology and Iron-Oxide Distribution Patterns on the Visible and Near-Infrared Reflectance of Sand-Textured Soils

The overall shape of a sand grain can be defined by two morphological properties, namely sphericity and roundness, and it is largely determined by soil-formation and weathering processes. In this paper, we investigate the effects of these properties on the visible and near-infrared reflectance of sand-textured soils characterized by the presence of iron oxides. Our investigation is supported by computer simulations performed using the SPLITS (Spectral Light Transport Model for Sand) model and considering actual sand characterization data. Our findings indicate that the influence of grain morphology may vary considerably depending on the distribution patterns of iron oxides present in sand-textured soils. These minerals may occur as pure particles, as contaminants mixed with the grain parent material, or as coatings. Since these distribution patterns are also significantly affected by soil-formation and weathering processes, we believe that the combined influence of sand-grain shape and iron-oxide distribution patterns on the reflectance of sandy landscapes should be carefully taken into account in the retrieval of information about their mineralogy and environmental history.