SOIL REFLECTANCE AS A TOOL FOR ASSESSING PHYSICAL CRUST ARRANGEMENT OF FOUR TYPICAL SOILS IN ISRAEL

Abstract

Investigation of soil structural crust reflectance across the NIR-SWIR spectral region was conducted to account for the possibility of remotely sensed soil crust-related properties such as water infiltration. The raindrop energy disintegrates the soil aggregates and rearranges soil particles within the structural crust of the upper soil layer. The generation of structural crust affects the physical properties of the soil and can be identified by significant color changes on the soil’s surface. Spectral differences observed on the crusted soil are caused by the rearrangement of texture and clay minerals during raindrop events. In this study, four soils were subjected to increasing levels of raindrop energy in a rain simulator device with their reflectances measured concurrently. Two wavelengths representing particle size arrangement and clay content at 1.7 μm and 2.2 μm, respectively, were used to generate a dynamic chart of the crust formation. Soil mineralogy was found to be a major factor in the crust formation. In the clayey soils, two identical stages were identified: decreased albedo at 1.7 μm and an increase in the 2.2 μm absorption features. By employing this technique, a washing out of clay from the crust zone over the high raindrop energy was observed. However, in sandy soil, the predominant quartz particles created a different pattern. Because the coarse quartz particles reflect more energy, reverse reciprocal relationships with clay enrichment were found. Based on the relationship between raindrop energy and water infiltration rate (IR), a spectral model for predicting the IR was constructed. Three spectral domains were examined: reflectance (R), the first derivative of the reflectance (R’), and the ratio between reflectance of a given treatment and the reflectance of the non-crusted fog treated soil (R/R_fog). A significant relationship was discovered between the IR and the reflectance properties (R’ and ratio), suggesting clay content as the significant indicator of crust status. The results of this study show that soil reflectance can shed light on the structural crusting process. It is further suggested that this methodology may be used as well at high signal to noise ratios, employing airborne and space-borne hyperspectral sensors.