4 May 2006 Reflectance of some water-wetted sands
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Abstract
Water is a common, transient soil material that can be distributed as lattice water bound in crystalline particles, as water of adhesion on the soil particles, and as interstitial or capillary water. It can have important effects on soil reflectance spectra over the visible-near infrared-short wave infrared electromagnetic spectrum, 0.4-2.5 μm. This study's objective was to determine the changes in soil reflectance spectra relative to differences in soil water content. An initial small water application greatly reduced the soil reflectance, masked the spectral features of the air-dry soils, and enhanced water absorption features. As wavelength values increased, water absorptance increased and transmittance decreased, which created non-uniform change in the soil reflectance spectrum. These changes occurred as water filled the interstitial spaces within the soil's optical depth. Water filling the pore space below the sample's optical depth increased the substrate's moisture content but had no effect on substrate reflectance. These water absorption features were amplified over the 0.4-2.5 μm region and spectral sensitivities to water increased directly with wavelength. Soil reflectance maxima in five spectral bands, centered at 0.800, 1.080, 1.265, 1.695, and 2.220 μm, varied inversely with sample water content. The 0.800 and 1.080 μm bands varied more slowly with water content than did the 1.265, 1.695, and 2.220 μm bands. Multiple normalized difference indices (NDI) using these bands correlated strongly with sample water content.
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Melvin B. Satterwhite, C. Scott Allen, "Reflectance of some water-wetted sands", Proc. SPIE 6233, Algorithms and Technologies for Multispectral, Hyperspectral, and Ultraspectral Imagery XII, 62331L (4 May 2006); doi: 10.1117/12.665574; https://doi.org/10.1117/12.665574
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