Spectral reflectance of drying, sandy soils

A high-resolution time series of the spectral reflectance of drying, sandy soils reveals sensitivities to the drying process that appear to be characteristic of the disposition of water on the surface of the soil. The increase in reflectance is clearly related to the decrease in overall water content, but the spectral details of the relationship are dependent on the link between soil and water at the surface (e.g., porosity, size distribution, the presence of adsorbed vs. free water). Spectral characteristics appear to be most consistently sensitive to the changes in the presence and disposition of water when the soil is near saturation and again during the final stages of drying. At those times the reflectance changes are most sensitivity to the proportion of pore water, adsorbed water and exposed particles.