Spectral reflectance time series of four soils while drying from over-saturated to air-dry

Changes in the spectral reflectance of drying soil are slow and rather subtle for much of the drying time, becoming more rapid and dramatic only when readily available pore water has been depleted. Tracking changes in reflectance at frequent intervals as soil dries, and considering the observations as a time series, can provide insight into the relationship between spectral changes and the underlying soil moisture status. This paper describes time series of laboratory measurements of the spectral reflectance of four distinct soils collected at 15-min intervals as the soils progress from oversaturated to air-dry. Continuous changes in reflectance as water evaporates over time are described, and a spectral Fresnel component to the reflectance of oversaturated soil is documented. A rationale for a metric to detect the end of constant evaporation is presented, along with an approach for identifying and distinguishing among bare soils in satellite or aircraft imagery. The observations also provide insight into the challenges of designing spectral metrics intended to gather useful information regarding moisture content and soil characterization. • Spectral reflectance time series of four soils from oversaturated to air-dry. • A spectral metric is associated with the end of the constant evaporation period. • Evidence of Fresnel reflectance from oversaturated soil in the VNIR only. • Normalized difference pairs for differentiating among soils with remote sensing.