Discrimination of Senescent Vegetation Using Thermal Emissivity Contrast

A remote sensing method utilizing multiband thermal infrared (8–12 μm) imagery that discriminates between senescent vegetation and bare soil is described. This discrimination is achieved by computing thermal band emissivities from a temperature-emissivity separation algorithm, and then classifying surface features based on spectral emissivity contrast. In a study of rangelands and winter wheat fields in central Oklahoma, the contrast, or range, of these spectral emissivities is diagnostic of the presence or absence of surface vegetative cover. A large range of emissivities, approximately greater than 0.03, is indicative of bare soil, while a low range, less than 0.02, is indicative of vegetative cover. When knowledge of the emissivity range is combined with a vegetation index, such as NDVI, the surface may be classified by a ternary system: bare soil, green vegetation, and senescent vegetation. Discrimination between bare soil and soil covered with senescent vegetation using emissivity contrast should be feasible in other settings. The benefit of this technique is that heat flux predictions can be based on a more accurate surface representation than otherwise provided by visible and near-infrared land classification schemes.