The use of multispectral TIR data for observing the spectral emissivity of arid lands

With the successful launch of the Terra satellite a new tool for observing land surface properties becomes available, i.e. multispectral thermal infrared data from the the Advanced Spaceborne Thermal Emission Reflectance Radiometer (ASTER) instrument. These data can be used to assess the spectral variations of surface emissivity. Knowledge of the surface emissivity is important for determining the radiation balance at the land surface. For arid lands with sparse vegetation the problem is difficult because the emissivity of the exposed soils and rocks is highly variable. The data the authors present are from the airborne TIMS instrument which has multiple channels in the 8 to 12 μm region from flights over the Jornada Experimental Range in New Mexico. The Jornada site is typical of a desert grassland where the main vegetation components are grass and shrubs. The Temperature Emissivity Separation (TES) algorithm is used to extract the temperature and 6 emissivities from the 6 channels of TIMS data. TES makes use of an empirical relation between the range of observed emissivities and their minimum value. Data were obtained at 2 and 4 meter resolutions during the summer of 1997 and the results are in quantitative agreement with laboratory measurements of the emissivity for the quartz rich soils of the site with values <0.8 for the 8-9 μm channels. For the longest wavelength channel little spatial variation of the emissivity was observed with values of 0.96±0.005 over large areas