Submitted to: International Geoscience and Remote Sensing Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: June 1, 2000
Publication Date: July 24, 2000
Interpretive Summary: With the launch of NASA's Terra satellite in December 1999, a new tool for studying the earth's surface has become available, multispectral thermal infrared. These data can be used to estimate the emissivity of the land surface on a global basis. The emissivity of the surface has a major effect on the radiation energy balance at the earth's surface. Therefore, knowledge of the spatial variation of the surface emissivity is important for quantifying the radiation balance at the earth's surface. This paper presents preliminary results of a technique for observing this spatial variation. While these results were obtained using data from an aircraft sensor, it is extendable to data from satellite platforms and thus could be used on a global basis.
Technical Abstract: 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 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 we will present are from flights over the Jornada Experimental Range in New Mexico with the TIMS instrument, which has six channels in the 8 to 12 micrometer region. 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 micrometer channels. For the longest wavelength channel, little spatial variation of the emissivity was observed with values of 0.96 plus or minus 0.005 over large areas.