Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 4, 2000
Publication Date: N/A
Interpretive Summary: 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: Knowledge of the surface emissivity is important for determining the radiation balance at the land surface. For heavily vegetated surfaces, there is little problem since the emissivity is relatively uniform and close to one. For arid lands with sparse vegetation, the problem is more difficult because the emissivity of the exposed soils and rocks is highly variable. With multispectral thermal infrared (TIR) observations, it is possible estimate the spectral emissivity variation for these surfaces. The data we will present is from the Thermal Infrared Multispectral Scanner (TIMS) instrument which has six channels in the 8 to 12 micron region. TIMS is a prototype of the TIR portion of the Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) instrument on NASA's Terra (EOS- AM1) platform launched in December 1999. The Temperature Emissivity Separation algorithm, developed for use with ASTER data, is used to extract the temperature and six emissivities from the six channels of TIMS data. The algorithm makes use of the empirical relation between the range of observed emissivities and their minimum value. This approach was applied to the TIMS data acquired over the USDA/ARS Jornada Experimental Range in New Mexico. The Jornada site is typical of a desert grassland where the main vegetation components are grass (black grama) and shrubs (primarily mesquite) in the degraded grassland. The data presented here are from flights at a range of altitudes from 800m to 5000m yielding a pixel resolution from 3 to 12 meters. The resulting spectral emissivities are in qualitative agreement with laboratory measurements of the emissivity for the quartz rich soils of the site. The derived surface temperatures are in reasonable agreement with ground measurements.