干旱区生态环境知识资源中心

The multispectral thermal infrared data obtained from the Advanced Spaceborne Thermal Emission and Reflection (ASTER) radiometer have been shown to be of good quality. ASTER is on NASA's Terra satellite. It has 5 bands in the 8 to 12 micrometer waveband with 90 to spatial resolution, when the data are combined with the Temperature Emissivity Separation (TES) algorithm the surface emissivity over this wavelength region can be determined. This paper will present some quantitative emissivity results obtained over test sites in southern New Mexico, USA; the Jornada Experimental Range and the White Sands National Monument which are compared with ground measurements. The Jornada site is typical of a desert grassland where the main vegetation components are grass and shrubs with a large fraction of exposed soil. While the White Sands site is mainly dunes of gypsum sand which provides relatively good homogenous emissivity target. More than a dozen ASTER scenes over these New Mexico test sites have been acquired since the launch of Terra in December 1999. There were simultaneous field campaigns in May of 2000, 2001 and 2002 and September/October 2001 and 2002. Also, simultaneous MASTER (MODIS-ASTER airborne simulator) coverage was obtained for several of the dates. In spite of the 90 m resolution, the results appear to be in good quantitative agreement with laboratory measurements of the emissivity for the quartz rich soils of the Jornada with values < 0.85 for the 8 - 9 micrometer channels. For the longest wavelength channels little spatial variation of the emissivity was observed with values of 0.96 +/- 0.005 over large areas. Emissivity values derived from several ASTER scenes for the gypsum at White Sands were in good agreement with field measurements and values calculated from the lab spectra for gypsum and with each other. Gypsum has a strong emissivity minimum centered on the ASTER 8.63 micrometer band, and the satellite results for this band agree within 0.01 of the value calculated from the laboratory spectra.