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Title: QUANTITATIVE ESTIMATES OF EMISSIVITY USING ASTER DATA

Author
item Schmugge, Thomas
item JACOB, FREDERIC - PRIVATE CONSULTANT
item FRENCH, ANDREW - NASA/GSFC
item OGAWA, KENTA - HITACHI LTD

Submitted to: International Symposium on Recent Advances in Quantitative Remote Sensing
Publication Type: Proceedings
Publication Acceptance Date: 11/21/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: With the successful launch of the Terra satellite in December 1999 a new tool for observing land surface properties became available, i.e. multispectral thermal infrared data from the Advanced Spaceborne Thermal Emission and Reflection (ASTER) radiometer. ASTER has 5 channels in the 8 to 12 micrometer wave band with 90 meter resolution. 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. This is significant for arid lands with sparse vegetation because the emissivity of the exposed soils and rocks is highly variable. The results we will present are from ASTER data acquired over the Jornada Experimental Range in New Mexico during 2000 and 2001, a total of 9 scenes. 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. The Temperature Emissivity Separation (TES) algorithm is used to extract the temperature and 5 emissivities from the 5 channels of ASTER data. TES makes use of an empirical relation between the range of observed emissivities and their minimum value. In spite of the 90 m resolution, the results appear to be in quantitative agreement with laboratory measurements of the emissivity for the quartz rich soils of the site with values < 0.85 for the 8 - 9 micrometer channels. For the longest wavelength channel little spatial variation of the emissivity was observed with values of 0.96 ± 0.005 over large areas. The White Sands National Monument with its dunes of gypsum sand was also within several of the scenes. Emissivity values from May, 2000 through May , 2002 scenes for the gypsum at White Sands were in good agreement with values calculated from the lab spectra for gypsum and with each other. The results for vegetated targets show little or no spectral variation with emissivities > 0.97. Ground TIR brightness temperature measurements were made in 7 x 7 grids with 5 m spacing using broadband radiometers at several sites. The resulting average temperatures were in good agreement with those derived from the ASTER data.