Submitted to: European Geophysical Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: February 24, 2003
Publication Date: April 6, 2003
Citation: Schmugge, T.J., Ogawa, K., Jacob, F., French, A.N., Ritchie, J.C. 2003. Determination of the window emissivity with ASTER multi-spectral thermal infrared data [abstract]. European Geophysical Society Meeting. Geophysical Research Abstracts, 5:01594.
Knowledge of the land surface window (8 - 12 micrometer) emissivity is important for estimating the longwave radiation budget. With the successful launch of NASA's Terra satellite in December 1999 a new tool for observing land surface emissivity became available, i.e. multi-spectral 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 and spatial variations of surface emissivity when used with the Temperature Emissivity Separation (TES) algorithm to extract the temperature and 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. To validate the approach we will present results from ASTER data acquired over the Jornada Experimental Range and the White Sands National Monument in New Mexico during 2000, 2001 and 2002. 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. 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 channel little spatial variation of the emissivity was observed with values of 0.96 +/- 0.005 over large areas. Emissivity values from the ASTER data for the gypsum at White Sands were in good agreement with values calculated from the lab spectra for gypsum and with each other. Maps of ASTER emissivities extracted from data acquired in 2001 and 2002 over a 240 x 1200 km area for a desert region of North Africa, including the sand dunes of the Grand Erg Oriental are presented. The spectra for the sand dunes showed good agreement with that expected for quartz sand based on laboratory measurements. A multiple regression approach was used to relate the emissivities of the 5 ASTER channels to the window channel emissivity. The results were compared with a classification based emissivity map and significant differences were found, ranging between -0.08 and +0.06. These results show that ASTER data can be used to map the spatial and spectral variations of surface over large areas in particular the deserts of the world for which there is much exposed soil and sand.