Schmugge, T (schmugge@hydrolab.arsusda.gov) , USDA/ARS Hydrology and Remote Sensing Lab, Bldg. 007 - BARC West, Beltsville, MD 20705 United States
Ogawa, K (k-ogawa@dsg.hitachi.co.jp) , Hitachi Ltd., 4-6 Kanda-Surugadai Chiyoda- Ku,, Tokyo, 101-8010 Japan
Ogawa, K (k-ogawa@dsg.hitachi.co.jp) , Faculty of Engineering,University of Tokyo, University of Tokyo, Tokyo, 113-0033 Japan
Rokugawa, S (rokugawa@gpl.t.u-tokyo.ac.jp) , Faculty of Engineering,University of Tokyo, University of Tokyo, Tokyo, 113-0033 Japan
Abstract
Knowledge of the land surface emissivity is important for estimating the longwave radiation budget, a decrease of soil emissivity by 0.1 will increase ground and air temperature by about 1.1 C and 0.8C and decrease net and upward longwave radiation by about 6.6 and 8.1 W/m*m, respectively. The multi-spectral thermal infrared data from the Advanced Spaceborne Thermal Emission and Reflection (ASTER) radiometer provides a new tool for observing land surface emissivity . 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. TES makes use of an empirical relation between the range of observed emissivities and their minimum value to extract the temperature and 5 emissivities from the 5 channels of ASTER data. The approach was validated with ASTER data acquired over the Jornada Experimental Range and the White Sands National Monument in New Mexico between 2001 and 2003 yielding good agreement with ground measures of emissivity. The approach was extended to produce maps of emissivities over a 400 x 1200 km area for a desert region of North Africa, including the sand dunes of the Grand Erg Oriental using data acquired in 2001 and 2002. The spectra for the sand dunes showed good agreement with that expected for quartz sand based on laboratory and field 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. The spatial variation of the emissivity observed by ASTER is from 0.8 to 1, which corresponds to a range of 15 w/m*m in the net surface longwave radiation under a dry atmosphere. These results show that ASTER data can be used to map the spatial and spectral variations of surface emissivity over large areas in particular the deserts of the world for which there is much exposed soil and sand. To extend the map to continental scales a relationship between (a) the ASTER broadband emissivity map and (b) spectral emissivity and spectral reflectance data from MODIS data was developed. We applied this regression to MODIS data and generated a broadband emissivity map for North Africa. The range of the broadband emissivity was found to be between 0.86 and 0.96 for the desert area. The expected RMS error of the map is about 0.02. Such an emissivity map has been used as an input to a climate model and improves the prediction of surface and air temperatures by up to 1 degree C.
Link to abstract on the American Geophysical Union's website: Determination of the Infrared Emissivity with Multi-spectral Thermal Infrared Data from Space
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