Mapping Surface Broadband Emissivity of the Sahara Desert Using ASTER and MODIS Data

Surface broadband emissivity in the thermal infrared region is an important parameter for the studies of the surface energy balance. This paper focuses on estimating a broadband window emissivity from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Moderate Resolution Imaging Spectrometer (MODIS) data. Both sensors are on board the NASA Earth Observing System (EOS) Terra satellite, which was launched in 1999. First, several definitions of the broadband emissivity were investigated, and it was found that the emissivity integrated between 8 and 13.5 lm is the best for estimating the net longwave radiation under clear-sky conditions. Then, a method to estimate broadband emissivity at the continental scale was developed. The method uses two regressions. The first regression is to relate the broadband emissivity to the emissivities for the five ASTER channels using measured emissivities in the laboratory from spectral libraries. The second regression relates the broadband emissivity map from ASTER data to * Corresponding author address: Kenta Ogawa, Hitachi Ltd., 4-6 Kanda-Surugadai ChiyodaKu, Tokyo 101-8010, Japan. E-mail address: [email protected] Earth Interactions Volume 8 (2004) Paper No. 7 Page 1