Emissivity Determination for Land Surface Temperature estimation of Iran using AVHRR Thermal Infrared Data

Foroogh Beik and M. Reza Saradjian
Remote Sensing Division, Surveying and Geomatics Engineering Department,
Faculty of Engineering, University of Tehran, Tehran, Iran


Abstract
Land surface temperature (LST) is one of the key parameters in physics of land-surface processes on regional and global scales. Therefore, precise LST is required for a variety of researches including climatic, hydrological, ecological and biogeochemical studies. The main purpose of this paper is to produce LST map of Iran.

The great difference in land cover and type and accordingly presence of different emissivity values makes the LST algorithm or model development complicated. In order to determine surface type and determine relevant emissivity value for each land cover, a combination of different complementary approaches have been applied. For vegetation cover areas, using AVHRR data, a vegetation map has been constructed from ndvi values first and then emissivity values are calculated for pixels located in areas having ndvi values greater than 0.2 and smaller than 0.7. In order to determine emissivity values for non-vegetated areas, geological maps have been used and five types of land surface have been identified. For other land cover types that were not possible to be identified using ndvi and geological maps, land cover classification was performed on AVHRR data. Therefore, emissivity values of around 40% of land have been determined dynamically from ndvi map and classification map. In order to determine the model coefficients, meteorological data at known coordinates in desert regions at the time of satellite overpass have been used. The results have been analyzed using ground truth data provided at known coordinate, however the model coefficients for the whole country are at final calibration stage.