Using Remote sensing technique for estimation of real evapotranspiration

Evapotranspiration is not easy to measure; Specific devices and accurate measurements are required to determine evapotranspiration. In this research, using the RS technique, the amount of real evapotranspiration will be determined in Chaviz sub-basin of Ilam dam catchment. n this study, there has been employed the image of ETM+ Landsat satellite dated June the 15th 2010. ENVI4.7 software was used to obtain the needed information from the image of ETM+ Landsat satellite. The daily information for estimation of evapotranspiration of reference crop was provided from Ilam weather forecast station. Finally, geometric calculations were done using ArcGIS9.3 software and there were obtained outputs from the prepared maps. In this work, real evapotranspiration has been estimated using bands 3&4 of ETM+ satellite and also vegetation fraction index. This is a new method for evaluating real evapotranspiration in the catchment and regional scale. The results show that real evapotranspiration with values of the 0-2.92 mm/day is dominant in Chaviz sub-basin. The most largest area in which evapotranspiration happens is the area of ranges (%63). Forest land use in the next rank. The maximum evapotranspiration happens in gardens (8.9 to 11.71 mm/day) but they cover only a little area of the basin (%10) and the minimum evapotranspiration happens in the land use of the ranges (0 to 2.92 mm/day) which covers a large area of the basin (%63). Base on the results of this study, it can be claimed that the rate of evapotranspiration is low in Chaviz sub basin (Ilam dam). Also, since this range of evapotranspiration coincides the area of ranges, it can be said that land use of the ranges enjoys less evapotranspiration comparing with other kinds of land uses and its water needs are accordingly lower than others.

Remote sensing, Real evapotranspiration, ETM+ satellite, Ilam dam.