It is important to estimate land surface evapotranspiration (ET) for water resources evaluation, drought monitoring and crop production simulation. The most important information needs to irrigation performance, is the evapotranspiration (ET) of the plants, especially field crops. Knowing about the crop was the necessity for calculating anything about it. When facing a water basin of very large area, agro-climatically transient in its various parts, treating the ET calculation by the energy-balance becomes interesting. Information about the vegetation cover is indeed minimal and often very well provided by satellite information. Some various satellites are used, Landsat7 ETM+, NOAA AVHRR, TERRA MODIS and TERRA ASTER. Only satellites able to provide temperature measurements are fulfilling the requirements of such analysis. Some meteorological satellites are also used for calculating ET in Global Climatologically Models, but are of too low spatial resolution for the application to crop ET per selected farm. Validations of such monitoring algorithms have been widely performed and are always found acceptable. It is concluded that SEBAL model is useful to calculate ET by means of remote sensing measurements and other meteorological data.
