The knowledge of evapotranspiration is of great interest in many applications such as assessing irrigation water use. In this paper, a methodology is presented to estimate evapotranspiration using the surface energy balance model S-SEBI (Simplified Surface Energy Balance Index) and the evaporative fraction. The method is applicable under the assumptions of constant atmospheric conditions and sufficient wet and dry pixels over the image. The model uses remotely sensed parameters such as albedo, MSAVI (Modified Soil Adjusted Vegetation Index) and surface temperature and emissivity images. The methodology has been applied over the Barrax test site, located in the province of Albacete (Castilla La Mancha, Spain), in the framework of the DAISEX (Digital Airborne Imaging Spectrometer Experiment) campaigns carried out by ESA (European Space Agency). Net radiation, soil heat fluxes and evapotranspiration have been obtained from DAIS images for alfalfa, corn and grass plots. The results show that alfalfa plot gives the highest values, around 5 mm dK1, whereas corn plot gives the lowest, around 3.5 mm dK1. The proposed methodology leading to an accuracy for the daily evapotranspiration lower than 1 mm dK1.