Review to estimate Evapotranspiration from remote sensing data: some examples from the simplified relationship to the use of m

Different methods have been developed to estimate evapotranspiration from remote sensing data. Among them direct methods based upon the energy balance equation and using thermal infrared (TIR) data like the simplified relationship. This method has been applied for various situations: from small spatial scale using airborne TIR images to continental scale with NOAA data. More recently indirect estimates using assimilation procedures and Soil-Vegetation-Atmosphere Transfer (SVAT) models have been developed. In this last case, the combination of different wavelength domains is often required so as to get input parameters of these models to characterize the different surfaces like albedo, emissivity or Leaf Area Index. A brief review of these different approaches is presented. Some examples are shown on the site of the Alpilles Reseda project, where various types of models (Sebal, Meso-NH...) were used to estimate surface fluxes from remote sensing data. The main physical bases and assumptions of these models are also discussed in this paper.