A new look at the simplified method for remote sensing of daily evapotranspiration

A modification of the so-called “Simplified Method” used to obtain the integrated daily evapotranspiration from surface radiant temperature over variable vegetation cover is proposed. Mathematically, the simplified equation takes the form Rn24−LE24=(To13−Ta13)n, where Rn24 and LE24 are, respectively, the integrated net radiation and evapotranspiration over a 24-h period and T013 and Ta13 are, respectively, the surface radiant and the 50-m air temperatures at 1300 local time. B and n are pseudo constants given as functions of the normalized difference vegetation index (NDVI), expressed as a scaled index N*. Both N* and Ta13 are obtained with the aid of remotely determined measurements, which are viewed on scatterplots of T013 versus NDVI.