A NEW LOOK AT THE SIMPLIFIED METHOD FOR REMOTE-SENSING OF DAILY EVAPOTRANSPIRATION

A modification of the so-called ''Simplified Method'' used to obtain t he integrated daily evapotranspiration from surface radiant temperatur e over variable vegetation cover is proposed. Mathematically, the simp lified equation takes the form Rn-24 - LE(24) = B(T-013 - T-a13)(n), w here Rn-24 and LE(24) are, respectively, the integrated net radiation and evapotranspiration over a 24-h period and T-013 and Ta-13 are, res pectively, the surface radiant and the 50-m air temperatures at 1300 l ocal time. B and n are pseudo constants given as functions of the norm alized difference vegetation index (NDVI), expressed as a scaled index N. Both N* and T-a13 are obtained with the aid of remotely determine d measurements, which are viewed on scatterplots of T-013 versus NDVI.