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 Rn-24 - LE(24) = B(T-013 - T-a13)(n), where 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, 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 T-a13 are obtained with the aid of remotely determined measurements, which are viewed on scatterplots of T-013 versus NDVI.