Estimate Actual Evapotranspiration by SEBS Algorithm and Comparison with Actual Measured Values by Scintillometer

The purpose of this study was to evaluate the accuracy of SEBS remote sensing algorithm to determine the actual evapotranspiration of an alfalfa field located in Isfahan province. An automatic weather station was installed in the alfalfa field to measure and to record the required weather data for the calculation of reference evapotranspiration by the Penman-Monteith equation. Daily and hourly grass reference evapotranspiration (ETr) were calculated by FAO Penman-Monteith equation (FAO56), using the meteorological data measured during the satellite passing time. The FAO 56 crop coefficient was used to obtain alfalfa evapotranspiration from ETr. The actual hourly alfalfa evapotranspiration (ETc-h) from an extensive alfalfa field surface at the time of the passage of the LANDSAT 8 from the study area was computed by SEBS algorithm and at the same time it was measured by a Scintillometer and they were found to be 0.7 and 0.65 (mm/hr), respectively. The actual ET obtained by SEBS usually overestimated values measured by the Scintillometer (LAS). The actual hourly and daily alfalfa evapotranspiration values obtained from SEBS algorithms were compared with the corresponding values measured by the Scintillometer (LAS) and values calculated by the FAO Penman-Monteith equation and R2 of 0.75( p<0.01) ,0.86( p<0.01) and RMSE 0.04 (mm/hr) , 0.43 (mm/day) were obtained , respectively.