Evaluation of Remote Sensing Technology in Estimation of Evapotranspiration of Alfalfa Using Evapotranspiration Data Estimated by Lysimeter in Alborz and Chaharmahal and Bakhtiari Provinces

Estimation of crop water requirement and evapotranspiration by lysimeter is costly and time-consuming and could not be applied to larger field scale. Remote sensing technology can overcome this limitation. The goal of this research was to estimate alfalfa actual evapotranspiration using satellite imagery and compare it with the in-situ measurement by lysimeter. The study was carried out from 2017 to 2020 in the agricultural lands of Alborz and Charmahal and Bakhtiari provinces employing Surface Energy Balance Algorithm for Land (SEBAL) method. Lysimeter has been implemented under standard conditions. The cold pixels of each satellite image were extracted to estimate net alfalfa crop water requirement. In-situ net crop water requirement for Alborz and Charmahal and Bakhtiari provinces were obtained as 1383 and 1087 mm, respectively. The coefficients of determination (R2) were 73% and 76%, respectively, for the two studied provinces. The statistical analysis showed that there were small deviations from the mean values. The standard evapotranspiration measurements using lysimeter were higher than the satellite estimations. This technique can be useful for the estimation of crop water consumption since it is simple, cheap, fast, and can be used for large areas.