Estimation and partitioning of actual daily evapotranspiration at an intensive olive grove using the STSEB model based on remote sensing

This study is based on the application of an existing simplified two-source energy balance (STSEB) model, using medium-resolution satellite imagery (Landsat) to estimate instantaneous (at the satellite overpass time) and daily actual crop evapotranspiration (ETa) over an intensive olive grove. Daily values were obtained by the use of the evaporative fraction method and corrected for latent heat, available energy, and evaporative fraction biases (beta-factor correction). Model estimates were compared to ground-based measurements. Heat flux densities (eddy covariance method) were recorded, and five Landsat images at approximately monthly intervals were used, covering our study site in 2011. Comparison with ground measurements showed a maximum difference of -0.6 mm day(-1) before, and 0.2 mm day(-1) after beta-factor correction for the main plot. The experimental site consisted of a main plot exposed to deficit irrigation, and two small subplots where during a limited period of time (six weeks) one was temporarily not irrigated, and the other well irrigated for reference. One Landsat image was available for this limited period of time. Additionally, the STSEB algorithm was tested for partitioning evapotranspiration into its evaporation and transpiration components. Evaporation estimated from the STSEB model was compared with evaporation estimated from a model adjusted from local lysimeter measurements. Transpiration data obtained from calibrated sap flow measurements were, after local calibration, also compared to model estimates. Model results agreed with the measured data, showing) under- and overestimation for transpiration and evaporation, respectively.