Abstract
A field study on a 50-ha alfalfa (Medicago sativa L.) irrigated field was conducted to investigate the performance of the remote sensing (RS) based Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC) model in the estimation of evapotranspiration (ET) under the arid conditions of Saudi Arabia. The METRIC model performance was investigated by comparing the energy fluxes estimated by the model to the output of a surface layer scintillometer (SLS) system installed in the field, given the fact that the SLS is efficient in measuring sensible heat fluxes (H) over vegetative areas. Landsat-8 reflectance data were used as inputs for the METRIC model. Results of the study revealed that the H-METRIC data was strongly correlated with the H-SLS data with an R-2 value of 0.74 (P > F = 0.0064) and a mean bias error (MBE) of 6.05 W m(-2) (6 %). The METRIC model showed a good performance in estimating the hourly latent heat (LE) fluxes compared with SLS data with an R2 value of 0.81 (P > F = 0.0023), an MBE of 24.46 W m(-2) (8 %) and a Nash-Sutcliffe efficiency (NSE) of 0.91. Furthermore, the hourly ET was estimated with an MBE and an NSE of 0.036 mm h(-1) (8 %) and 1.00, respectively. Compared to the SLS data, the METRIC model was found to generally provide an efficient and an accurate means of energy fluxes estimation; therefore, ET estimation over the studied irrigated alfalfa crop.