Performance of the METRIC model for mapping energy balance components and actual evapotranspiration over a superintensive drip-irrigated olive orchard

A field experiment was performed to evaluate the Mapping Evapotranspiration at High Resolution using Internalized Calibration (METRIC) model that was used for mapping surface energy balance (SEB) components (net radiation (Rn_i), soil heat flux (G_i), sensible heat flux (H_i), and latent heat flux (LE_i)) at times of Landsat satellite overpasses in conjunction with the actual evapotranspiration (ETa) and crop coefficient (Kc) for a superintensive, drip-irrigated olive (Olea europeae L. cv Arbequina) orchard. The orchard is located in the Pencahue Valley, Maule Region, Chile (35 23' LS; 71 44' LW; 96 m above sea level), and the study was conducted on an experimental plot of 21.1 ha during the 2011/2012 and 2012/2013 growing seasons. Model performance was evaluated using measurements of LE_i, ETa and Kc that were obtained from an eddy covariance (EC) system. Olive-specific functions for estimating aerodynamic roughness (z_om), leaf area index (LAI), and G_i were employed in the METRIC algorithm. In addition, submodels of Rn_i and G_i were evaluated via ground-truth measurements from a Fritchen-type net radiometer and soil flux plates, respectively. The results indicated that the errors within the METRIC model for the SEB components were between 2% and 5% of the observed values, while those for ETa and Kc were between 4% and 6% of the EC values. In addition, both the root mean square error (RMSE) and mean absolute error (MAE) for the SEB components were less than 46 W∙m⁻² at the times of satellite overpass. The RMSE and MAE values for the 24-h ETa were 0.42 and 0.31 mm·day⁻¹, respectively, while the corresponding values for Kc were 0.09 and 0.02, respectively. The coefficients of variation (CVs) for the SEB components, ETa and Kc were less than 15%, and the largest intraorchard spatial variability occurred for LE_i and, thus, ETa. The errors and uncertainties in the SEB and ETa estimates were small enough to warrant application of the METRIC model with olive-specific functions for z_om, LAI and G_i to superintensive drip-irrigated olive orchards.