EVALUATION OF A MODEL TO ESTIMATE NET RADIATION OVER A DRIP-IRRIGATED OLIVE ORCHARD USING LANDSAT SATELLITE IMAGES

Satellite-based remote sensing tools estimate crop water requirements based on surface energy balance, where the net radiation (R_n) is the most important factor. In this regard, a study was carried out to validate the METRIC (Mapping EvapoTranspiration at high Resolution with Internalized Calibration) model for estimating instantaneous values of net radiation (R_ni) over a drip-irrigated olive orchard which is located in the Pencahue Valley, Maule Region, Chile (lat. 35°23’S; long. 71°44’W; 96 m above mean sea level). The performance of the METRIC model to compute R_ni was carried out using ground-based measurements of net radiation at the time of satellite overpass (11:28 h). For this study, 12 landsat images were acquired during clear sky days between 2009 and 2012. The statistical analysis indicated that the METRIC model underestimated the values of R_ni by about 3% with a root mean square error (RMSE) and mean absolute error (MAE) of 40 and 33 W m^-2, respectively.