Crop coefficients and actual evapotranspiration of a drip-irrigated Merlot vineyard using multispectral satellite images

A field experiment was carried out to evaluate the METRIC (mapping evapotranspiration at high resolution with internalized calibration) model to estimate the actual evapotranspiration (ETa) and crop coefficient (K (c)) of a drip-irrigated Merlot vineyard during the 2007/2008 and 2008/2009 growing seasons. The Merlot vineyard located in the Talca Valley (Chile) was trained on a vertical shoot positioned system. The performance of METRIC was evaluated using measurements of ETa and K (c) from an eddy covariance (EC) system. METRIC overestimated ETa by about 9 % with a root mean square error (RMSE) and mean absolute error (MAE) of 0.62 and 0.50 mm d(-1), respectively. For the main phenological stages of the Merlot vineyard, METRIC overestimated the K (c) by about 10 % with RMSE = 0.10 and MAE = 0.08. Furthermore, the indexes of agreement were 0.70 for K (c) and 0.85 for ETa. Mean values of K (c) measured from EC were 0.41, 0.53, 0.56, and 0.46, while those estimated by METRIC were 0.46, 0.54, 0.59, and 0.62 for the bud break to flowering, flowering to fruit set, fruit set to veraison, and veraison to harvest stages, respectively.