Evaluation of a two-source patch model to estimate vineyard energy balance using high-resolution thermal images acquired by an unmanned aerial vehicle (UAV)

The use of unmanned aerial vehicles (UAVs) equipped with high-resolution thermal infrared (TIR) cameras can provide the necessary spatial variability for estimating energy balance (EB) components over heterogeneous canopies, such as those of vineyards. An experiment was carried out to evaluate a two-source patch energy balance (TSPEB) model for computing the net radiation (R-n), sensible heat flux (H), soil heat flux (G), and latent heat flux (LE) over two drip-irrigated vineyards. These vineyards were trained on a vertical shoot-positioned (VSP) system and located in the Molina and Pencahue valleys, Maule Region, Chile (35 degrees 20'L. S, 71 degrees 46'L. W, 86 m.a.s.l.). For this study, a UAV was equipped with a TIR camera to retrieve the surface temperature (T-s) at a very high resolution (6 cm x 6 cm). At the time of the UAV overpass, the meteorological variables and EB components were collected above the vineyard. The TSPEB model was evaluated using the H and LE measurements from an eddy covariance (EC) system. Additionally, the computed values of R-n and G were compared with field measurements from a four-way net radiometer and flux plates, respectively. The results indicated that the TSPEB model estimated R-n, H, G, and LE with errors of 7, 14, 7, and 9%, respectively. For the EB components, the values of the mean square error (RMSE) and mean absolute error (MAE) ranged from 13-75 and 11-61 W m(-2), respectively. The main uncertainties were associated with errors in the estimation of the soil and canopy sensible heat fluxes.