Estimating Vine Evapotranspiration Using Multispectral and Thermal Sensors Placed aboard an Unmanned Aerial Vehicle
Samuel Ortega-Farias,* Wladinir Esteban, Tomás Poblete, Fernando Fuentes, Camilo Riveros, Luis Ahumada, and Matthew Bardeen
*Universidad de Talca, Citra-Utalca, Avenida Lircay s/n, Casilla 410, Chile (email@example.com)
A field experiment was carried out to implement a remote sensing energy balance (RSEB) algorithm to estimate spatial variability of vine water requirements or evapotranspiration (ET) over a drip-irrigated Cabernet Sauvignon vineyard located in the Pencahue Valley in the Maule Region, Chile (35°25´ LS; 71°44´ LW; 90 m asl). For this study, a helicopter-based unmanned aerial vehicle (UAV) was equipped with multispectral and infrared thermal cameras to obtain simultaneously the normalized difference vegetation index (NDVI) and surface tem-perature (Tsurface) at very high resolution (6 cm × 6 cm). Meteorological variables and surface energy balance components were measured at the time of the UAV overpass, near solar noon. The performance of the RSEB algorithm was evaluated using measurements of ET from an eddy correlation system. The RSEB algorithm overestimated ET by ~13% with a root mean squared error and mean absolute error of 0.43 and 0.29 mm/day, respectively. Major errors were associated with the estimation of sensible heat flux from the canopy and soil, especially when the wind speed was greater than 2.5 m/sec. Results demonstrated that multispectral and thermal cameras placed on an UAV could provide an excellent tool to evaluate the intravineyard spatial variability of ET.
Funding Support: Chilean National Science Foundation