Estimation of Energy Balance Components over a Drip-Irrigated Olive Orchard Using Thermal and Multispectral Cameras Placed on a Helicopter-Based Unmanned Aerial Vehicle (UAV)

Samuel Ortega-Farías,Richard Allen,Samuel Ortega-Salazar,Carlos Poblete-Echeverría,Tomas Poblete,Ayse Kilic,Mauricio Zuñiga,Daniel Sepúlveda,Luis Ahumada-Orellana

doi:10.3390/rs8080638

Abstract

A field experiment was carried out to implement a remote sensing energy balance (RSEB) algorithm for estimating the incoming solar radiation (Rsi), net radiation (Rn), sensible heat flux (H), soil heat flux (G) and latent heat flux (LE) over a drip-irrigated olive (cv. Arbequina) orchard located in the Pencahue Valley, Maule Region, Chile (35°25′S; 71°44′W; 90 m above sea level). 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 temperature (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 H and LE obtained from an eddy correlation system. In addition, estimated values of Rsi and Rn were compared with ground-truth measurements from a four-way net radiometer while those of G were compared with soil heat flux based on flux plates. Results indicated that RSEB algorithm estimated LE and H with errors of 7% and 5%, respectively. Values of the root mean squared error (RMSE) and mean absolute error (MAE) for LE were 50 and 43 W m−2 while those for H were 56 and 46 W m−2, respectively. Finally, the RSEB algorithm computed Rsi, Rn and G with error less than 5% and with values of RMSE and MAE less than 38 W m−2. Results demonstrated that multispectral and thermal cameras placed on an UAV could provide an excellent tool to evaluate the intra-orchard spatial variability of Rn, G, H, LE, NDVI and Tsurface over the tree canopy and soil surface between rows.

Highlights

Olive orchards have increased significantly in Chile during the last decade, and water scarcity has become the main limitation to maintain olive oil production [1]
The results indicated that the maps at very imagesresolution (NDVI and Tsurface results indicated that the maps at verybalance high spatial high spatial were able).toThe show significant differences between the energy fluxes resolution were able to show significant differences between the energy balance fluxes above thewere tree above the tree canopy and the soil surface between rows
This study indicates that the use of both multispectral and thermal cameras onboard of the unmanned aerial vehicle (UAV) allowed acquisition of high-resolution images to assess the intra-field spatial variability of energy balance components over a drip-irrigated olive orchard under non and moderate water stress conditions

Summary

Introduction

Olive orchards have increased significantly in Chile during the last decade, and water scarcity has become the main limitation to maintain olive oil production [1]. Under these conditions, sophisticated irrigation water management will be required to optimize water productivity (oil production per unit of consumed water, kg m3 ) and to maintain sufficient levels of yield and quality [3,4]. To achieve these targets, it is necessary to have a reliable method to quantify the olive water requirements and actual evapotranspiration (ETa). The accurate estimate of ETa or latent heat flux (LE)

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Conclusion