Satellite-based evapotranspiration of a super-intensive olive orchard: Application of METRIC algorithms

Abstract

METRIC™is a satellite-based surface energy balance model aimed at estimating and map-ping crop evapotranspiration (ET). It has been applied to a large range of vegetation types,mostly annual crops. When applied to anisotropic woody canopies, such as olive orchards,extensions are required to algorithms for estimating the leaf area index (LAI), surfacetemperature, and momentum roughness length (Zom). The computation of the radiometricsurface temperature needs to consider a three-source condition, thus differentiating thetemperature of the canopy (Tc), of the shaded ground surface (Tshadow), and of the sunlitground surface (Tsunlit). The estimation of theZomfor tall and incomplete cover is basedupon the LAI and crop height using the Perrier equation. The LAI,Zom, and temperaturederived from METRIC after these adjustments were tested against field collected data withgood results. The application of METRIC to a two year set of Landsat images to estimate ET ofa super-intensive olive orchard in Southern Portugal produced good ET estimates thatcompared well with ground-based ET. The analysis of METRIC performance showed aquantitative improvement of ET estimates when applying the three-source condition fortemperature estimation, as well as theZomcomputation with the Perrier equation. Resultsshow that METRIC can be used operationally to estimate and mapping ET of super-intensiveolive orchards aiming at improving irrigation water use and management.