Abstract
The assessment of evapotranspiration (ET) is of primary interest, especially for agricultural and environmental issues. Traditional micrometeorological techniques require homogenous surface and are characterized by limited footprint. Thus, they cannot be applied to assess ET over inhomogeneous and extensive surfaces, typical conditions at the catchment scale and of extensive farming systems. In this context, a suitable technique to measure turbulent fluxes is scintillometry, which can give measurements of sensible heat flux at larger scale, providing averages over heterogeneous surfaces. ET can then be estimated as residual of the energy budget. In this study, we present results from a one-week campaign held during summer 2016 in Southern Italy. We deployed a Large Aperture Scintillometer (LAS) in an extensive vineyard of 140 ha on a path length of 760 m. The site was characterized by gently slope terrain with uniform crop. In order to have reference measurements of local sensible heat flux, we deployed three sonic anemometers along the scintillometer path. The aim of the study was to test the ability of scintillometry to provide a spatially averaged flux, representative of the possibly diverse conditions in an extended footprint upwind to the measurement path. The relationship between sensible heat flux measured by EC and LAS showed to be very good for the EC station in the middle of the path, whereas off-centre areas were less represented.
Highlights
Evapotranspiration (ET) measurement over inhomogeneous and extensive surfaces ‒ typical conditions at the catchment scale ‒ is still challenging due to spatial variability of vegetation, soil conditions and land topography
If the terrain is undulated, as it is at our site, zeff will vary along the path and an average value should be calculated multiplying the beam distance from d at several points along the path by a specific coefficient obtained from a path weighting function (PWF), as indicated in Scintec Scintillometers Theory Manual, vs 1.04
The sensible heat fluxes derived from Large Aperture Scintillometer (LAS) (HLAS) and measured by eddy covariance (EC) (HEC) showed in general good agreement
Summary
Evapotranspiration (ET) measurement over inhomogeneous and extensive surfaces ‒ typical conditions at the catchment scale ‒ is still challenging due to spatial variability of vegetation, soil conditions and land topography. Traditional micrometeorological techniques, e.g. eddy covariance (EC), cannot be applied under these conditions, requiring homogenous surface and being characterized by limited footprint. In this context, a suitable technique to measure turbulent fluxes is scintillometry, which can give measurements of sensible heat flux (H) at larger scale, providing averages over heterogeneous surfaces. The first scintillometry measurements over vineyards were performed when the method was still experimental [3].
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