Quantifying Turbulence Heterogeneity in a Vineyard Using Eddy-Covariance and Scintillometer Measurements

Scintillometry is a non-invasive measurement technique for acquiring spatially-averaged surface heat and moisture fluxes in areas where setting up arrays of instruments can be expensive and logistically difficult. As a path-averaged measurement, scintillometry is a valuable tool for measuring integrated atmospheric turbulence over agricultural terrain where in situ measurements would interfere with farm operations. For this study, a two-wavelength scintillometry system was deployed at an effective height of 7.3 m above ground spanning 749 m over an active vineyard with a canopy height of approximate to 2.15 m. Four eddy-covariance stations were placed strategically throughout the vineyard to capture any spatial heterogeneity. The stations were used to assess whether the spatially-averaged structure parameters of temperature, (C-T2), and humidity, (C-q2), adhered to Monin-Obukhov similarity theory (MOST). We derive a new metric, D, to quantify the deviation from homogeneity that describes the nonlinear effects in MOST linking structure parameters and fluxes. This deviation metric gives a physical meaning to the apparent flux overestimation of scintillometry discussed in previous literature. It also facilitates the identification of periods when nonlinear effects are minimal. Using D, we show that the vineyard is homogeneous at the spatial scales of the scintillometer path and use another dataset to emphasize the applicability of D to quantify heterogeneity for a variety of composite surfaces.