Comparison of Sensible Heat Flux Measurements by a Large Aperture Scintillometer and Eddy Correlation Methods

The eddy correlation (EC) method has been recommended as one of the standard methods for measuring actual evapotranspiration. One of the challenges in interpreting eddy correlation measurements is that the balance between various energy components measured and the total energy received can sometimes be off by up to 30%. An independent measurement of sensible heat flux by scintillometry is often used to resolve this energy balance closure problem. An EC system was set up at a 47 ha commercial corn field in southeastern North Dakota in 2008. Net radiation, latent heat flux, sensible heat flux, soil heat flux and other weather parameters were measured continuously at a 30-min interval during the growing season. A Scintec Boundary Layer Scintillometer 900 (BLS900) was temporarily deployed for seven days when clear sky conditions were satisfied. During the synchronous experiment, both systems were adjusted to at least 1 m above the canopy and collected data at an increased frequency of every minute. The EC system was placed at approximately the midpoint of the scintillometer path. The comparison of sensible heat fluxes measured by the two methods showed good agreement. The results will be used to validate the eddy correlation system in an attempt to reconcile the closure of energy balance.