Using combined large-eddy simulation and remote sensing to assess land-atmosphere coupling

Many practical applications of remote sensing, e.g. precision agriculture, require the accurate determination of local and regional influences on the surface energy balance. Traditional methodologies of evaporative flux estimation with remote sensing make the assumption of equilibrium between the local surface and spatially average atmospheric properties (e.g. temperature and humidity) at the pixel scale. Here, we quantify the errors in this assumption by combining a large-eddy simulation (LES) with remotely sensed boundary conditions and applying it to data from the SMEX'02/SMACEX experiment over an agricultural watershed in Iowa. We explore the coupling coefficient concept of Jarvis and McNaughton and determine the impact of local and regional controls on evapotranspiration and land atmosphere coupling. Using data from two days with significantly different vegetation and soil moisture conditions we quantify the magnitude of errors in assuming regional equilibrium.