Aerodynamic Temperature Derived From Flux-Profile Measurements and Two-Source Model Predictions Over a Cotton Row Crop in An Advective Environment.

The surface aerodynamic temperature (SAT) is related to the atmospheric forcing (radiation, wind speed and air temperature) and surface conditions. SAT is required in the bulk surface resistance equation to calculate the rate of sensible heat flux exchange. SAT cannot be measured directly and therefore is often replaced with a remotely-sensed surface temperature using a one-source energy balance modeling approach. However, field studies have shown that the relationship between aerodynamic and radiometric surface temperature is affected by many factors (e.g., leaf area index and surface heterogeneity), especially for partial-canopy surfaces, and hence significantly affects sensible heat flux estimation using flux-gradient approaches. In this study, SAT for a cotton crop was estimated using wind and temperature profile measurements along with eddy covariance measurements of turbulent heat and momentum fluxes.  A two-source (soil + vegetation) energy balance model using radiometric surface temperature also provides an estimate of the aerodynamic temperature when solving for the canopy and soil temperatures and turbulent exchange of the soil and vegetation components under the imposed atmospheric forcing conditions. A comparison is made using flux-profile methods to estimate SAT, empirical equations derived from field measurements, and the two-source energy balance model estimates. Implications of the aerodynamic-surface radiometric temperature relationship on the estimation of sensible heat flux and evapotranspiration, using remotely sensed surface temperature under the BEAREX08 field conditions, will be discussed.