Search

Models used for the remote estimation of evapotranspiration are evaluated using aircraft observations over two distinct vegetation regimes in southwestern Australia. Single-source models using an empirically determined excess resistance term performed better than a two-source model, which does not require such a parameterization. The mean absolute difference between measured and estimated values of the sensible heat flux is below 17 W m−2 in comparison with approximately 40 W m−2 for evapotranspiration. Estimates of evapotranspiration depend on the closure of the surface energy balance and incorporate all residual errors in this closure. All models performed better over the agricultural vegetation than over the native vegetation.

A modified soil-canopy-boundary layer model based on Ek and Mahrt is presented to simulate surface heat fluxes on a daily basis. The model is validated against independent published bare soil data from Agassiz, Canada, and observations taken over sparse and dense vegetation as part of the HAPEX-MOBILHY (Hydrological Atmospheric Pilot Experiment-Modelisation du Bilan Hydrique) experiment. Simulated surface energy components are shown to be in close agreement with the observations, and the sensitivity of the parameterization is evaluated.

A model is developed to evaluate surface heat flux densities using the radiant surface temperature and red and near-infrared reflectances from the NOAA Advanced Very High Resolution Radiometer sensor. Net radiation is calculated from an empirical formulation and albedo estimated from satellite observations. Infrared surface temperature is corrected to aerodynamic surface temperature in estimating the sensible heat flux and the latent flux is evaluated as the residual of the surface energy balance. When applied to relatively homogeneous agricultural and native vegetation, the model yields realistic estimates of sensible and latent heat flux density in the surface layer for cases where either the sensible or latent flux dominates.