ESTIMATION OF SENSIBLE HEAT-FLUX OVER SPARSELY VEGETATED SURFACES

The approach of using remote sensing of surface temperature to estimat e spatially distributed surface energy balance components is very attr active. This approach has been applied successfully over surfaces with near full vegetation cover. However, large discrepancies between meas ured and simulated surface fluxes have been observed over surfaces wit h sparse vegetation cover. The reason for these discrepancies is that the assumption that radiative surface temperature can be equated to ae rodynamic surface temperature is not correct over sparsely vegetated s urfaces. In this study an empirical model, relating radiative-aerodyna mic surface temperature difference to radiative-air temperature gradie nt and leaf area index, was used to estimate sensible heat flux over s parse shrub in the Central East supersite during the Hydrologic and At mospheric Pilot Experiment in the Sahel (HAPEX-Sahel) measurement camp aign. The result shows that this parameterization leads to reasonable estimates of sensible heat flux; the root mean square error (RMSE) was about 50 W m(-2) A second data set over sparse cotton in Arizona had a RMSE of about 20 W m(-2). Although the results of this study are enc ouraging, one should be cautious, however, because there is a need for additional investigation of this procedure.