Spatialization of sensible heat flux over a heterogeneous landscape

Two methods for retrieving sensible heat flux over a bare soil/wheat composite surface are compared. The first one is based on field measurements using large aperture scintillometers. The comparison with reference fluxes obtained from eddy correlation technique shows that scintillometry-derived fluxes are overestimated by 10%. A numerical experiment demonstrates this is induced by the non-uniform sensitivity of the scintillometer to C-N(2) along the path length which follows a 'bell-shaped' curve. The second method is based on the use of a simple surface energy balance model, SEBAL, supplied with high spatial resolution remote sensing data from two airborne sensors in visible, near infrared and TIR bands. A comparison with scintillometry-derived fluxes shows important discrepancies. These result from large errors in the estimation of the roughness length z(o) in the model. This demonstrates that the use of an empirical relationship based on NDVI only is inadequate for inferring this key parameter in SEBAL.