EVAPORATION FOR MARITIME CATCHMENT COMBINING A METEOROLOGICAL MODEL WITH VEGETATION INFORMATION AND AIRBORNE SURFACE TEMPERATURES

Estimation of daily fluxes at regional scale using thermal infrared da ta through semi-empirical models is problematic under oceanic climates , due to the frequency of cloudy days and the subsequent low availabil ity of thermal infrared images (TIR). The gap between available satell ite information must therefore be bridged by simulation from cropwater balance models. in an experiment on a small agricultural catchment in Brittany (NW France) we have used TIR data and an agrometeorological model to estimate actual evapotranspiration (AET). The model is descri bed: a new module has been added to take into account the canopy devel opment through the LAI variations. Continuous micrometeorological meas urements were made on three characteristic surfaces (meadow, wheal and stubble field). The agrometeorological model simulated correctly the main energy fluxes and the surface temperatures for these changing cli matic conditions. Thermal images covering the whole catchment were acq uired on 6 August 1993 using an airborne infrared camera. The comparis on between the surface temperatures acquired by the camera and the gro und measurements was satisfactory. We discussed the possibilities of c ombining these data with the model to estimate AET at the catchment sc ale.