AIRBORNE THERMAL DATA FOR EVALUATING THE SPATIAL-DISTRIBUTION OF ACTUAL EVAPOTRANSPIRATION OVER A WATERSHED IN OCEANIC CLIMATIC CONDITIONS - APPLICATION OF SEMIEMPIRICAL MODELS

Considerable work has been done on estimating daily fluxes at the regi onal scale from thermal data acquired in the early afternoon using sem iempirical models. But these studies have dealt only with clear days a nd homogeneous surfaces. We evaluate the use of some of these models u nder variable climatic conditions. A campaign of micrometeorological m easurements performed from May to October 1993 on a small agricultural catchment in Brittany (NW France) allowed us to monitor the water bud get and fluxes of three characteristical surfaces (meadow, wheat and s tubble field). Thermal images covering the whole catchment were acquir ed on 7 August 1993 using an infrared camera aboard a small aircraft. They were corrected for atmospheric effects with the LOWTRAN 7 model. After geometrical corrections to superimpose these images on a digitiz ed land use map, a mapping of surface fluxes al the catchment scale is proposed and discussed.