Calibration of an energy flux model over bare soils during the HAPEX-MOBILHY experiment

Abstract Surface energy fluxes can be evaluated from remotely sensed data using models describing the transfers between soil, vegetation and atmosphere. To be applied over bare soils and over partial canopies for which the soil evaporation is comparable to that from foliage, these models need three key soil parameters (thermal inertia, hydraulic diffusivity, and limit evaporation) which depend strongly on the soil type and on its moisture content. In this paper, classical parameterizations of thermal and hydraulic properties are tested by comparing the simulated fluxes, using a two-reservoir model, with the fluxes observed during the Special Observing Period of the international HAPEX-MOBILHY experiment. It is shown that none of these parameterizations are able to reproduce the observed surface fluxes. To overcome this problem, a methodology is proposed to evaluate these soil parameters in the field by minimizing the difference between observed and simulated surface fluxes. It is based on the adjustment of the soil parameters using measurements of the surfacewater content and of surface fluxes given by micrometeorological stations on representative regional sites. This methodology may be easily applied to remote sensing observations. It requires measurements in the thermal infrared (to deduce the thermal inertia), and in the microwave region (to deduce the hydraulic diffusivity), and micrometeorological networks, able to deliver atmospheric fluxes from representative regional sites (to deduce the limit evaporation).