Various aspects of the measurement and modelling of surface energy fluxes have been studied with particular emphasis on the use of satellite data for the monitoring of fluxes and on their representation in large scale atmospheric models.
The main objective was to carry out a small field experiment in the Sahelian region of the Republic of Niger which would contribute to the design of much larger international experiments in semiarid environments. The influence of local minor surface irregularities on the surface energy fluxes and on their measurement was investigated. At the same time measurements of the radiative properties of the different surface types which characterise the area were made to allow the interpretation of satellite data over this region. The experiment showed that even gradients of only a few percent gave rise to significant changes in the local surface energy fluxes and caused problems with some of the techniques commonly used to measure heat fluxes.
The measurements of the radiative properties of the different soils showed that in the thermal infrared band the split window techniques should be used with extreme caution. In the visible and near visible bands a large variation in the reflectivity of the soil is found. This is important when using satellite data to estimate amount of vegetation in the conditions of sparse cover typical of the Sahel. The work has cast some new light on the problems of area measurements of the surface energy budget and the results are being incorporated into the design of the large international experiments which will take place in southern Europe and Africa in the next few years.
Funding SchemeCSC - Cost-sharing contracts