Modelling evapotranspiration by remote sensing parameters and agro-meteorological stations.

Field energy balances from irrigated and natural ecosystems, together with a net of agrometeorological stations, were used to develop a model for actual evapotranspiration (ET) quantification, based on the ratio of actual to reference evapotranspiration and the relation of this ratio to remote sensing parameters. The model was applied in the Brazilian semi-arid region to analyse the regional ET, making use of Landsat images and a geographic information system. After comparison against field results1 it showed good agreement, explaining 89% ofthe variances and a mean square error (RMSE) ofO.34 mm d