We propose a multiple regression model is to estimate the monthly reference evapotranspiration (ETo), on a regional scale, from data provided by the MODIS (Moderate Resolution Imaging Spectroradiometer) sensor on board the TERRA satellite platform. The input data assumed by the model are the Normalized Difference Infrared Index (NDII) and the earth's surface temperature, described by the equation
ETo=A×NDII+B×Ts+C (mmmonth)
The model was applied in twelve meteorological stations located at different points in the Araucanía Region, Chile, and resulted in the satisfactory measurement of ETo , obtaining R2=0.87, RM��E=24.84, MAE=19.42 between the observed and estimated data. The model was validated with the Curacautín and Freire stations, obtaining R2=0.82 yR2=0.78 respectively.