Quantification of evapotranspiration is of great importance for hydrological and meteorological modeling and indispensable for water management of irrigated crops. In this sense the main objective of this study was the estimation of actual daily evapotranspiration (Etr), in local and regional scale, utilizing the SEBAL (Surface Energy Balance Algorithm for Land). The TM - Landsat 5 images and weather data were used in order to assess the energy balance components. The studied area is located in Cariri region, Ceará State, and is composed by irrigated areas, native vegetation and part of the Chapada do Araripe Reserve. Four TM - Landsat 5 images of September 29th, October 15th, October 31st and November 16th of 2005, were used. Daily ETr was estimated based on the density of latent heat flux, obtained as residue of the energy balance equation. The application of the SEBAL algorithm includes some steps as radiometric calibration, estimation of the reflectance and albedo, emissivity and vegetation index, based on the reflective bands of the orbital sensors and further on the surface temperature (thermal band) for the TM - Ladsat 5. Two irrigated fields of castor bean and cotton were used do validated the ETr estimated values. The reference evapotranspiration was obtained by FAO-Penman-Monteith method. The mean daily ETr over the studied area presented values of 3.8, 3.7, 4.6 and 3.4 mm.dia-1 on 29/09, 15/10, 31/10 and 16/11, respectively. When compared to measured data in the castor bean (Ricinus communis L.) and cotton (Gossypium hirsutum) irrigated crops, the ETr values obtained with SEBAL present differences smaller than 1,0 mm day-1, showing its importance and accuracy.
Spectral radiance; energy balance; actual evapotranspiration; SEBAL
