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Spatial knowledge of land surface evapotranspiration (ET) is of prime interest for environmental applications, such as optimizing irrigation water use, irrigation system performance, crop water deficit, drought mitigation strategies, and accurate initialization of climate prediction models especially in arid and semiarid catchments where water shortage is a critical problem. The recent drought in Australia and concerns about climate change have highlighted the need to manage water resources more sustainably especially in the Murrumbidgee catchment which utilizes bulk water for food production. This study deals with the application of a Surface Energy Balance System (SEBS) algorithm based on Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) data and field observations has been proposed and tested for deriving ET over Coleambally Irrigation Area, located in the southwest of NSW, Australia. We have used 12 ASTER scenes covering the time period of 2002, 2003, 2004, 2005, 2006, and 2009 for estimating the actual ET over the study area. To validate the proposed methodology, the ground-measured ET was compared to the ASTER-derived actual ET values for the study area. The derived ET value over the study area is much closer to the field measurement. From the remote sensing results and observations, the root mean square error is 0.89 and the mean absolute percentage difference is 2.87 %, which demonstrate the reasonability of SEBS ET estimation for the study area.