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In this contribution, we present a simple method based on Albedo-VI (vegetation index) triangular space to determine the Priestley-Taylor parameter for estimating evaporative fraction (EF) and evapotranspiration (ET) in arid and semi-arid regions. We apply this method to MODIS and observation data acquired during the Heihe river basin field experiment from July 1 to September 30, 2008. Results show that the decreasing trend of the estimated EF from MODIS data is consistent with that of precipitation during the period of day 183 to 274, 2008. The bias of estimated daily ET deviating from the corresponding ground-measured ET is -8.66 W/m(2) and the root-mean-square error is 21.55 W/m(2), indicating the Albedo-VI triangular method has a potential in ET estimation as a simple satellite-based method independent of surface ancillary data. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3557817]