ABSTRACT
Determination of evapotranspiration (ET) is important for evaluation of hydrologic resources of a region, and evaluating irrigation requirements. Because of the interrelation between components of the hydrologic cycle, ET is important in the evaluation of soil water content, surface runoff, and aquifer recharge. ET is defined as the combination of evaporation from soil and plant surfaces, and transpiration from plant leaves. Evaporation is the process whereby liquid water is converted to water vapor and removed from the evaporating surface [3]. Transpiration is the vaporization of liquid water contained in plant tissues and its subsequent removal to the atmosphere. Crops predominately lose water through small openings in their leaves called stomata. ET can be expressed in units of mm/day (or in/day), or as an energy flux in units of MJ m-2 day-1 [3]. ET is important because it is often the largest component of the hydrologic cycle after rainfall. Under arid conditions, potential ET can easily exceed rainfall. Remote sensing methods for estimating ET are needed for tropical conditions. Various techniques have been developed based on radiation methods [e.g., 20] and surface energy budgets [e.g., 1 and 5].
