Knowledge of crop evapotranspiration is crucial for irrigation decision making. An appropriate, user-friendly and time-efficient means of inferring such information is therefore essential. In this study, a closed hemispherical chamber was instrumented, calibrated and deployed in the field for measuring actual evapotranspiration of a vital pasture species, Tall Fescue (Festuca arundinacea). The pasture crop coefficient (Kc) was calculated from the measured instantaneous evapotranspiration and reference crop evapotranspiration (ETo) for a range of growth stages. Also the relationship between Kc and Normalized Difference Vegetation Index (NDVI) as measured using an active optical sensor was established. Using the FAO dual crop coefficient approach and the hemispherical chamber, a technique for partitioning evapotranspiration components was developed. The components of evapotranspiration in terms of basal crop coefficient (Kcb) and soil evaporation coefficient (Ke) were expressed relative to canopy NDVI and Leaf Area Index (LAI). A theoretical model for estimating transpiration was also developed by scaling up stomatal conductance to canopy level in a controlled glasshouse environment. The model was validated against the measured transpiration.