The researchers studied how to accurately estimate daily evapotranspiration using hourly data. They used measures of latent heat flux and sap flow transpiration to validate a surface energy balance model. By analyzing images of an olive orchard taken at different times and resolutions, they found that a pixel size similar to the canopy size was best for estimating evapotranspiration. They also discovered a time lag between latent heat flux from the canopy and sap flow at the tree trunk. The study suggests that sap flow transpiration can be used to measure surface energy balance on a daily basis or when images are taken near noon.