Abstract:
Accurate measurements of evapotranspiration and of energy fluxes between the land and the atmosphere are very important in understanding climatic patterns. Several techniques and models can measure heat fluxes and evapotranspiration including scintillometers and eddy covariance systems. In this experiment, measurements of sensible and latent heat fluxes were carried out using a boundary layer scintillometer (BLS 900) installed along an open path eddy covariance in a semi-arid climate at a vineyard located in the Beqaa valley, Lebanon. The results showed good correlation between the sensible heat flux estimates measured by both systems, sensible heat flux measured by the eddy covariance system was less than the one measured by the scintillometer by 14.13%. This difference decreased when the surface energy balance closure ratio was closer to 1 (11.12%), wind direction was perpendicular to the scintillometer beam pass (9.62%) and with high wind speed at the experimental site location (6.87%). Sensible heat fluxes measured by both systems showed better agreement when the bare soil to leaves ratio was low (Period of low NDVI). Additionally, sensible heat fluxes measured by both systems were lower during major rainfall events at the experimental site location. Good correlation was also found when comparing latent heat fluxes (LE) estimated by both systems, latent heat flux estimated by the eddy covariance system was lower than the one estimated by the scintillometer by 5%. This difference in the latent heat flux measured by each system is attributed to errors in the energy balance closure error, and to discrepancies in the net radiation or ground heat flux estimates as they are point measurements. Differences in the footprint of each system was not a major cause in the discrepancies in fluxes measured during this experiment as the source area of both systems share the same soil surface characteristic.
