SAP FLOW METER (SFM1) is crucial in evaluating eddy covariance data

Eddy covariance technique is extensively used in long-term observation networks (e.g. FLUXNET) and provides direct estimates of ecosystem level fluxes of carbon, water and energy. The method, however, has attached uncertainties due to the widely observed lack of energy surface balance closure (EBC) - the mismatch between turbulent energy fluxes (latent heat and sensible heat) and the available energy. Latent heat can be simultaneously measured with independent methods (e.g. sap flow, lysimeter). Recently, Perez-Priego et al., (2017) demonstrated this approach to quantify measurement errors in eddy covariance latent heat and evaluated the underlying factors explaining the lack of energy balance closure in a savanna-type ecosystem.

While understorey latent heat was measured with state-of-the-art lysimeters, stand tree transpiration was estimated by combining sap flow measurements and biometric information of half-hourly tower footprint (i.e. tree density, sapwood area). Sap flow measurements were done using heat ratio technique (Burgess et al, 2001) using SFM1 sensors. Sap flow measurement using the SFM1 (kg m-2 h-1) was converted to latent heat (LE, W m-2).

This study showed a systematic underestimation of latent heat by eddy covariance. It was found that inconsistencies between LE by EC and that estimated with independent methods followed structured patterns under certain environmental conditions. To read more about this research, please click this link.

Special thanks to Dr. Oscar Perez-Priego for the photos and comments.

Dr Beng Umali
Applications & Research Scientist