Eddy Covariance flux errors due to random and systematic timing errors during data acquisition

Modern Eddy Covariance (EC) systems collect high-frequency data (10–20 Hz) via instruments’ digital outputs. While this helps overcome the limits of traditional mixed analog/digital systems, it also introduces the new problem of guaranteeing data synchronicity when the clocks of the involved devices cannot themselves be synchronized, which is often the case with instruments providing data via serial or Ethernet connectivity. By means of a simulation study, we found that in most cases random timing errors can safely be neglected, as they do not impact fluxes to a large extent. On the contrary, realistic systematic timing errors potentially arising in asynchronous systems can lead to flux underestimations as large as 10 %, by means of attenuation of high-frequency flux contributions. We characterize the transfer function of such filters as a function of the error amount and find cut-off frequencies as low as 1 Hz, which means that synchronization errors can dominate high-frequency attenuations in open- and enclosed-path EC systems. In most cases, such timing errors cannot be detected nor quantified a posteriori. Therefore, we suggest testing the ability of prospect EC data logging systems to assure required synchronicity and propose a procedure to implement such a test, which relies on readily available equipment.