Effects of Path Averaging in a Sonic Anemometer on the Estimation of Turbulence-Kinetic-Energy Dissipation Rates

The turbulence-kinetic-energy dissipation rate is a fundamental property in turbulent flows, but its direct measurement in the atmospheric surface layer is still a challenge. Indirect estimates are often obtained from inertial-subrange laws using turbulence statistics of the longitudinal velocity component. In this study, synthetic turbulence data are used to investigate the impact of path-averaging effects present in sonic anemometer data on the inertial subrange of the second-order structure function. Path averaging reduces the energy levels in the second-order structure function, creating a negative bias in the estimates of the dissipation rate. The effect is dependent on the path-averaging transfer function, mean wind speed and path length. A simple correction for the bias on the basis of existing transfer functions is applied and tested with data obtained from two separate sonic anemometers. Compared to the spectrum, the second-order structure function after the correction becomes the optimum statistical measure for indirect estimation of the dissipation rate, due to its lower random error and insensitivity to aliasing effects.