Extension to 3D of “The Effect of Line Averaging on Scalar Flux Measurements with a Sonic Anemometer near the Surface” by Kristensen and Fitzjarrald

Abstract

Here, the theory of Kristensen and Fitzjarrald, for the transfer function of sonic anemometers for vertical scalar fluxes, is extended from anemometers that use one vertically oriented acoustic path to measure the vertical velocity, to anemometers where the signals measured along three independent paths are involved in the estimation of the vertical velocity. It is found that sonics involving three axes give a significantly stronger attenuation of the small-scale contributions to the flux, than sonics with a vertical acoustic path. This effect should therefore be taken into account when a three-axis sonic anemometer is used to estimate vertical fluxes.