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A Refinement of the McMillen (1988) Recursive Digital Filter for the Analysis of Atmospheric Turbulence
- Falocchi, Marco, Giovannini, Lorenzo, Franceschi, Massimiliano de, Zardi, Dino
- Boundary-layer meteorology 2018 v.168 no.3 pp. 517-523
- algorithms, landscapes, turbulent flow
- We present a refinement of the recursive digital filter proposed by McMillen (Boundary-Layer Meteorol 43:231–245, 1988), for separating surface-layer turbulence from low-frequency fluctuations affecting the mean flow, especially over complex terrain. In fact, a straightforward application of the filter causes both an amplitude attenuation and a forward phase shift in the filtered signal. As a consequence turbulence fluctuations, evaluated as the difference between the original series and the filtered one, as well as higher-order moments calculated from them, may be affected by serious inaccuracies. The new algorithm (i) produces a rigorous zero-phase filter, (ii) restores the amplitude of the low-frequency signal, and (iii) corrects all filter-induced signal distortions.