Velocity despiking
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Overview
Any measured signal may be contaminated by spikes. These spikes are typically short-lived and transient, which result in sudden change in the measured signal.
Spikes in velocities measured by acoustic-Doppler velocimeters can result from aliasing of the Doppler signal, in particular when pulses become contaminated by reflecting from complex objects and boundaries <ref name="GoringNikora"> {{#arraymap:D. G. Goring and V.I. Nikora|,|x|x|, |and}}. 2002. Despiking Acoustic Doppler Velocimeter Data. Journal of Hydraulic Engineering. doi:10.1061/ASCE0733-94292002128:1117 </ref>. These spikes must be removed because they can alter quite dramatically the velocity spectra, which is then used for fitting inertial subrange model.
Despiking methods
Several techniques exist for despiking. The most used with acoustic-Doppler velocimeters are the phase-space thresholding techniques <ref name="GoringNikora"/>. Other techniques currently being investigated by the subgroup are those used in atmospheric turbulence studies <ref name="Starkenburg"> {{#arraymap:D. Starkenburg, S. Metzger, G.J. Fochesatto, J.G Alfieri, R. Gens, A. Prakash and J. Cristobal|,|x|x|, |and}}. 2016. Assessment of Despiking Methods for Turbulence Data in Micrometeorology. J. Atmos. Oceanic Technoly. doi:10.1175/JTECH-D-15-0154.1 </ref>, in particular the median filter despiking technique <ref name="Brock"> {{#arraymap:F.V. Brock|,|x|x|, |and}}. 1986. A nonlinear filter to remove impulse noise from meteorological data. J. Atmos. Oceanic Technoly. doi:10.1175/1520-0426(1986)003,0051:ANFTRI.2.0.CO;2 </ref>, which derives its threshold for identifying spurious spikes from the data itself.
Filter based methods
Phase-space thresholding methods
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Notes
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