Velocity despiking: Difference between revisions
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Spikes in velocities measured by [[Acoustic-Doppler Velocimeters| 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">{{Cite journal|authors= D. G. Goring and V.I. Nikora|journal_or_publisher= Journal of Hydraulic Engineering|paper_or_booktitle= Despiking Acoustic Doppler Velocimeter Data | Spikes in velocities measured by [[Acoustic-Doppler Velocimeters| 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">{{Cite journal|authors= D. G. Goring and V.I. Nikora|journal_or_publisher= Journal of Hydraulic Engineering|paper_or_booktitle= Despiking Acoustic Doppler Velocimeter Data | ||
|year= 2002|doi= 10.1061/ASCE0733-94292002128:1117}}</ref>. | |year= 2002|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 [[Velocity inertial subrange model|inertial subrange model]]. | ||
[[File:Despike spectra.png|thumb|Example velocity spectra before and after removing spikes. The variance of the despiked signal has reduced by 12% even though there were 30 spikes]] | |||
== Despiking methods == | == Despiking methods == | ||
Revision as of 19:11, 24 November 2021
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 [1]. 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 [1]. Other techniques currently being investigated by the subgroup are those used in atmospheric turbulence studies [2], in particular the median filter despiking technique [3], which derives its threshold for identifying spurious spikes from the data itself.
Filter based methods
Phase-space thresholding methods
Elaborate a bit? Or include information in a separate page
Notes
- ↑ Jump up to: 1.0 1.1 D. G. Goring and V.I. Nikora. 2002. Despiking Acoustic Doppler Velocimeter Data. Journal of Hydraulic Engineering. doi:10.1061/ASCE0733-94292002128:1117
- ↑ D. Starkenburg, S. Metzger, G.J. Fochesatto, J.G Alfieri, R. Gens and A. Prakash and J. Cristobal. 2016. Assessment of Despiking Methods for Turbulence Data in Micrometeorology. J. Atmos. Oceanic Technoly. doi:10.1175/JTECH-D-15-0154.1
- ↑ F.V. Brock. 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
