Vibration-coherent noise removal: Difference between revisions
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The shear probe, like nearly all other velocity sensors, measures the velocity of the fluid relative to the platform that holds the probe. | The shear probe, like nearly all other velocity sensors, measures the velocity of the fluid relative to the platform that holds the probe. | ||
Thus, platform vibrations induce a signal that is due to platform motions and does not represent environmental shear. | Thus, platform vibrations induce a signal that is due to platform motions and does not represent environmental shear. | ||
The algorithm described by Goodman et al (2006)<ref> Goodman, L., Levine, E. R., & Lueck, R. G. (2006). On measuring the terms of the turbulent kinetic energy budget from an AUV. Journal of Atmospheric and Oceanic Technology, 23(7), 977-990. </ref> is often used to remove vibration-induced components from shear-probe spectra. | The [[The_Goodman_algorithm|algorithm]] described by Goodman et al (2006)<ref> Goodman, L., Levine, E. R., & Lueck, R. G. (2006). On measuring the terms of the turbulent kinetic energy budget from an AUV. Journal of Atmospheric and Oceanic Technology, 23(7), 977-990. </ref> is often used to remove vibration-induced components from shear-probe spectra. | ||
This algorithm estimates the transfer functions that relate the vibration (or acceleration) signals to the shear-probe signals. | This algorithm estimates the transfer functions that relate the vibration (or acceleration) signals to the shear-probe signals. | ||
Like all transfer function estimates, the algorithm relies on the coherency between the shear-probe and vibration signals in order to achieve a statistically significant estimate of the transfer functions among these signals. | Like all transfer function estimates, the algorithm relies on the coherency between the shear-probe and vibration signals in order to achieve a statistically significant estimate of the transfer functions among these signals. | ||
Revision as of 22:33, 29 November 2021
All platforms vibrate. The shear probe, like nearly all other velocity sensors, measures the velocity of the fluid relative to the platform that holds the probe. Thus, platform vibrations induce a signal that is due to platform motions and does not represent environmental shear. The algorithm described by Goodman et al (2006)[1] is often used to remove vibration-induced components from shear-probe spectra. This algorithm estimates the transfer functions that relate the vibration (or acceleration) signals to the shear-probe signals. Like all transfer function estimates, the algorithm relies on the coherency between the shear-probe and vibration signals in order to achieve a statistically significant estimate of the transfer functions among these signals. The statistical significance increases with increasing number of fft-segments used to make a spectral estimate. However, this removal biases the spectrum of shear low, in a wavenumber-independent manner, and must be corrected [2]. The bias equals the number of vibration (or acceleration) signals divided by the number of fft-segments used in an estimate of the shear spectrum.
A desire to achieve a high spatial resolution of [math]\displaystyle{ \varepsilon }[/math]-estimates by using short lengths of data with few fft-segments conflicts with the need to achieve good statistical reliability of the transfer function and, thus, the correction for vibration induced signals.
References
- ↑ Goodman, L., Levine, E. R., & Lueck, R. G. (2006). On measuring the terms of the turbulent kinetic energy budget from an AUV. Journal of Atmospheric and Oceanic Technology, 23(7), 977-990.
- ↑ Lueck, R. G., 2022: The bias in coherent-noise removal. Journal of Atmospheric and Oceanic Technology –, submitted, doi:--.
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