De-spiking parameters: Difference between revisions
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The shear probe will collide with plankton and other particulates in the water, and it will occasionally hit jellyfish and even some fish that do not get out of its path. These collisions cause a very large and transient signal from the shear probe. These anomalies typically last for ~50ms, but can be longer in the case of jellyfish. They do not represent shear and bias high the variance of shear and the rate of dissipation. These anomalies should be replaced with data of constant value and the data so modified must be tracked because it is a quality control metric. | The shear probe will collide with plankton and other particulates in the water, and it will occasionally hit jellyfish and even some fish that do not get out of its path. These collisions cause a very large and transient signal from the shear probe. These anomalies typically last for ~50ms, but can be longer in the case of jellyfish. They do not represent shear and bias high the variance of shear and the rate of dissipation. These anomalies should be replaced with data of constant value and the data so modified must be tracked because it is a quality control metric. | ||
If more than a few percent of the data used for a particular estimate of <math>\varepsilon</math> have been modified by the de-spiking algorithm than such estimates are suspect. | |||
A widely used [[de-spiking algorithm]] identifies shear-probe signal anomalies by comparing the absolute shear against a smoothed version of the absolute shear. | A widely used [[de-spiking algorithm]] identifies shear-probe signal anomalies by comparing the absolute shear against a smoothed version of the absolute shear. | ||
It requires a threshold and smoothing parameter and the number of points to be replaced around a spike. | It requires a threshold and smoothing parameter and the number of points to be replaced around a spike. | ||
You may use other de-spiking algorithms but it important to keep track of the fraction of the data that has been modified. | |||
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return to [[Flow chart for shear probes]] | return to [[Flow chart for shear probes]] | ||
Revision as of 21:55, 18 November 2021
The shear probe will collide with plankton and other particulates in the water, and it will occasionally hit jellyfish and even some fish that do not get out of its path. These collisions cause a very large and transient signal from the shear probe. These anomalies typically last for ~50ms, but can be longer in the case of jellyfish. They do not represent shear and bias high the variance of shear and the rate of dissipation. These anomalies should be replaced with data of constant value and the data so modified must be tracked because it is a quality control metric. If more than a few percent of the data used for a particular estimate of [math]\displaystyle{ \varepsilon }[/math] have been modified by the de-spiking algorithm than such estimates are suspect.
A widely used de-spiking algorithm identifies shear-probe signal anomalies by comparing the absolute shear against a smoothed version of the absolute shear. It requires a threshold and smoothing parameter and the number of points to be replaced around a spike. You may use other de-spiking algorithms but it important to keep track of the fraction of the data that has been modified.
return to Flow chart for shear probes
