Processing your ADCP data using structure function techniques: Difference between revisions
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[[File:ADCPschematic SF.png|thumb|Schematic showing along-beam distance <math> r </math> and radial velocities. ]] | [[File:ADCPschematic SF.png|thumb|Schematic showing along-beam distance <math> r </math> and radial velocities. ]] | ||
# Extract or compute the [[along-beam bin center | # Extract or compute the [[along-beam bin center distance]] [<math>r_0</math>] based on the instrument geometry | ||
# Calculate the [[along-beam velocity fluctuation]] time-series in each bin <math>n</math>, where [<math>v’(n, t)</math>] from the along-beam velocity data that has met the QC criteria (i.e. the data in Level 2 of the netcdf file) | # Calculate the [[along-beam velocity fluctuation]] time-series in each bin <math>n</math>, where [<math>v’(n, t)</math>] from the along-beam velocity data that has met the QC criteria (i.e. the data in Level 2 of the netcdf file) | ||
# Select the maximum distance (<math>r_{max}</math>) over which to compute the structure function based on conditions of the flow (e.g., expected max overturn). The corresponding number of bins is [<math>n_{\text{rmax}} = r_{max} / r_0</math>] | # Select the maximum distance (<math>r_{max}</math>) over which to compute the structure function based on conditions of the flow (e.g., expected max overturn). The corresponding number of bins is [<math>n_{\text{rmax}} = r_{max} / r_0</math>] | ||
Revision as of 10:35, 10 December 2021
To calculate the dissipation rate at a specific range bin and a specific time ensemble:
- Extract or compute the along-beam bin center distance [[math]\displaystyle{ r_0 }[/math]] based on the instrument geometry
- Calculate the along-beam velocity fluctuation time-series in each bin [math]\displaystyle{ n }[/math], where [[math]\displaystyle{ v’(n, t) }[/math]] from the along-beam velocity data that has met the QC criteria (i.e. the data in Level 2 of the netcdf file)
- Select the maximum distance ([math]\displaystyle{ r_{max} }[/math]) over which to compute the structure function based on conditions of the flow (e.g., expected max overturn). The corresponding number of bins is [[math]\displaystyle{ n_{\text{rmax}} = r_{max} / r_0 }[/math]]
- Calculate the structure function [math]\displaystyle{ D_{ll} }[/math] for all possible bin separations [math]\displaystyle{ \delta }[/math] within [math]\displaystyle{ r_{max} }[/math] using either a bin-centred difference scheme or a forward-difference scheme.
- Perform a regression of [math]\displaystyle{ D_{ll}(n,\delta) }[/math] against [math]\displaystyle{ (\delta r_0)^{2/3} }[/math] for the appropriate range of bins and [math]\displaystyle{ \delta }[/math]r0 separation distances. Be aware of special considerations for forward-difference, center-difference schemes.
- Use the coefficient [math]\displaystyle{ a_1 }[/math] to calculate [math]\displaystyle{ \varepsilon }[/math] as
[math]\displaystyle{ \varepsilon = \left(\frac{a_1}{C_2}\right)^{2/3} }[/math]
where [math]\displaystyle{ C_2 }[/math] is an empirical constant, typically taken as 2.0 or 2.1.
Next step: Apply quality-control on dissipation rates (QA2)
Previous step: Apply quality-control on velocity time series data (QA1)
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