Processing your ADCP data using structure function techniques

To calculate the dissipation rate at a specific range bin and a specific time ensemble:

1. Extract or compute the along-beam bin center separation [$r_0$] based on the instrument geometry
2. Calculate the along-beam velocity fluctuation time-series in each bin $n$, where [Failed to parse (syntax error): {\displaystyle v’(n, t)} ] from the along-beam velocity data that has met the QC criteria (i.e. the data in Level 2 of the netcdf file)
3. Select the maximum distance ($r_{max}$) over which to compute the structure function based on conditions of the flow (e.g., expected max overturn). The corresponding number of bins is [$n_{\text{rmax}}=r_{max}/r_0$]
4. Calculate the structure function $D_{ll}$ for all possible bin separations $\delta$ using either a bin-centred difference scheme or a forward-difference scheme. Consider QA2 requirements when choosing differencing scheme.
5. Perform a regression of $D_{ll}(n,\delta )$ against $(\delta r_0{)}^{2/3}$ for the appropriate range of bins and $\delta$r₀ separation distances. Be aware of special considerations for forward-difference, center-difference schemes.
6. Use the coefficient $a_1$ to calculate $\epsilon$ as
   
   $\epsilon ={\left(\frac{a_1}{C_2}\right)}^{2/3}$
   
   where $C_2$ is an empirical constant, typically taken as 2.0 or 2.1.

Schematic showing along-beam distance $r$ and radial velocities.

Schematic showing the ADCP beam angles and the variables used to define the structure function Dll.

Next step: Apply quality-control on dissipation rates (QA2)

Previous step: Apply quality-control on velocity time series data (QA1)

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