Processing your ADCP data using structure function techniques

Structure Function Processing Steps

1. Extract or compute the along-beam distance of the center of each bin [zb] and bin center separation [r0]
2. Calculate the along-beam velocity fluctuations in each bin [v’(zb)]
   1. If using burst sampling, calculations are done over the length of the burst if stationary
   2. If using continuous sampling, a time interval must be selected in which the flow can assumed to be stationary
   3. You can calculate the fluctuations around:
      1. The mean of the time interval
      2. A linear detrend of the time interval
      3. A low pass filtered signal
3. Select the maximum distance over which to compute the structure function based on conditions of the flow (e.g., expected max overturn) [rmax]
4. Start at the first bin where zb >= rmax/2
5. Compute the centered difference of v’ along the beam for the first pair of bins on either side: v’(z+r0)-v’(z-r0)
6. Compute the second order structure function D(z,r) = mean-square of the velocity fluctuation difference: D(z,2*r0) = mean(v’(z+r0)-v’(z-r0))2
7. Repeat steps 5-6 for all pairs of bins where the separation distance between bins r <= rmax
8. With these data points, fit a line to the form D(z,r) = N + Ar2/3 to estimate values for A and N where A = Cv2e2/3 and N is an estimate of the uncertainty due to noise.
9. Solve for e using Cv2 = 2.1
10. Repeat the steps in (5) – (9) for each bin until zb + rmax/2 >= end of profile