YSI SonTek RiverSurveyor, System Manual

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SonTek/YSI Inc
RiverSurveyor System Manual (May 1, 2007)
69
The
Velocity Profile Extrapolation
dialog box (
Figure 5-7
) is
used to set up the two main processing requirements:
•
The Velocity Profile Calculation
•
The method of determining where the profile ends
Velocity Profile Calculation
First decide whether the top and bottom unmeasured areas
will be calculated using the same parameters or independ-
ently. Select either
Same Top and Bottom
or
Independent
Top and Bottom
in the
Velocity Profile Extrapolation
dialog
box (
Figure 5-7
).
•
If you chose
Same Top and Bottom
, only the
Top
un-
measured area controls will be available. Field entries
will be assumed to be the same for both the top and bot-
tom unmeasured areas.
•
If you chose
Independent Top and Bottom
, the controls
for input of parameters for the
Bottom
unmeasured area
will be enabled.
Calculation of velocities in the unmeasured areas can be
based on either of two methods:
•
Constant
– The average velocity of the number of cells
in
Use N cells
is applied to the unmeasured area.
•
Power Fit
– Use the power-fit equation (
Equation 5-1
) to
compute the velocities in the unmeasured areas. The
constant
b is set to 1/6 (i.e., 0.166667) by default. A
range of cells (instead of the entire profile) can be used
in the calculation. This is of particular importance in the
case of stratified flows (§
4.3.4
) where only a select
number of the adjacent cells would be representative of
the velocities in the unmeasured area.
Determining the end of the profile
Water current velocities measured near the bottom can be contaminated by bottom reflections or
potential side-lobe interference (i.e., “bad” cells). Even though the ADP may have measured ve-
locities in these bottom cells, this data should be discarded, and the velocities in this area will
need to be computed based on the uncontaminated (“good”) cells.
There are two options for removing these “bad” cells closest to the bottom:
•
Discard last N cells
– Use this method to always discard the last N cells from every profile.
Be careful when using this technique with values of N greater than 1. If the profile only has
N cells or less, the entire profile will be discarded.
•
Discard last N % of the profile
– This is the default method for removal of “bad” cells from
the profile. A minimum of one cell will always be removed from the end of the profile. The
default is 10%.
Figure 5-7. Velocity Profile Extrapola-
tion dialog box