Xylem SonTek River Surveyor M9, Системное руководство

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SonTek, a Xylem brand
26 RiverSurveyor S5/M9 System Manual (February 2013)
The Transect component can be further broken up into the Top Estimate, Middle or Measured
Area and Bottom Estimate as shown in Figure 22 below:
Figure 22. Cross-Sectional Areas Not Measured by the ADP
Therefore the Total Discharge can be calculated by summing the Start Edge, Top Estimate,
Measured Area, Bottom Estimate and End Edge. Only the Measured Area is measured by the
acoustic Doppler profiler. It is important to note that all other areas are estimated using industry
recommended and approved calculations.
The reasons for breaking up the total discharge calculation into several components are due to
limitations inherent in all acoustic Doppler profilers. An acoustic Doppler profiler cannot meas-
ure the entire river cross-section due to several issues:
•
There is a minimum operating depth for the profiler. At depths lower than this minimum,
the water velocity and therefore the discharge must be estimated based on the velocity
and depth measurements on the edges. The Start and End Edges are measured in this
way.
•
The mounting depth plus a short distance (referred to as the blanking distance) from the
profiler to the start of the measured velocity profile leave a section of the water at the
surface unmeasured. This area is referred to as the Top Estimate.
•
Potential data contamination in the last cell (i.e., the cell is partially or fully “touching” the
riverbed), or potential side-lobe interference at the end of the profile, leaves a section of
water at the bottom unmeasured. This area is referred to as the Bottom Estimate.
So, how do we calculate the velocities and discharges in each of these estimated and edge ar-
eas?
A technique known as Velocity Profile Extrapolation is used to estimate the unmeasured areas
at the top and bottom. This theoretical approach to modeling of the velocities within the water
column allows all velocities and therefore the discharge to be computed.