Xylem SonTek FlowTracker2, User Manual

Page: 97 / 308

SonTek – a Xylem brand
FlowTracker2 User’s Manual (January 2019)
96
Velocity Profile 0.2 \ 0.8 6.1.10
The Velocity Profile 0.2 \ 0.8 criterion is intended to identify unusual velocity distribution
within the measurement profile. .
a) For an ideal discharge measurement site, the velocity distribution in the
measurement profile should follow 1/6 power-law.
Velocity
Profile
Evaluate
b) The velocity measurements performed at 0.2 time depth and 0.8 time depth are
evaluated against expected velocity profile. If any of the following conditions are
true, this indicates an unusual velocity profile, and the user is given the option to
add a third velocity measurement at 0.6 time depth.
i). The magnitude of the near-surface velocity (0.2 times depth) is less than the
magnitude of the near-bottom velocity (0.8 times depth).
ii). The magnitude of the near-surface velocity (0.2 times depth) is more than two
times the magnitude of the near-bottom velocity (0.8 times depth).
iii). The near-surface velocity (0.2 times depth) and near-bottom velocity (0.8
times depth) show flow in the opposite direction.
6.2. Quality Control Warning Messages
Types of Warning Messages 6.2.1
Quality Control Warning Message is supplied when measured variable exceeds the
expected criteria of each parameter in Quality Control Parameters . The quality control
warning messages implemented in the Quality Control process are supplied in Table 6:4.
The table layout describing the quality control warning messages consist of the following
key components,
a) Warning , the warning supplied when the parameter is exceeded,
b) Reporting , aspect of the measurement process relate to the quality control
warning message,
c) QC Criteria , quality control criteria based on SonTek default values or user
specified.
Table 6-4 - Quality Control Warning Messages
Warning Reporting QC Criteria Description Suggested Action
Low SNR
Point
Velocity
Low SNR SNR below 4 dB
•
Improve SNR
Approach
Low SNR
Point
Velocity
Approach
Low SNR
SNR between 4db and 7 dB
•
Improve SNR
Beam SNRs
Not Similar
Point
Velocity
SNR
Threshold
Difference in SNR for any 2
beams is >
SNR Threshold .
•
Look for underwater
obstacles; repeat
measurement.
•
Check probe operation
Large SNR
Variation
Point
Velocity
SNR
Variation
One-second SNR data varies
more than expected during a
measurement. May indicate
underwater interference or a
•
Look for underwater
obstacles; repeat
measurement.
•
Look for environmental