Xylem SonTek FlowTracker2 - Signal to Noise Ratio (SNR)

SonTek – a Xylem brand
FlowTracker2 User’s Manual (January 2019)
84
Parameter
Description
Expected
• Large angles may be unavoidable at some sites.
Tilt Angle
Angle of the wading rod relative to the vertical,
• Used for both discharge and general mode,
• A good measurement should have small tilt angles,
• Large tilt angles may be unavoidable at some sites.
Ideally < 5º
Station
Percent
Discharge
%Q is the percentage of the total discharge in a
single measurement station,
• Most agencies have criteria for the maximum %Q.
Typical criteria:
Ideally < 5%
Maximum < 10%
Station
Water Depth
Depth
is the maximum percentage variation in depth
between adjacent stations.
Typical criteria:
Maximum < 50%
Station
Location
Location is the maximum percentage variation in
location between adjacent stations.
Typical criteria:
Maximum <
100%
Velocity
Profile
0.2 \ 0.8
0.2 \ 0.8 Velocity Profile evaluated against expected
velocity distribution,
• Used for discharge measurements only,
• Suggest 0.6 depth measurement if set criteria is
complied with.
Ideally: near-
surface velocity >
n Velocity
Signal to Noise Ratio (SNR) 6.1.1
Signal to Noise Ratio (SNR) is a measure of the strength of the reflected acoustic
signal relative to the ambient noise level of the FlowTracker2. SNR is the most important
quality control data provided by the FlowTracker2.
a) SNR is reported in logarithmic units (dB). It is recorded with each one-second
velocity sample.
b) For the best operating conditions, SNR should be greater than 10 dB.
c) The FlowTracker2 can operate reliably with SNR as low as 4 dB, although the
noise in individual measurements will increase.
d) Low SNR indicates a lack of suspended material in the water. For clear water,
seeding material can be introduced to increase SNR. Seeding is typically only
required in large laboratory tanks. Most field applications have sufficient natural
scattering material.
SNR
Data
Display
e) The SNR data displayed during and after a point velocity measurement and
when a station and or stations are completed in both General and Discharge
Modes are supplied in Table 6:2. Individual beam SNR data can be accessed by
exporting the raw data in either JSON or CSV format from FlowTracker2 desktop