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b) The standard FlowTracker2 uses a 2D side-looking probe. The sampling volume
is located 10 cm (4 in) to the side of the probe, and can operate in as little as 2
cm (1 in) of water.
c) To work in both shallow and deeper water, a combination 2D/3D side-looking
probe is available. This has a sampling volume located 10 cm (4 in) to the side of
the probe, and can operate in as little as 2 cm (1 in) of water. It measures 2D
velocity in shallow water (with only two arms submerged), and 3D velocity in
deeper water (with all three arms submerged).
13.10. Sound Speed
The FlowTracker2 uses sound speed to compute velocity from the measured Doppler
shift, and to precisely determine the location of the sampling volume.
13.10.1
Sound Speed Function
The speed of sound in water is primarily a function of temperature and salinity.
a) Temperatures change of 5°C (9°F) results in a sound speed change of ≈1%.
b) A salinity change of 12 results in a change in sound speed of ≈1%.
c) A 1% error in sound speed results in a ≈2% error in velocity data.
13.10.2
Compensate for Changes
To compensate for changing sound speed, the FlowTracker2 does the following.
a) The FlowTracker2 includes a temperature sensor for automatic sound speed
corrections. Resolution is ±0.01°C (±0.02°F).
b) A user-input value of salinity is used for sound speed calculations.
c) If accurate salinity data has been specified by the user (±2), sound speed
changes can be assumed to have no impact on velocity data.
13.10.3
Environmental Conditions
Doppler current meters, such as the FlowTracker2, do not measure movement of water,
but actually the movement of particles in the water,
FlowTracker2 User's Manual (January 2019)
Figure 13:5 - FlowTracker2 Probe Configuration
SonTek – a Xylem brand
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