Tow Tank Testing with FlowTracker Handheld ADV

January, 2001 - SonTek's FlowTracker Handheld ADV (Acoustic Doppler Velocimeter) was tested at the U.S. Geological Survey (USGS) tow tank at Stennis Space Center, Mississippi. SonTek ADVs have been well established for many years as the preferred sensor for high-resolution 3D velocity measurements. The FlowTracker (Figure 1) provides ADV performance from a simple keypad/LCD interface that allows rapid data collection in any environment (no PC required). The purpose of these tests was to evaluate the accuracy of velocity measured by the FlowTracker ADV against the speed of the tow cart.

The USGS tow tank (Figure 2) is 450 feet long, 12 feet wide, and and 12 feet deep. For this test, cart speeds from 0.1 to 5.0 ft/s were used. The FlowTracker ADV was mounted from a pole in the center of the cart at a depth of 12 inches, and data were collected with the probe rotated at several different angles (to ±40°) into and away from the flow.

Figure 3 shows FlowTracker ADV current speed vs. cart speed for runs perpendicular and 10° off perpendicular to the flow. A regression of all runs in Figure 3 gives a slope of 0.99 and an offset of 0.009 ft/s. This is well within the accuracy specifications of the ADV (<1%) as well as expected uncertainties due to residual currents in the tank (±0.01 ft/s).

The FlowTracker ADV's time response was also tested. Since the ADV records velocity data once per second (and each 1-second sample is completely independent), it is interesting to look at this data to determine the time required for the ADV to make an accurate measurement of velocity. Figure 4 shows the ADV velocity data for one run, with results typical for data at all cart speeds. In this run, the ADV mean velocity was 2.203 ft/s (difference of 0.7% from cart speed); the standard deviation of 1-second velocity data was 0.018 ft/s (0.8% of cart speed).

This demonstrates that the FlowTracker ADV can offer excellent performance for observing real variations in water flow on a 1-second time scale (accuracy is 1% of measured velocity for each 1-second sample). For the mean water velocity at a given location, the averaging time required will be strictly a function of the real variations in the flow. Uncertainty in the ADV velocity will have no significant impact.

The results of this test show that the FlowTracker ADV can offer excellent performance in measuring water velocity at various speeds and also on small time scales. For a full copy of the report, please contact SonTek.

Note: The results shown here, while made using USGS facilities and with support from the USGS, are presented by SonTek and do not imply any endorsement of this product by the USGS.

• FlowTracker Handheld ADV

For information about the USGS policy on FlowTracker discharge measurements:

• The following link is to a Technical Memorandum issued by the U.S. Geological Survey's Office of Surface Water. This memorandum [pdf format] describes the USGS policy on the use of the FlowTracker for discharge measurements. The information presented in this memorandum is a courtesy from the USGS, and should not be construed as an endorsement. Additionally, this memorandum is provided "as-is"; that is, the USGS does not provide support for this memorandum outside its own agency.
  http://hydroacoustics.usgs.gov/memos/OSW2004-04.pdf