SonTek RS5 User Manual (August 2020) 77
7.5.5.10 Track Reference
The ADP measures water velocity using multiple acoustic pulses transmitted and received
throughout the water column (see RS5 Technical Manual for more details, coming soon). When
the ADP is in motion, the apparent velocity measured by the ADP is a combination of boat
velocity and water velocity. In order to determine true water velocity the boat speed must be
determined and then subtracted from the apparent velocity. The RS5 moving boat application
offers four methods, known as tracking references, to determine boat velocity.
Figure 54. Track Reference Options
An appropriate track reference should be selected when setting up a measurement, but
can be changed during post-processing, if necessary.
1. System
The ADP references velocity data only to itself. This option should only be used in
specialized applications by experienced users. It is not recommended for discharge
measurements from a moving vessel.
2. Bottom Tracking (Default)
Boat velocity is calculated using signals received from multiple acoustic pulses reflected
from the channel bed and banks. If the channel bed is stationary (i.e. no bedload flux),
then the apparent velocity will consist entirely of boat and water motion, so water
velocity can be determined by removing bottom-tracked boat motion. If the channel bed
is in motion (i.e, active bedload flux) the apparent velocity will involve a combination of
boat, water, and channel-bed velocities. In this case, the user can proceed in one of two
ways: (1) use a moving-bed test to measure and correct for the effects of bed motion on
the bottom tracking (loop or SMBA, discussed in Sections 7.10.1 and 7.10.2), or (2) use
GPS/GNSS to measure the boat track. Bottom tracking is the only reference available
for the RS5 Basic model.
As a general note, users can also opt to use a third option of taking a measurement in
Stationary mode (coming soon).
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