Using a Velocimeter 55
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volume).
When mounting your Vectrino or the Vectrino Profiler, use the recessions to strap it to the
structure. Never use the probe stem as mounting point.
Consider the effects of large objects on the flow itself. A rough rule of thumb is that objects disturb
the flow as far as 10 diameters away from the object. Flow disturbance is greatest directly
downstream in the wake behind the object.
All acoustic transducers must be submerged during data collection. Operating your sensor when
the transducers are out of water will not cause any damage, but your data will be meaningless.
For side-looking probes, it is possible to collect 2D-data with only the lower receiver arms
submerged.
Make sure your mounting structure is stable. Small vibrations in the mount can generate large
accelerations in the data.
The best quality is achieved if the main flow direction is perpendicular to the transmit axis. Flow
directly into the transmit axis should be avoided.
To align the Vectrino or Vectrino Profiler in a laboratory flume to ensure alignment of the
coordinate system, here are some tips:
o For a quick setup aligning everything by eye works surprisingly well if you have good references
to align against (flume walls are great for this).
o For a more rigorous setup a post level (two spirit levels mounted orthogonal to one another) can
be used to make sure the mounting fixture and probe are level. This assumes the top of your
flume is level since everything is usually mounted on a cross piece to it. If you have a tilting
flume this method will not work.
o For a non-standard setup where the probe is horizontal instead of vertical or for side looking
probes, a level of any type is needed to make sure the probe head parallel to the flume bottom
or very accurate distance measurements.
o Look at the probe check plot after mounting the probe and filling the flume with water. Tilts in the
head can be identified there based on the return echo from the bottom (as long as the
velocimeter can see the bottom). For example, look at the sharp front of the bottom echo and
just make sure all the beams see it in the same location.
o As far as rotation of the head, if you have a ruler with a wide enough surface, we use a level with
markings on it's top, you can align the upstream and downstream probe pair at the same
distance from one wall. It's also fairly easy to rotate the head once the flume is running and try
to minimize the cross stream and vertical components (if this is how your flow is working).
o For example, use zipties to mount the probe head as they will typically allow easier adjustment
and are difficult to overtighten and cause damage to the probe head.
o If you do not mind transforming your data, you can develop a minimization routine that will rotate
and apply pitchs and rolls to the measured velocities to "level" the head by minimizing the
appropriate components
2.5.5 Wave Measurements
This section is written with Vectors in mind. Before describing each setup parameter for waves, there
are a couple of things to be aware of:
Keep in mind that the location of the pressure sensor is located where the stem is connected to
the unit. This is the location from which one measures the distance off the bottom. It is later
entered as a parameter for the wave processing.
Special consideration must be taken when using a Vector with a cabled transducer array (opposed
to the firmly attached stem type). For the cabled type, it is critical that during deployment the
instrument’s array relative to its body (cylinder) is the same as it is with the Vector with the stem.
This is because the internal tilt sensor determines up or down, and ultimately ensures that the
correct coordinate system is used for the directional estimates.
For more information about waves and wave measurements for the Vector, it is recommended to
take a look in this section: Measuring Waves. More details about wave processing can also be found
in the manual called Comprehensive Manual - ADCP (available in the web site).
Burst Sampling vs Continuous Sampling: Wave data is collected in a mode that is referred to as
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