Bottom Check
In addition to velocity measurements, the backscatter signal can be used to
determine the instrument elevation above the bottom. A high intensity echo is
produced when the transmit pulse hits the bottom. The central transducer of the
Vectrino Profiler includes a transmit/receive switch allowing profiles over the full
elevation range of the instrument to be collected. The bottom check feature
collects a profile over a selected range and finds the maximum peak within this
range. A quadratic fit to the peak is used to determine the associated distance
to the bottom. Bottom check data is interleaved with the velocity data and can
be sampled at a rate of up to 10 Hz (dependent upon velocity sampling rate).
The bottom check simplifies the data analyses by allowing all the velocity data
points to be referenced to the bottom position. It is very important to adjust the
Gain Reduction
option such that the return signal strength is below
approximately -10 dB to get accurate bottom measurements (see software
manual for more information).
Mounting Guidelines
Make sure that there are no obstructions between the sensor and the focal
point (sampling volume) located about 5 cm from the center transducer.
The sensor is a pulse coherent system which means it is susceptible to
pulse interference when measuring near boundaries. This interference is
called “Weak spot” and should be avoided. More information about this can
be found in the Comprehensive Manual
– where a table presenting the
distances where weak spots can occur can be found.
Consider the effects of large objects on the flow itself. The flow disturbance
is greatest directly downstream in the wake behind the object.
All acoustic transducers must be submerged during data collection.
Operating the Vectrino when the transducers are out of water will not cause
any damage. For side-looking probes; it is possible to collect 2D data with
only the lower receiver arms (and center transducer) submerged.
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.
Make sure your mounting structure is stable. Small vibrations in the
mounting can generate large accelerations in the data.
The sensor is not designed to be used in saline environments, and using it
outside lab may cause corrosion on the probe. If used in saline waters,
make sure to use it for only short periods and clean it properly with fresh
water after the measurements are done.
Note: When mounting; use the grooves to strap the sensor to the structure.
Never use the probe stem as mounting point.
Proper mounting of the sensor is crucial for collecting quality data. Read more
about this in the Mounting Guideline.
Seeding
In order to measure water velocities, the sound waves emitted by the center
transducer must be reflected by scattering material suspended in the water. The
velocity that is measured is consequently the velocity of the water, assuming
the particles move with the same average speed as the surrounding water. If
the instrument is to be used in a laboratory environment, one will need to add
seeding. If you are unsure about the amount of particles to add, please check
the Manual or contact us for further guidance.
Basic Principles
The Vectrino Profiler profiles
the sampling olume over a
30 mm range and provides
three-component velocity
observations with a
resolution as fine as 1 mm,
and with a sampling rate as
high as 100 Hz. The
Vectrino Profiler can
measure the distance to the
bottom at rates of up to 10
Hz by interleaving bottom
detection pings and velocity
profiling pings. The Vectrino
Profiler use separate
transducers to transmit and
receive the acoustic signal,
and is thus a so-called bi-
static sensor.
Software
New software provides
enhanced capabilities such
as real-time plots of velocity
profiles, velocity standard
deviation, energy spectra
and color contour plots. The
acquisition software is used
to configure the instrument
and to collect, save and
display data in real time.
Proper visualization of data
as it is being collected
greatly facilitates the
operation of the instrument,
allowing early detection of
incorrect configuration
parameters or anomalous
behavior of the instrument
due to external factors.
The software is also
capable of supporting
multiple instruments
simultaneously. Each
instrument is provided with
its own panel created in a
separate tab.
