Comprehensive Manual108
© 2018 Nortek AS
It is also a good routine to pay attention to the Memory required review in the right side of the
deployment planning dialog.
5.3 Suspicious Data
If your data does not look right, the first step should be to check how the instrument was deployed/
mounted.
For the Vector: Inspect the Pitch, Roll and Heading data, in addition to pressure. This will in an
efficient way tell you how the instrument has behaved during deployment, and, most importantly,
indicate whether the data are trustworthy or not. For more about this, check out the interesting
Quality Assurance section.
5.3.1 Signal Strength
The instrument cannot measure velocity accurately if the water has too few scatterers. The data
quality will be questionable when signal levels are down around the noise level, a rule of thumb is
that the signal should be at least 6dB higher than the noise floor. When using the instrument in high
latitude areas or really deep waters the purity of the water can affect the signal strength and thus
also quality of the measurements. The low presence of scattering particles in the water cause
extremely low reflected signal level. The Probe Check is an invaluable tool if there is doubt about
signal strength.
5.3.2 Diagnostic Testing Using the Probe Check Function
The figures below shows Probe Check displays resulting from different problems. If you need a
reminder on how to interpret a probe check, take a look at this section: Probe Check. These probe
checks are from a Vectrino, but the same effects are in most cases valid for the Vectrino Profiler and
the Vector as well. If there are any exceptions, it will be mentioned. It is recommended to look at the
probe checks presented both as amplitude and SNR.
Below is a presentation of the most common problems together with our suggestions on how to
improve the result of the check, if it is not related to a damaged probe. For the troubleshooting to be
extra effective, a "before" probe check to compare your suspicious probe check against is a good
starting point. If you have older data files with good scattering conditions this should come in handy.
Boundary interference: The sample volume should be centered around 50 mm. Suggestion: Try
using a deeper bucket.
Multiple echos from the bottom reflecting off the surface can also appear in the probe check data.
These will typically be at roughly integer multiples of the actual distance to the bottom. Depending
on the acoustic path length, an echo closer to the actual boundary position may be the result.
When a side-looking Vectrino probe is placed close to the bottom, the two receivers slanted 45
degrees may see interference from the bottom. If you see interference in beam 3 and beam 4, try
moving the probe a bit up in the water column.
To Next Page
Loading...
