SonTek/YSI Argonaut-XR Technical Manual - HydroScientific West

SonTek/YSI
Any large objects within the measurement field will show up as spikes in the return signal; these
spikes may be present in one or more beams. If any spikes are present in some portion of the
measurement volume, velocity data will be contaminated to some degree. The acoustic return
signal for each sample is highly variable; it is useful to store a number of pings to an output file
and look at the mean profile to look for any consistent source of interference.
When working near underwater structures or deployment lines, interference can come from direct
reflections and from flow distortion caused by the object. To the greatest extent possible, place
the Argonaut measurement volume in an open water area free from sources of acoustic or flow
interference.
Measurement volume limits
In open water, the maximum effective range for the Argonaut XR and SL is determined by the
distance at which the signal strength approaches the noise level. For most environments, the
signal strength will be above the noise level out to the maximum allowed range of 15 m. In clear
water, signal strength may approach the noise level before reaching 15 m. This can be seen
clearly from the output of ARGCHECK. Capturing a number of pings using the output file option,
and plotting the mean signal strength versus range lets you directly measure the maximum range.
During operation, the Argonaut XR and SL will automatically end the measurement volume if
the signal level is less than six counts higher than the noise level. This is to prevent
contamination if signal strength levels are not sufficient. For example, if the end of the
measurement volume is set to 15 m, but signal strength is only sufficient to a range of 13 m, the
system will automatically end the measurement volume at 13 m. The precise start and end of the
measurement volume is reported with each sample.
When working near boundaries or underwater structures, the limits of the measurement volume
are set by the range at which the system sees the reflection from the boundary. This is illustrated
in Figure 17. You must set the measurement volume limits to avoid any contamination from the
boundary reflection. The only exception to this is when using the Argonaut XR up-looking with
dynamic boundary adjustment – see the Argonaut Operation Manual for details.
The end of the measurement volume should be placed no closer than the greater of 0.25 m and
10% of the total range to the boundary. For the example in Figure 17, the boundary is at a range
of 6 m; the end of the measurement volume should be at least 0.6 m (10% of 6 m) from the
boundary. Thus, the end of the cell should be placed at 5.4 m or less. If there is any variation in
boundary range or instrument mounting, the end of the measurement volume should be placed to
avoid interference at all times.
7.3. System Diagnostics
When looking at the output data, there are four basic features to verify system operation: signal
strength profile, noise level, boundary reflections, and sine/cosine data.
Signal strength profile
When looking at the signal strength profile, data from all active beams should be similar in
magnitude and shape. Note that the Argonaut SL has only two beams; the third beam is still
plotted but will show a constant signal strength at the noise level. Each beam should see initial
signal strength of roughly the same magnitude and should decay at the same rate. Check that all
beams have an unobstructed view and are not showing spikes from objects in their path.
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Argonaut Software Manual (March 1, 2001)