[Acoustics] Sontek SL coordinate systems

[John M Shelton]

FYI
As many of you are already aware, the Sontek SL can output data in two
different formats, XYZ and Beam.  By default the XYZ coordinate system is
used.  The majority of USGS users are using X velocities for the
computation of index velocity records.  If the Beam coordinate system is
used, velocity data is output as "along-beam" velocities or those
velocities directly toward of away from the transducer.

We recently replaced an SL and the data from the new unit followed the
expected trend, but the magnitudes were considerably lower than expected
(see attached plot). We were finally able to figure out that the coordinate
system had been set to "beam."  Changing back to XYZ is a single command
(coordsystem xyz), but it is not a command we routinely look at when
deploying the SL.

The coordinate command could have been changed inadvertently, or another
possible explanation is the use of older versions of the Sontek software.
When users run a beam check or argcheck, the coordinate system is changed
to "beam."   When the beam check is completed, the software is supposed to
change the coordinate system back to "xyz."  Some older versions of the
software sometimes failed to change the coordinate system back.  The latest
recommended software versions are available from the Hydroacoustics web
page (http://hydroacoustics.usgs.gov/equipment/software/index.html) or from
Sontek.
(Embedded image moved to file: pic26500.pcx)
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John M. Shelton
Hydrologist
U.S. Geological Survey
Florida Integrated Science Center
Center for Aquatic Resource Studies
224 West Central Parkway, Suite 1006
Altamonte Springs, FL 32714
P 407-865-6725 x151
F 407-865-6733
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