[Acoustics] Question on Sontek SL beam vel's

[Victor A Levesque]

Hello Keith,

When you say you are looking at Beam 1 and Beam 2 velocities, do you mean 
you are looking at the x and y components of velocity (x being red and y 
being blue)? From your description, it does seem possible that the 
Argonaut has been rotated as Liz suggested.

Is the instrument located near or on a river bend...are the water levels 
much different this year than last year?
Are there nearby tributary inflows upstream of the SonTek?
Do the horizontally averaged velocities also differ from the previous 
installation or only the last two cells?
What frequency is the unit? How long is your sampling range? 
You state that only the last two cells of the multi-cell data seem to be 
affected...that may be  that the Argonaut is rotated in pitch or roll.
Are the noise level of the two instruments similar? Are the return signal 
strengths above the instrument noise.
Are the suspended solids concentrations different from one year to the 
next?
 I seem to have more questions than answers.

 If you want to discuss this, give me a call,


Victor Levesque

U.S. Geological Survey
Florida Science Center
St. Petersburg and Tampa, FL
727-803-8747 extension 3085
813-975-8620 extension 167





"Keith Ging" <Keith.Ging at lcra.org> 
Sent by: acoustics-bounces at simon.er.usgs.gov
08/30/2006 07:22 PM

To
<acoustics at simon.er.usgs.gov>
cc
Steven Clark <Steven.Clark at lcra.org>, Matthew Ables 
<Matthew.Ables at lcra.org>, Gene Taylor <gene.taylor at lcra.org>
Subject
[Acoustics] Question on Sontek SL beam vel's






I wanted to run this across everyone to see if my line of thought was near 
correct.  I've recently found that our rating has changed at one of our 
index-velocity sites based on 4 discharge measurements this year.  We 
cannot find any visual clues to suggest the channel or vegetation has 
changed.

After digging into the data through ViewArgonaut, I noticed two things 
that stood out.

1.    The multi-cell data shows the velocities of the last two cells are 
fluctuating more than usual at very slow vel's (<0.20 ft/sec) as compared 
to the previous 2 years (2004-2005).  However, the diagnostic data does 
not show anything in the path of the beams based on signal strength and 
SNR's.  Visual observations have found nothing in the channel to be 
different.

2.    I then looked at the beam velocity data and found the vel's of beam 
1 & 2 to roughly equal one another fairly consistently in 2004 (the 
magnitude is near the same but one is negative and one is positive).  This 
changed in 2005 and 2006.  Beam2 is about 0.10 ft/sec slower than Beam1 at 
the slower vel's.  Many times Beam2 is half of Beam1 vel's.  Could this 
indicate the SL has moved slightly?  The SL was replaced during the 
off-season between 2004 and 2005.  We do have it marked to prevent this 
from happening.  We also recently shot levels to make sure the SL had not 
changed in elevation which it had not.  I can only guess it may be turned 
slightly when it was replaced and we will be checking this soon.

Please let me know your thoughts.  I'm interested in how others have used 
the beam vel's to diagnose problems or any other parameter logged by the 
SL.

Thanks,

Keith Ging, P.G.,  Senior Hydrologist
River Operations
Lower Colorado River Authority
3505 Montopolis Dr,  Austin, TX  78744
Phone:  512-356-6009
Toll Free:  1-800-776-5272 ext. 6009
Fax:  512-356-6059
Email:  kging at lcra.org


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