[Acoustics] mode use for slow vel

[Kellman, Orlin]

You need to be a smooth operator when performing your transects.


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	From: acoustics-bounces at simon.er.usgs.gov
[mailto:acoustics-bounces at simon.er.usgs.gov] On Behalf Of rwellman
	Sent: Friday, September 15, 2006 10:52 AM
	To: James J Duncker
	Cc: acoustics at simon.er.usgs.gov
	Subject: Re: [Acoustics] mode use for slow vel
	
	
	Dave,
	Jim mentioned some of the problems that can arise when making
measurements in extreme low velocity conditions. Wind conditions should
be measured and documented, it doesn't take much consistent  wind to
push surface flows opposite of mean flows-leading to poor estimates in
the surface unmeasured zone. Edge estimates can be problematic, be
prepared to end the transect a little further out than you normally
would and measure your edges with a current with a AA or pygmy (verify
your edge distances) If possible - use a tagline to move the boat or a
'clotheline' cableway for the pontoon, without such you'll have a @#$%
of a time maintaining a slow constant speed that doesn't exceed your
water velocities. SLOW and SLOWER is the name of the game.
	
	Roy Wellman
	USGS, Portland, Or
	
========================================================================
================ 
	
	James J Duncker wrote:
	


		Dave; 
		As others have mentioned, mode 5 should work, but at
really low velocity situations, are you sure you have steady flow?
We've found that a lot of factors (boat speed, edge estimates, variable
wind speed, upstream and downstream controlling works, etc) can
influence the flow in low velocity settings to make it difficult to get
"repeatable transects". 
		
		Jim 
		  
		James J. Duncker
		Hydrologist
		U.S. Geological Survey 
		
		
		
David M Hernandez <dmhernan at usgs.gov> <mailto:dmhernan at usgs.gov>  
Sent by: acoustics-bounces at simon.er.usgs.gov 

09/13/2006 11:50 AM 

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Subject
[Acoustics] mode use for slow vel	


	
	




		
		To all, The conditions are: Channel width 100 to 200 ft.
Depth 3 to 7 ft. velocity < .1ft/sec. Used Rio 1200khz water mode 12sb
bottom mode 5. Not sure it was the best combination for those
conditions, does anyone have similar conditions? Which mode combinations
would work best for collecting repeatable transects?
		Dave_______________________________________________
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