[Acoustics] mode use for slow vel

[rwellman]

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>
> Sent by: acoustics-bounces at simon.er.usgs.gov
>
> 09/13/2006 11:50 AM
>
> 	
> To
> 	acoustics at simon.er.usgs.gov
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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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