[Acoustics] GPS/ADCP questions

[Christopher A Curran]

Hello,

1)  We did some ADCP meas. recently with an Ag132 GPS that shows vertical 
banding in the WinRiver velocity magnitude contour plot when GGA is used 
as reference, but when Bottom Track is toggled as reference, the bands 
dissappear and the transects looks much cleaner. I was using a usb-serial 
adapter for GPS, a 5Hz position rate and a 9600 baud on the NEMA output. 
The transects were done in saltwater bay during a tidal change and were 
long,10-15 min. each. The GPS coordinates at start and finish agreed with 
a separate handheld unit. The compass calibration on the 1200KHz RioGrande 
was done correctly, but the unit is about 6 yrs old now. Any ideas what's 
causing that apparent velocity banding w/ GGA plot?

2) What's the best ADCP baud rate to use with GPS?

3) What's the best GPS baud rate into laptop (Ag132, output port A for 
NEMA, I think 38.4K is max for the unit)?

4) Do I want to use the fast output option, 10Hz position rate?

Thanks for your answers.

Chris Curran
U.S. Geological Survey
WA Water Science Center
Tacoma, WA 
(253) 428-3600  x2614
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