[Acoustics] Use of Filters in DGPS

[Kevin Oberg]

This Hydroacoustic Update describes a problem that has been 
identified regarding the use of differential global positioning 
systems (DGPS) receivers with ADCPs, and provides information about 
how to correct this problem.

USGS users (and others) often use DGPS receivers in conjunction with 
ADCPs.  DGPS receivers may be used with ADCPs when the boat velocity 
measured using bottom tracking is not accurate (moving bed condition) 
or when mapping velocity vectors in a river, lake, or estuary.

Many of the DGPS receivers used in the USGS are Trimble AgGPS 132[1] 
receivers, although other models and manufacturers are also in 
use.  During the past 6-9 months, OSW personnel have found numerous 
instances in which the PV Filter in AgGPS 132's was not 
disabled.  Based on information available to the OSW at present, it 
appears that discharges measured using DGPS receivers with the PV 
filter enabled were not significantly compromised.  Nevertheless, 
position data for individual velocity measurements obtained using 
DGPS receivers with the PV filter enabled are likely to be in error.

If you have any questions, please contact Kevin 
Oberg(kaoberg at usgs.gov or 217-344-0037) or email the USGS Hydroacoustics
Work Group, hawg at simon.er.usgs.gov.

This Hydroacoustic Update can also be accessed at:
http://hydroacoustics.usgs.gov/applications/HydroacousticsUpdate-PVFilter.pdf



[1] The use of trade, product, or firm names in this document is for 
descriptive purposes only and does not imply endorsement by the U.S. 
Government.



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Kevin Oberg
USGS - Office of Surface Water
Voice:  217.344.0037 extension 3004
Cell:   217.840.9739
http://hydroacoustics.usgs.gov/