Case Study of Precision of GPS Differential Correction Strategies: Influence on aDcp Velocity and Discharge Estimates
Publication: Journal of Hydraulic Engineering
Volume 132, Issue 3
Abstract
The precision of four differential global positioning systems (DGPS) was evaluated in the context of fluvial water velocity and discharge measurement. DGPS is used to resolve water velocities measured with an acoustic Doppler current profiler (aDcp) into earth coordinates if bottom tracking is unavailable. The DGPS systems assessed were: (1) the dual frequency real time kinematic (RTKL1L2); (2) the single frequency real time kinematic (RTKL1); (3) the code-phase Canadian Coast Guard (CG); and (4) the code-phase Wide Area Augmentation System (WAAS). Repeat discharge surveys were conducted at a transect of the Gatineau River, Canada, simultaneously collecting bottom track boat velocity and boat velocity from all four DGPS . The mean absolute single ping differences between and were 3.1 (RTKL1L2), 3.2 (RTKL1), 8.9 (CG), and (WAAS). Errors were observed more often near channel margins, presumably due to obstruction and multipath associated with riverbank vegetation and buildings. DGPS velocity errors were random, and a large number of DGPS positions were utilized across the section to record discharge. Accordingly, errors in discharge were relatively small, with maximum percentage differences between single transect and of 0.9 (RTKL1L2), 1.0 (RTKL1), 2.4 (CG), and 3.1% (WAAS). Simulations suggest large discharge errors (up to 51%) are possible under low sampling intensity (20 pings) and small channel velocity relative to average error (ratio of 1).
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Acknowledgments
We wish to thank Paul-Emile Bergeron, Brian Pessah, Murray Jones, and Adam Dowler at Water Survey of Canada for their technical support during the gathering of data required for this study. At RDI, many thanks to Alicja Pulawska for her help in understanding the computations performed by WinRiver. Please note that the use of trade, product, or firm names in this paper is for descriptive purposes only and does not imply endorsement by Water Survey of Canada or the Canadian government.
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 132 • Issue 3 • March 2006
Pages: 225 - 234
Copyright
© 2006 ASCE.
History
Received: Aug 2, 2004
Accepted: Apr 22, 2005
Published online: Mar 1, 2006
Published in print: Mar 2006
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