Moving-Boat Deployments — Guidance
The USGS has developed guidance to help ensure that data collected by USGS personnel are consistent and of high quality. The guidance consists of policy specified in technical memorandums (and referenced reports) and other best practices that are provided in published reports, papers, hydroacoustic updates, and information provided on this web site.
Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat, Version 2, December 2013 by David S. Mueller, Chad R. Wagner,
Michael S. Rehmel, Kevin A. Oberg, and Francois Rainville. Published as U.S. Geological Survey Techniques and Methods 3A-22, 2009.
Limitations of the Loop Method. The OSW has documented a limitation of the loop moving-bed test for streams that are wider than 180 ft, caused by the combined effect of potential heading errors, stream width, and test duration. No change in OSW policy is introduced; rather the limitations of the loop method are more clearly explained.
Quality-Assurance Plan for Discharge Measurements Using Acoustic Doppler Current Profilers (Oberg, K.A., Morlock, S.E., and Caldwell, W.S., 2005, U.S. Geological Survey Scientific Investigations Report 2005-5183.)
Guidance on the use of the Loop Method and release of "Application of the Loop Method for Correcting Acoustic Doppler Current Profiler Discharge Measurements Biased by Sediment Transport." (OSW Tech Memo 2006.04) || [PDF Version]
Application of the Loop Method for Correcting Acoustic Doppler Current Profiler Discharge Measurements Biased by Sediment Transport by David S. Mueller and Chad R. Wagner. Published as U.S. Geological Survey Scientific Investigations Report 2006-5079.
Other Best PracticesCompass Calibrations
The compass calibration procedures and algorithms for the Teledyne RD Instruments (TRDI) RiverRay with Honeywell compass (original RiverRays, prior to vertical beam) and the SonTek RiverSurveyor M9/S5 with the 2nd generation compass (shipped prior to October 2014) have been shown to be unreliable in creating consistently accurate compass calibrations. These problems have been identified by the USGS through routine ADCP use and through specific testing.
TRDI replaced the Honeywell compass with an internally developed compass (ISM) in June 2012. All USGS RiverRays purchased prior to June 2012 should have had their RiverRay upgraded to the ISM compass.
SonTek developed a 3rd generation compass to address the problems the USGS identified with the 2nd generation compass. SonTek provides a free upgrade to the 3rd generation compass (OSW Informational and Technical Note 2014.27) for all USGS owned M9 and S5 ADCPs.
The following Best Practices are for RiverRays and RiverSurveyors with older compasses only.
Best Practice for Calibrating RiverRay ADCPs equipped with a Honeywell Compas (2009-2012). Document prepared August 2012.
Best Practice for Calibrating RiverSurveyor M9/S5 ADCP equipped with an 2nd Generation Compass (2008-2014). Document prepared August 2012.
Where compass accuracy is questionable, the use of the stationary moving-bed test will be consistently more accurate than the loop test and is recommended as the preferred moving-bed test for RiverRays and RiverSurveyors with older compasses or in any location where magnetic interference renders the compass inaccurate.
A webinar on SonTek RiverSurveyor compass issues, the 3rd generation compass, and use of the 3rd generation compass is available here.
Instrument Updates: It is always recommended that instruments used the latest approved Firmware and that data be collected and processed with the latest approved Software.
ADCP Check Measurements The USGS Quality-Assurance Plan for Discharge Measurements suggests that an annual instrument check be performed (see p. 24). Several offices have adopted this quality assurance practice. An excellent example of this kind of test was completed by the USGS California Water Science Center. Their internal report, titled Summary of 2007 California District ADCP Check Measurements summarizes comparisons of ADCP measurements made with 12 ADCPs on Sacramento River at Colusa, CA, on May 30, 2007 to discharges from a USGS gaging station. This work was done by the California WSC and other cooperating agencies. In addition to comparing discharges measured by the ADCPs, other analyses were performed such as the effect of transducer depth errors on measured discharge.
Water Mode 12: Water mode 12 in Rio Grande ADCPs is a valuable water mode for measuring in water too shallow for mode 1 and too fast for modes 5 or 11 or in water that is too slow for repeatable measurements with mode 1 and too deep for modes 5 or 11. However, Mode 12 SB should not be used as a general purpose mode. Improper use of mode 12 can result in problems caused by long delays between bottom track pings and heading, pitch, and roll updates. WinRiver II provides a better optimization of mode 12 and is recommended if making mode 12 measurements.
Baud Rate: It is generally recommended that the baud rate on an ADCP be set to the highest value, usually 115.2K baud. However, some computers, data radios, and multiplexers do not support communications at 115.2K baud. The data transmission requirement for a RiverSurveyor, which provides profiles at about 5 second intervals, is much less than for a Rio Grande, which can operate at between 2 and 3 hertz. The data transimission requirements are dependent on the number of bins being transmitted. Tests on a Rio Grande using 45 bins and 100 bins were conducted and performance was found to be impacted when the baud rate was set lower than 38.4K baud.
GPS Filters: GPS receivers often default to using filters to try and improve the position and velocity display and output. These filters can result in inaccurate boat velocities for ADCP measurements and thus should be turned off. For a complete discussion of this issue see: Use of Filters in DGPS (pdf)
Magnetic Variation: The magnetic variation for the measurement site must be entered into the data collection software (WinRiver or RiverSurveyor) if GPS is used as the navigation reference. There are several methods of determining the magnetic variation which are described in: Determining Magnetic Variation for GPS Use with ADCPs (pdf)
Baud and Update Rates: If the baud rate for the GPS receiver is set low (4800 – 9600 baud) and the update rate is set high (5-10 Hz), it is possible that the GPS receiver needs to transmit more data per second that the communications baud rate will allow. This will result in delays in the GPS data received by the ADCP software creating erroneous boat velocities and incorrect velocities and discharges. Details and recommendations for setting the baud rate for a GPS receiver can be found at: Use of GPS with ADCP's: Baud Rates and Update Rates