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 by David S. Mueller and Chad R. Wagner. Published as U.S. Geological Survey Techniques and Methods 3A-22, 2009. and OSW Tech Memo 2009.05 Publication of the Techniques and Methods Report Book 3-Section A22 and associated policy and guidance for moving boat discharge measurements || [PDF version]
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 TRDI RiverRay and the SonTek RiverSurveyor M9/S5 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. The manufacturers have verified these problems and are working on solutions. However, until solutions are delivered and tested the HaWG has developed best practice documents that can be used to achieve the best possible calibrations for the instruments in there current configuration.
Best Practice for Calibrating RiverRay
Best Practice for Calibrating RiverSurveyor M9/S5
Given the current situation, 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 until the compass calibration issues can be completely resolved.
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
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