Measuring Discharge with Acoustic Doppler Current 

Profilers from a Moving Boat

Chapter 22 of Book 3, Section A

Techniques and Methods 3–A22

U.S. Department of the Interior

U.S. Geological Survey

Measuring Discharge with Acoustic Doppler 

Current Profilers from a Moving Boat

By David S. Mueller and Chad R. Wagner

Chapter 22 of Book 3, Section A

Techniques and Methods 3–A22

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2009

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Mueller, D.S., and Wagner, C.R., 2009, Measuring discharge with acoustic Doppler current profilers from a 

moving boat: U.S. Geological Survey Techniques and Methods 3A–22, 72 p. (available online 

at http://pubs.water.usgs.gov/tm3a22).
iii

Foreword

The mission of the U.S. Geological Survey (USGS) Water Resources Discipline is to provide the 

information and understanding needed for wise management of the Nation’s water resources. 

Inherent in this mission is the responsibility of collecting data that accurately describe the physical, 

chemical, and biological attributes of water systems. These data are used for environmental and 

resource assessments by the USGS, other government agencies and scientific organizations, and the 

general public. Reliable and quality-assured data are essential to the credibility and impartiality of the 

water-resources appraisals carried out by the USGS.

The development and use of guidelines for Measuring Discharge with Acoustic Doppler Current 

Profilers from a Moving Boat are necessary to achieve consistency in the use of scientific methods 

and procedures, document the methods and procedures used, and maintain technical expertise in the 

process. USGS hydrographers and hydrologists can use this manual to ensure that the data collected 

are of the quality required to fulfill our mission.

Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat contains the most 

current information and guidance regarding acoustic Doppler current profilers (ADCPs) used by the 

USGS at the time of publication. The development of new and improved ADCPs is ongoing, as are the 

research and practical field experience with existing and new ADCPs, which likely will lead to changes 

in the guidance on the application of ADCPs over time and revisions to this document. The user is 

encouraged to log onto the USGS Office of Surface Water Web site [http://hydroacoustics.usgs.gov]

for the latest revisions to this document and technical memorandums that may be issued prior to 

revisions to ensure that the best techniques are communicated for use in collecting and processing 

ADCP discharge measurements.

Stephen Blanchard

Chief, Office of Surface Water

v

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................1

Applications...........................................................................................................................................1

Discussion of Instruments...................................................................................................................2

Predeployment Preparation.........................................................................................................................3

Data Management................................................................................................................................3

Naming Convention .....................................................................................................................3

Data Storage and Archival.........................................................................................................3

Instrument and Site Considerations ..................................................................................................3

Limitations of ADCPs...................................................................................................................3

Effect of Sediment ..............................................................................................................4

Unmeasured Areas in a Profile ........................................................................................5

Configuration and Characteristics............................................................................................6

Compass Considerations............................................................................................................8

Instrument Quality Assurance............................................................................................................8

Software and Firmware Procedures ........................................................................................9

Instrument Tests...........................................................................................................................9

Beam-Alignment Test.........................................................................................................9

Periodic Instrument Check................................................................................................9

Ancillary Equipment..............................................................................................................................9

GPS Requirements and Specifications ....................................................................................9

Echo Sounder.............................................................................................................................10

Instrument Deployments and Mounts....................................................................................10

Manned Boats...................................................................................................................10

Tethered Boats ..................................................................................................................11

Remote-Controlled Boats ................................................................................................13

Other Equipment ........................................................................................................................14

Final Equipment Preparation and Inspection.................................................................................16

Field Procedures..........................................................................................................................................16

Site Selection.......................................................................................................................................16

Pre-Measurement Field Procedures...............................................................................................17

Set Internal Clock ......................................................................................................................17

Instrument Diagnostic Checks ................................................................................................17

Speed of Sound..........................................................................................................................17

Water Temperature ..........................................................................................................18

Salinity ................................................................................................................................18

Compass Calibration .................................................................................................................18

Instrument Configuration..........................................................................................................18

Moving-Bed Tests......................................................................................................................20

Discharge-Measurement Procedures ............................................................................................21

Steady-Flow Conditions............................................................................................................21

Unsteady-Flow Conditions .......................................................................................................22

Critical Data-Quality Problems ................................................................................................22
vi

Boat Operation ...........................................................................................................................22

Estimating Edge Discharge ......................................................................................................23

Field Notes ..................................................................................................................................24

Step-by-Step Procedure...........................................................................................................24

Post-Measurement Field Procedures .............................................................................................24

Office Procedures........................................................................................................................................24

Preventive Maintenance ...................................................................................................................24

Data Storage........................................................................................................................................26

Measurement Review Procedures..................................................................................................26

Data-Quality Indicators......................................................................................................................27

Commonly Observed Measurement Problems ..............................................................................32

Selected References...................................................................................................................................32

Appendix A – Basic ADCP Operational Concepts..................................................................................35

General .................................................................................................................................................35

Measuring Velocity.............................................................................................................................35

Narrowband................................................................................................................................35

Broadband...................................................................................................................................36

Computing Velocity in Orthogonal Coordinates.............................................................................37

Measuring a Velocity Profile.............................................................................................................38

Computing Discharge.........................................................................................................................38

Measured Discharge ................................................................................................................39

Top Discharge.............................................................................................................................40

Bottom Discharge......................................................................................................................41

Edge Discharge..........................................................................................................................41

Appendix B – Collecting Data in Moving-Bed Conditions ....................................................................43

Cause and Effect of a Moving Bed ..................................................................................................43

Methods to Identify a Moving Bed ..................................................................................................44

Stationary Test with No GPS....................................................................................................44

Stationary Test with GPS..........................................................................................................45

Loop Method...............................................................................................................................46

Methods to Account for Moving-Bed Effects................................................................................47

Using GPS with ADCPs .............................................................................................................47

Alternatives to Using a GPS.....................................................................................................49

Loop Method......................................................................................................................50

Mean Correction Method.......................................................................................50

Distributed Correction Method..............................................................................50

Multiple Moving-Bed Test Method................................................................................51

Field Procedures......................................................................................................51

Processing Procedures ..........................................................................................51

Subsection Method .................................................................................................51

Average Moving-Bed Method...............................................................................52

Distributed Method using the SMBA Software..................................................52

Mid-Section Method ........................................................................................................52

Azimuth Method................................................................................................................52

Field Procedures......................................................................................................53

Processing Procedures ..........................................................................................53
vii

Appendix C – Description of Water Modes.............................................................................................54

SonTek/YSI RiverSurveyor Water Modes.......................................................................................54

TRDI Rio Grande and StreamPro Water Modes ............................................................................54

Rio Grande Mode 1....................................................................................................................54

Rio Grande Modes 5/11.............................................................................................................54

Rio Grande Mode 12..................................................................................................................55

StreamPro Mode 12...................................................................................................................55

StreamPro Mode 13, Water Mode C, Low Noise Mode......................................................55

Appendix D – Beam-Alignment Test.........................................................................................................56

Introduction..........................................................................................................................................56

Description of Procedure ..................................................................................................................56

Step-by-Step Procedure....................................................................................................................57

Appendix E – Forms and Quick-Reference Guides ................................................................................58

Appendix F – Measurement Review Procedures...................................................................................64

Figures

1. Photograph of a boat-mounted acoustic Doppler current profiler ......................................2

2. Examples of excessive backscatter and attenuation due to sediment 

in the water as displayed in intensity-profile graphs from WinRiver II...............................4

3. Diagram showing acoustic Doppler current profiler beam pattern and locations 

of unmeasured areas in each profile ........................................................................................5

4–8. Photographs of—

4. Examples of tethered acoustic Doppler current profiler boats used 

for making discharge measurements.............................................................................12

5. Temporary bank-operated cableway for making acoustic Doppler current 

profiler (ADCP) measurements with a tethered ADCP boat.......................................12

6. Motorized cableway rover for deploying tethered acoustic Doppler current 

profilers ...............................................................................................................................13

7. Examples of commercially available remote-controlled boats..................................13

8. Example toolkit of ancillary equipment for use with acoustic Doppler 

current profilers when making streamflow measurements .......................................15

9. Graph showing example of a moving bed measured with a 1,200-kilohertz 

acoustic Doppler current profiler on the Mississippi River at Chester, Illinois................20

10. Graph showing a distorted ship track in a loop caused by a moving bed ........................21

11. Diagram showing edge distances needed when using a tethered acoustic 

Doppler current profiler boat for discharge measurements ..............................................23

12. Example of completed acoustic Doppler current profiler discharge-measurement 

field note form .............................................................................................................................25

13–21. Screen captures from—

13. Teledyne RD Instruments WinRiver software illustrating numerous invalid 

ensembles collected in the Pigeon River at Canton, North Carolina, as a 

result of invalid bottom tracking......................................................................................28

14. Sontek/YSI RiverSurveyor software illustrating numerous invalid ensembles 

in the thalweg of the Mississippi River at Chester, Illinois, as a result of 

invalid bottom tracking .....................................................................................................28
viii

15. Teledyne RD Instruments WinRiver software illustrating erroneous velocity 

measurements caused by ambiguity errors..................................................................29

16. Sontek/YSI RiverSurveyor software illustrating an example of good and bad 

beam intensity data relative to detection of the streambed.......................................29

17. Teledyne RD Instruments WinRiver software illustrating an anomaly 

in beam intensities caused by interference in beam 1 from a side wall ..................30

18. Teledyne RD Instruments WinRiver software illustrating highly variable 

boat speeds resulting from shifting the motor in and out of gear while 

measuring along the transect..........................................................................................30

19. Sontek/YSI RiverSurveyor software illustrating variation in boat speed while 

measuring along a transect.............................................................................................30

20. Teledyne RD Instruments WinRiver software illustrating spikes 

in the streambed profile....................................................................................................31

21. Sontek/YSI RiverSurveyor software illustrating the effects of poor GPS 

data on the measurement of boat movement...............................................................32

Tables

1. Characteristics of SonTek/YSI RiverSurveyor acoustic Doppler current profilers ...........6

2. Characteristics of Teledyne RD Instruments Rio Grande water profiling modes 

for 1,200- and 600-kilohertz acoustic Doppler current profilers ...........................................7

3. Characteristics of Teledyne RD Instruments StreamPro acoustic Doppler current 

profiler water modes....................................................................................................................8

4. Advantages and disadvantages of acoustic Doppler current profiler mounting 

locations on manned boats.......................................................................................................11

5. List of ancillary equipment to be used with acoustic Doppler current profilers 

when making streamflow measurements ..............................................................................14
ix

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Flow rate

foot per second (ft/s) 0.3048 meter per second (m/s)

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

Temperature may be converted as follows:

°F = (1.8 × °C) + 32

°C = (°F – 32) / 1.8
x

Abbreviations and acronyms used in this report:

ABS acoustic backscatter

ADCP acoustic Doppler current profiler

ADP acoustic Doppler profiler

BB broadband

CD–ROM compact disc–read-only memory

CMG course made good

DBT depth below transducer

DC direct current

DGPS differentially corrected global positioning system

DMG distance made good

DOP dilution of precision

EMF electromagnetic field

FAA Federal Aviation Administration

GPS global positioning system

HDOP horizontal dilution of precision

Hz hertz

kHz kilohertz

LAN local area network

MHz megahertz

NMEA National Marine Electronics Association

OSW Office of Surface Water

PCMCIA Personal Computer Memory Card International Association

PDA portable digital assistant

ppt parts per thousand

RTK real-time kinematic

SMBA Stationary Moving-Bed Analysis

TRDI Teledyne RD Instruments

USB Universal Serial Bus

USGS U.S. Geological Survey

WAAS Wide Area Augmentation System

WM water mode

WM12sp water mode 12 in StreamPro

WP water ping

WV340 ambiguity velocity of 340 millimeters per second
Abstract

The use of acoustic Doppler current profilers (ADCPs) 

from a moving boat is now a commonly used method for 

measuring streamflow. The technology and methods for making ADCP-based discharge measurements are different from 

the technology and methods used to make traditional discharge 

measurements with mechanical meters. Although the ADCP 

is a valuable tool for measuring streamflow, it is only accurate 

when used with appropriate techniques. This report presents 

guidance on the use of ADCPs for measuring streamflow; this 

guidance is based on the experience of U.S. Geological Survey 

employees and published reports, papers, and memorandums 

of the U.S. Geological Survey. The guidance is presented in a 

logical progression, from predeployment planning, to fielddata collection, and finally to post-processing of the collected 

data. Acoustic Doppler technology and the instruments 

currently (2008) available also are discussed to highlight the 

advantages and limitations of the technology. More in-depth, 

technical explanations of how an ADCP measures streamflow 

and what to do when measuring in moving-bed conditions are 

presented in the appendixes. ADCP users need to know the 

proper procedures for measuring discharge from a moving 

boat and why those procedures are required, so that when the 

user encounters unusual field conditions, the procedures can 

be adapted without sacrificing the accuracy of the streamflowmeasurement data.

Introduction

The acoustic Doppler current profiler (ADCP) has 

evolved during the last 25 years from an experimental 

instrument capable of measuring velocity and computing 

discharge in deep water (greater than 11 feet (ft)) to an 

instrument that is commonly used to measure water velocity 

and discharge in streams as shallow as 1.0 ft deep (Christensen 

and Herrick, 1982; Simpson and Oltmann, 1993; Oberg and 

Mueller, 2007b). The development of the ADCP has provided 

hydrographers and engineers with a tool that can substantially 

reduce the time for making discharge measurements and 

can measure water velocities at a spatial and temporal scale 

that was previously unattainable. These instruments are used 

regularly to measure riverine and estuarine water discharge, to 

collect data for hydrodynamic model calibration and verification, to assess aquatic habitat, and to study sediment transport 

processes. Although the use of the ADCP has become common, proper instrument configuration and data-collection and 

post-processing procedures are required to collect accurate and 

reliable data.

Purpose and Scope

The purpose of this report is to present the procedures 

that should be followed when using an ADCP from a moving boat to make surface-water discharge measurements. 

The procedures for predeployment preparation, field data 

collection, and processing of collected data are discussed. A 

detailed description of how an ADCP measures velocity and 

computes discharge and additional details on selected topics 

are presented in appendixes.

Applications

The measurement of unsteady, bidirectional, and other 

flows with nonlogarithmic velocity distributions has been 

a problem faced by hydrologists for many years. Dynamic 

discharge conditions impose an unreasonable time constraint 

on conventional current-meter discharge-measurement methods, which typically take at least 1 hour to complete. Tidally 

affected discharge can change more than 100 percent during 

a 10-minute period. In addition, bidirectional flows caused by 

density currents are common in tidally affected areas and have 

been increasingly observed in freshwater environments where 

a significant temperature gradient causes a density current 

(García and others, 2007). Nearly all discharge measurements 

made using point-velocity meters have an assumed standard 

logarithmic distribution of the horizontal velocity in the 

water column; however, wind-driven currents and very rough 

bottoms in shallow water may produce nonstandard profiles. 

The introduction of the ADCP into the coastal and riverine 

environments has enabled the development of a dischargemeasurement system capable of more efficiently and more 

accurately measuring flow in unsteady, bidirectional, and 

Measuring Discharge with Acoustic Doppler Current 

Profilers from a Moving Boat 

By David S. Mueller and Chad R. Wagner
2 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

nonstandard conditions. In most cases, an ADCP dischargemeasurement system is faster than conventional dischargemeasurement systems and has comparable or better accuracy 

because ADCPs measure a much larger portion of the water 

column than conventional discharge-measurement systems. 

More efficient discharge measurements improve safety by 

reducing the amount of time a hydrographer is on a bridge, 

on a boat, or in the water. The reduction in measurement time 

realized by using an ADCP is especially beneficial when 

trying to develop an index velocity rating (Morlock 

and others, 2002; Ruhl and Simpson, 2005) at sites with 

rapidly changing flow conditions. An ADCP can define the 

rating in the transitional range of flow that was otherwise 

indefinable with conventional discharge methods. In addition 

to measuring streamflow, ADCPs are used in a variety of other 

applications including:

•	 measurement of velocity fields for calibration of 

numerical models, hydraulic studies (for example, 

safety zones near dams), and habitat assessments;

•	 in situ deployments for current measurements and for 

aiding navigation; 

•	 hydrographic surveys to measure channel bathymetry 

for use in hydrodynamic and habitat modeling applications; and

•	 estimation of sediment concentration from acoustic 

backscatter (ABS).

The application of acoustic technology in rivers and lakes has 

provided data that prior to the mid-1990s would have been 

unavailable or extremely expensive and impractical to collect.

Discussion of Instruments

The ADCP uses sound to measure water velocity. The 

sound transmitted by the ADCP is in the ultrasonic range 

(above the range heard by the human ear). The lowest 

frequency used by commercial ADCPs is around 30 kilohertz 

(kHz), and the common range for riverine measurements 

is between 300 and 3,000 kHz. The ADCP measures water 

velocity using a principle of physics discovered by Christian 

Johann Doppler (1842). Doppler’s principle relates the change 

in frequency of a source to the relative velocities of the source 

and the observer. An ADCP applies the Doppler principle by 

reflecting an acoustic signal off small particles of sediment 

and other material (collectively referred to as scatterers) that 

are present in water. The velocity measured by the Doppler 

principle is parallel to the direction of the transducer emitting 

the signal and receiving the backscattered acoustic energy. 

Typical boat-mounted ADCPs have three or four beams 

pointing between 20 and 30 degrees from the vertical. Three 

beams are required to obtain a three-dimensional velocity 

measurement. If a fourth beam is present, an additional error 

velocity can be measured (Appendix A).

In a boat-mounted system, the transducers are deployed 

beneath the water surface and aimed downward (fig. 1). 

Measurement of water velocity from a moving boat will yield 

the velocity of the water relative to the boat. ADCPs used in 

this manner account for the velocity of the boat by bottom 

tracking or through the use of a global positioning system 

(GPS). Bottom tracking determines the velocity of the boat 

by measuring the Doppler shift of acoustic signals reflected 

from the streambed; therefore, the water velocity relative to a 

fixed reference is computed by correcting the measured water 

velocity with the measured boat velocity.

Currently (2008) ADCPs can be classified into two 

groups based on the techniques used to configure and process 

the acoustic signal—narrowband and broadband. Narrowband 

is typically used in the hydroacoustic industry to describe a 

pulse-to-pulse incoherent ADCP; however, the narrowband 

ADCPs also can operate in a pulse-to-pulse coherent mode 

for short ranges. This means that in a narrowband ADCP, only 

one simple pulse is transmitted into the water, per beam per 

measurement (ping), and the resolution of Doppler shift takes 

place during the duration of the received pulse. This characteristic results in a system that is simple to configure and operate, 

but the velocity measurements made using the narrowband 

technology are noisy (have a relatively large random error). 

Narrowband systems compensate for the large random error 

by pinging fast (up to 20 hertz (Hz)) and averaging many 

pings together before reporting a velocity. Typical response 

from a narrowband system is a velocity-profile measurement 

every 5 seconds. 

Broadband systems use a ping consisting of two or 

more synchronized acoustic pulses that are encoded with a 

pseudo-random code. The encoded pulse allows multiple 

velocity measurements to be made with a single ping, thus 

reducing the random noise associated in the measured velocity. 

Figure 1. Boat-mounted acoustic Doppler current 

profiler (ADCP).

ADCP
Predeployment Preparation 3

Broadband systems are more difficult to configure because of 

the effect of the lag between the two pulses and because the 

processing of the complex pulse is slower than a narrowband 

system; however, the complex pulse results in a much lower 

random error, and the pulse pair allows configuration of the 

instrument to minimize random error for particular measurement conditions.

Predeployment Preparation

Prior to collecting data with an ADCP, it is important to 

establish standard procedures to ensure that the data collected 

will be stored in an efficient and consistent manner, the ADCP 

is in proper working order, and the ADCP is the appropriate 

equipment for making the measurement. Proper preparation 

will help avoid delays in the field, ensure complete and 

accurate data collection, and produce data that are documented 

and retrievable for future use. The required predeployment 

procedures include:

1. establishing a policy for handling and storing 

the data; 

2. ensuring that ADCP hardware and software are 

working properly and are configured consistent with 

the policies established by the U.S. Geological Survey (USGS), Office of Surface Water (OSW);

3. identifying other equipment, such as a GPS and 

boats, that may be needed; 

4. ensuring that the ADCP is capable of measuring the 

desired data for the expected field conditions; and 

5. gathering and checking the ADCP and all ancillary 

equipment for use with the ADCP.

Data Management

The ADCP and associated software can produce a large 

number of files. It is important that these files are stored in a 

manner that allows users to easily identify the location, date, 

and type of data stored in the files. Because of the volatility 

of digital data, appropriate backup and archival procedures 

should also be implemented.

Naming Convention

Each office should establish and document a consistent 

naming convention for data files. Names of files should always 

be unique and should be descriptive of the data contained. 

Site number, site name, measurement number, project name, 

project number, and date are some of the descriptive terms that 

could be used in a filename. Typically, ADCP data-collection 

software will add a suffix to the user-defined name to identify 

the type of data file (configuration, raw data, ASCII data, etc.) 

and to ensure that each file has a unique name.

Data Storage and Archival

Each office collecting electronic discharge-measurement 

data needs to have a written policy about permanent file 

storage and archiving procedures. Procedures outlined are 

based on the assumption that an office has existing systems 

and procedures for performing routine backups and permanent 

archival for electronic information stored on servers. This 

policy should detail file and directory naming conventions, 

server directory structure, how soon data must be placed on 

the server after it is collected, and how, when, and where 

server data will be archived on stable archival media. USGS, 

Office of Surface Water Technical Memorandum 2005.08 

(U.S. Geological Survey, 2005a) provides specific archival 

guidance. Paper measurement notes associated with an 

electronic discharge measurement should be filed and archived 

with other paper discharge-measurement notes in accordance 

with current office policies and procedures.

Each discharge measurement with electronic data 

files should have its own directory that contains all of the 

files collected or created as part of the measurement. These 

files include, but are not limited to, raw data, configuration 

information, moving-bed tests, instrument checks, calibration 

information, and discharge-measurement notes. The naming 

convention for the directories in the archival directory 

structure should include some combination of measurement 

number, measurement dates, water year, location, and(or) 

instrument types. 

Instrument and Site Considerations

Any site-specific information, such as maximum water 

depths and velocities from previous measurements, can be 

used as a guide for configuring the ADCP for the measurement site. Notes about conditions and locations from previous 

ADCP discharge measurements should be reviewed prior to 

the field trip.

Limitations of ADCPs

The physics associated with sound generation from a 

transducer and then propagation, absorption, attenuation, 

and backscatter in the water column result in specific 

limitations and characteristics of ADCPs. Limitations that 

will be discussed in this report include the effect of sediment 

on backscattered acoustic energy and bottom tracking, and 

unmeasured areas of a profile associated with transducer draft 

and ringing and side-lobe interference. Additional limitations 

are imposed on ADCP measurements by the techniques used 

to configure and process the acoustic signal, which vary based 

on specific user configuration of the instrument.
4 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Effect of Sediment

The quantity and characteristics of the particulate matter 

(such as sediment and aquatic life) in the water column 

can significantly affect the ability of the ADCP to make an 

accurate velocity measurement. Pure water is acoustically 

transparent because it has no suspended particulate matter 

to reflect acoustic energy. For a velocity measurement to 

be made, water must contain enough particulate matter for 

sufficient acoustic energy to be returned to the ADCP. Therefore, in very clear streams it is possible to have insufficient 

material in the water column to allow an ADCP to measure 

water velocity. High sediment loads, which are often present 

during high-flow conditions, can have the opposite effect. 

High sediment concentrations near the streambed can cause 

the ADCP to have trouble discriminating the streambed from 

the suspended-sediment concentration near the streambed, 

resulting in inaccurate water depth and(or) invalid boat 

velocity measurements (fig. 2A). In addition, high sediment 

concentrations in the water column can cause the acoustic 

signal to be attenuated before it can travel through the water 

column and back to the transducer, thus preventing the ADCP 

from making a measurement (fig. 2B). The sediment concentrations that trigger these limitations on ADCP operation 

have been observed but not quantified; these limitations 

depend on the sediment characteristics and on the water depth. 

In general, lower frequency acoustic instruments transmit 

more energy into the water and, therefore, are more capable 

of penetrating high sediment concentrations than higher 

frequency instruments.

During high flows, sediment transport near and along the 

streambed can cause a bias in the boat velocity determined 

from bottom tracking. Bottom tracking is used to determine 

the boat velocity and assumes that the streambed is stationary. 

Sediment transport near and along the streambed can cause 

a Doppler shift in the bottom-tracking ping and result in the 

boat-velocity measurement being biased in the upstream 

direction. This phenomenon is commonly referred to as a 

moving bed. If an ADCP is held stationary in a stream with a 

moving bed, a trace of the instrument motion based on bottom 

tracking shows the instrument moving upstream rather than 

being stationary. The result of a moving bed is that measured 

velocities and discharges will be biased low. Higher frequency 

instruments are more susceptible to moving-bed problems 

than are lower frequency instruments. Currently, there is no 

quantitative guidance for when a moving bed will be detected 

by an instrument, but tests to detect a moving bed are available 

and discussed later in this report. If a moving bed is detected, 

and the instrument is equipped with a compass, the use of GPS 

for measuring boat velocity is recommended. If the use of a 

GPS is not possible because of unfavorable site conditions, 

or if the instrument does not have a compass, other means to 

correct the discharge for the bias caused by the moving bed are 

available (Appendix B).

Figure 2. Examples of (A) excessive backscatter and (B) attenuation due to sediment in the water as 

displayed in intensity-profile graphs from WinRiver II.

A) Excessive Backscatter B) Excessive Attenuation
Predeployment Preparation 5

Unmeasured Areas in a Profile

ADCPs are called profilers because they provide 

measurements of velocity throughout the water column. The 

ADCP divides the water column into depth cells (also referred 

to by some software and references as bins) and reports 

a velocity for each depth cell; however, an ADCP cannot 

measure velocities at the water surface due to the draft of 

the instrument and the required blanking distance, nor can it 

measure near the bed due to side-lobe interference (fig. 3). 

The length of the unmeasured area at the water surface 

is due to the draft of the instrument deployment, the effect of 

the transducer mechanics, and the flow disturbance around 

the instrument. The ADCP must be deployed below the water 

surface and, thus, cannot measure the water velocity above the 

transducers. The required instrument draft is controlled by the 

need to prevent the instrument from coming out of the water 

and to prevent entrained air from traveling under the instrument; therefore, the required instrument draft depends on the 

shape of the instrument mount, the boat, and the relative water 

velocity (water velocity past the instrument). 

ADCPs use the same transducers to transmit and receive 

sound. When a transducer is energized to transmit sound, it 

vibrates to produce the sound waves. When the energy to the 

transducer is stopped, that transducer does not stop vibrating 

immediately; the vibrations dampen with time. The continued 

vibration of the transducer is called ringing and may be 

affected by the transducer housing and the ADCP mount. A 

good analogy of this effect is a large gong. The vibrations 

from a gong sometimes take several minutes to die out. The 

vibrations in a transducer die out much quicker than a gong, 

but sound travels some distance during the time it takes for 

the ringing to be reduced to a level where the transducer can 

accurately record backscattered acoustic signals. The distance 

that sound travels during the time it takes the ringing to be 

reduced is the minimum blanking distance. Depending on 

the frequency (typically lower frequency instruments have 

longer blanking distances) and the transducer housing, the 

blanking distance can vary from 0.16 to 3.3 ft. The flow 

disturbance caused by the instrument and its mount may also 

be a limiting factor of how close to the instrument an unbiased 

measurement of velocity can be made. Results from field data 

and numerical modeling suggest that for typical deployments, 

a blank of 0.82 ft (25 centimeters (cm)) for Teledyne RD 

Instruments (TRDI) Rio Grandes, 0.1 ft (3 cm) for TRDI 

StreamPros, and 0.66 ft (20 cm) for 3 megahertz (MHz) 

SonTek/YSI RiverSurveyors are acceptable; however, the 

deployment method and mount can influence the extent of the 

flow disturbance (Mueller and others, 2007).

Figure 3. Acoustic Doppler current profiler beam pattern and locations of unmeasured 

areas in each profile (from Simpson, 2002).

Distance along the

acoustic wave front

where vertical side lobe

interferes with the main

beam acoustic signal. Side

lobe interference is caused

by the reflection of a vertical

side lobe from the stream bed.

Main beam

(higher sound

intensity)

Side lobe

(lower sound

intensity)

Side lobe

(lower sound intensity)

Profiled

area

Water surface

Transducer depth Transducer

Blanking distance Distance that corresponds to

electronics and transducer

recovery time (after ping)

Area of side lobe

interference
6 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

ADCPs cannot measure the water velocity near the 

streambed due to side-lobe interference (fig. 3). Most 

transducers that are developed using current (2008) technology 

emit parasitic side lobes off of the main acoustic beam. The 

acoustic energy in the side lobes is much less than in the main 

beam. The amount of acoustic energy backscattered from 

scatterers in the water column in the main beam is very small 

compared to the energy transmitted. The streambed reflects 

a much higher percentage of the acoustic energy than the 

scatterers in the water column. The magnitude of the energy in 

a side-lobe reflection from the streambed is sufficiently close 

to the energy reflected from scatterers in the main beam to 

cause potential errors in the measured Doppler shift. The water 

column affected by this side-lobe interference varies from 

6 percent for a 20-degree system to 13 percent for a 30-degree 

system and can be computed as,

(1 cos( )), D D SL = ∗ − 

where

DSL is the distance from the streambed affected by 

side-lobe interference;

D is the distance from the transducer to the 

streambed; and

θ is the angle of the transducers from the 

vertical.

The frequency and the techniques used to configure and 

process the acoustic signal are important in determining the 

maximum and minimum water depths that can be measured. 

Lower frequency ADCPs typically can measure deeper than 

higher frequency ADCPs but also require larger depth cells 

and a longer blanking distance. The operational mode of some 

ADCPs determines the location of the first and last valid depth 

cells and the acceptable size of the depth cells. The ADCP 

cannot measure the velocity in the upper and lower portions of 

the water column because of the draft, blanking distance, and 

side-lobe interference; therefore, the discharge in these areas 

must be estimated from data collected in the measured portion 

of the water column. For this reason, it is recommended that a 

minimum of two depth cells be measured in the water column. 

The shallow-water limitation of an instrument is, therefore, the 

summation of the draft, blanking distance, location of the first 

depth cell, location of the last depth cell, the depth-cell size, 

and the range of the side-lobe interference. 

Configuration and Characteristics

Site conditions, such as stream depth, water velocity, 

and bed material, ultimately dictate the instrument setup 

that will provide the most accurate discharge measurement. 

Currently, narrowband ADCPs do not have specific water or 

bottom modes that the user needs to select and configure. The 

primary setup for the narrowband instruments is setting the 

blanking distance and depth-cell size. The maximum profiling 

depth, maximum relative velocity, minimum recommended 

depth-cell size, and approximate random noise (velocity 

standard deviation) for SonTek/YSI RiverSurveyor ADCPs are 

presented in table 1. 

Broadband ADCPs manufactured by TRDI offer multiple 

water and bottom modes. Although the multiple water and 

bottom modes make setup of the instrument more complicated, it allows the instrument to be optimized for the site 

conditions. Data-collection software for the Rio Grande ADCP 

from TRDI (Teledyne RD Instruments, 2003, 2007) has an 

automated configuration wizard that optimizes the instrument 

setup on the basis of the maximum expected velocity, boat 

speed, water depth, and bed material type.

Water modes offered in Rio Grande ADCPs allow the 

instrument to be optimized for the water velocity, depth, and 

bed material present at the time of the measurement. Each 

water mode has advantages and disadvantages associated 

with it. Water mode 1 is a robust multipurpose mode that 

can work in nearly all conditions, but the random noise 

associated with this mode limits the practical application in 

shallow, low-velocity situations. Water modes 5 and 11 are 

designed for low-velocity (less than 3.3 feet per second (ft/s)), 

shallow-water (less than 13 to 26 ft, depending on frequency) 

situations and have specific velocity and depth limitations. 

The advantages of water modes 5 and 11 are very low random 

Table 1. Characteristics of SonTek/YSI RiverSurveyor acoustic Doppler current profilers.

[kHz, kilohertz; ft, foot; ft/s, foot per second; m, meter; data from SonTek, 2000] 

Frequency 

(kHz)

Maximum 

profiling depth,a

in ft

Maximum 

relative velocity,b

in ft/s

Minimum recommended 

depth-cell size, 

in ft

1-second 

standard deviation, 

in ft/s

500 390 32 3.28 (1 m) 0.73 

1,000 130 32 0.82 (0.25 m) 0.89

1,500 80 32 0.82 (0.25 m) 0.68

3,000 20 32 0.49 (0.15 m) 0.38

a

 The actual maximum depth that can be profiled depends on the water temperature and sediment in suspension.

b

 The maximum velocity measured by the acoustic Doppler current profile, which includes the boat and water speeds.

(1)
Predeployment Preparation 7

errors and small depth-cell sizes. Water mode 12 is a fast 

ping-rate mode that is similar to water mode 1, but uses a 

faster ping rate and an internal averaging technique of multiple 

pings per ensemble to reduce the random noise associated 

with normal mode 1 measurements. This reduction in noise 

by mode 12 allows smaller depth cells to be used or lower 

velocities to be measured with greater accuracy. The heading, 

pitch, and roll sensors are only measured at the beginning of 

the averaging interval, and bottom-track measurements do not 

occur during the averaging interval; therefore, random instrument movements caused by poor boat operation or turbulent 

water-surface conditions are unaccounted for in mode 12 and 

can cause significant errors if the averaging interval is too 

long. A maximum averaging interval of 1 second is recommended, and this interval may need to be further reduced in 

fast, turbulent conditions. The maximum profiling depth, the 

maximum relative velocity, recommended minimum depth-cell 

size, and random noise for the various water modes available 

in TRDI Rio Grande ADCPs are summarized in table 2. It 

is possible to collect valid data when the maximum relative 

velocity is greater than the values given in table 2; however, 

this is not necessarily predictable. These values should be 

used as a guideline to help users decide to use water mode 5 

or 11. The high-resolution pulse coherent water modes 5 or 11 

should be used wherever possible. It is important to also note 

that not every Rio Grande ADCP has water mode 12; it must 

be purchased separately and installed on the ADCP. Users 

should check their instruments to determine the available 

water modes by connecting to the ADCP with a terminal 

program (such as BBTalk, Teledyne RD Instruments, 2006) 

and issuing a “WM?” command. An in-depth discussion of 

the various water modes and their applicability to various site 

conditions can be found in Appendix C.

Currently (2008) the broadband ADCPs from TRDI have 

two bottom modes available. Bottom mode 5 is the general 

purpose and default water mode, but it does not work well in 

depths of less than approximately 2.6 ft below the transducer. 

Bottom mode 7 uses multiple lags to function in depths as 

shallow as 1.0 ft below the transducer and can function to 

the full maximum depth of the profiler. The bottom mode 7 

multiple lag technique is slower, resulting in less data collected in a fixed time; therefore, bottom mode 7 typically is 

used only when bottom mode 5 fails to bottom track. 

Two water modes are available for the TRDI StreamPro 

ADCP (table 3), which is designed for use in shallow water 

(less than 13 ft) with velocities less than 6.6 ft/s, measured 

with the standard integrated float (the instrument can physically measure up to 16 ft/s). In the default configuration, the 

StreamPro ADCP is limited to twenty 0.33-ft (10-cm) depth 

cells for a maximum profiling depth of 6.6 ft. A long-range 

mode is available for the StreamPro ADCP that increases the 

maximum depth-cell size to 0.66 ft (20 cm), extending the 

maximum water depth to 13 ft. The default mode is similar to 

water mode 12, which was explained previously. The StreamPro ADCP, however, does not actually use water mode 12 as 

implemented in the Rio Grande ADCP; rather, water mode 

12 in the StreamPro ADCP (referred hereafter as WM12sp) 

is a modified multi-ping water mode 1, which pings fast. An 

Table 2. Characteristics of Teledyne RD Instruments Rio Grande water-profiling modes for 1,200- and 600-kilohertz 

acoustic Dopppler current profilers.

[kHz, kilohertz; ft, foot; ft/s, foot per second; cm, centimeter; 600-kHz values are in brackets; data from Teledyne RD Instruments, 2008]

Water mode Maximum depth,a

in ft

Maximum relative 

velocity,b

in ft/s

Minimum recommended 

depth-cell size, 

in ft

1-second standard 

deviation, 

in ft/s

1 65 [230] 32 [32] 0.82 [1.64]

(25 [50] cm)

0.31 [0.31]c

5d 13 [26]e 2.3 [3.3]f 0.16 [0.33]

(5 [10] cm)

<0.03 [<0.03]c

11d 13 [26]e 2.3 [3.3]f 0.16 [0.33]

(5 [10] cm)

<0.03 [<0.03]c

12 65 [230] 32 [32] 0.16 [0.33]

(5 [10] cm)

0.59 [0.59]g

a

 The actual maximum depth that can be profiled depends on the water temperature and sediment in suspension.

b

 The maximum velocity measured by the acoustic Doppler current profiler, which includes the boat and water speeds.

c

 Assumes a 2-hertz ping rate.

d

 Values are approximate.

e

 It is possible to profile deeper by decreasing the ambiguity velocity to 0.01 foot per second (WZ03), but this change reduces the maximum 

velocity. The WZ03 should be used with caution.

f

 The maximum velocity for modes 5 and 11 are highly dependent on depth and turbulence.

g

 Assumes 100 depth cells and an ambiguity velocity of 5.75 ft/s (WV175).
8 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

ambiguity velocity of 11 ft/s (WV340) is used, making an 

ambiguity error nearly impossible for the StreamPro ADCP 

applications. The StreamPro ADCP has a second water mode 

(water mode 13 (WM13)) that has less random noise than 

WM12sp and can be used to measure water velocities less 

than about 0.82 ft/s in water less than 3.3 ft deep. WM13 is 

a long-lag pulse coherent mode. WM13 only becomes a selectable alternative for the user when the site conditions meet the 

criteria for maximum depth (less than 3.3 ft) and maximum 

velocity (less than 0.82 ft/s).

The bottom-tracking algorithm for the Streampro ADCP 

is different than the algorithms used for the Rio Grande ADCP. 

Each ensemble contains two bottom-track pings—one at the 

beginning of the ensemble and one at the end of the ensemble. 

The placement of the pings cannot be changed by the user.

Compass Considerations

Most ADCPs reference the water and boat velocity to 

magnetic north using an internal fluxgate compass. The effect 

of compass errors on measurements made with an ADCP is 

different for water-velocity and discharge data depending on 

the boat-velocity reference. When bottom tracking is used for 

the boat-velocity reference, a compass error will cause a rotational error in the measured water velocity, but the magnitude 

of the velocity is unaffected. The compass has no effect on 

measured discharge using bottom tracking as the boat-velocity 

reference; however, when an external boat-velocity reference 

such as GPS is used, the effect of the compass is substantial. 

Potential errors include errors in the compass reading caused 

by distortion of the Earth’s magnetic field due to objects on 

the boat, displacement of the compass out of the horizontal 

position (for example, sudden acceleration or deceleration), 

and errors in determining the magnetic variation for a 

specific location. A local magnetic variation can be estimated 

from available computer models, such as Geomagix 

(http://www.interpex.com/magfield.htm) or GeoMag 

(http://www.resurgentsoftware.com/GeoMag.html), if the 

latitude and longitude of the site(s) are known. The magnetic 

variation also can be determined in the field using techniques 

described in the WinRiver User’s Guide (Teledyne RD Instruments, 2003). When using an external boat-velocity reference 

(such as GPS), compass errors will affect both measured water 

velocity and discharge. StreamPro ADCPs do not have an 

internal compass; therefore, they are not affected by compass 

errors, but they cannot be integrated with a GPS. Analytical 

assessment of the compass errors shows that the effect of these 

errors on velocity and discharge is directly proportional to the 

speed of the boat. Therefore, maintaining a boat speed that is 

slow, steady, and practical for the site conditions is imperative 

to accurately measuring water velocity and discharge when 

using an external boat-velocity reference.

The accuracy of internal compasses in commercially 

available ADCPs is typically about +/–1 to 2 degrees. Fluxgate 

compasses can be unusable when deployed with mounts or 

boats constructed of ferrous metals or substantial electrical 

fields. Use of external heading references can improve the 

accuracy of the heading measurement and eliminate problems 

associated with ferrous metals and electrical fields. Traditionally, an external heading reference was a gyroscope; however, 

improvements in GPS technology have made GPS-based 

heading measurements a cost-effective and accurate solution. 

Instrument Quality Assurance

Although ADCPs have no moving parts and typically 

require no calibration, the instruments and associated software 

and firmware are complex. Quality-assurance procedures will 

help identify potential instrument problems. The procedures 

discussed do not check all components of the ADCP but do 

identify common problems.

Table 3. Characteristics of Teledyne RD Instruments StreamPro acoustic Doppler current profiler 

water modes.

[ft, foot; ft/s, foot per second; cm, centimeter]

Water mode Maximum depth, 

in ft

Maximum 

relative velocity, 

in ft/s

Minimum 

recommended 

bin size, in ft

1-second 

standard deviation, 

in ft/s

12sp 6.6 (13)a 16 (6.6)b 0.06 0.66c

13 3.3 0.82 0.06 0.006–0.066d

a

 Maximum depth of 13 ft requires purchase of extended range mode.

b

 Instrument should measure velocities of 16 ft/s, but the integrated float was designed for velocities less than 6.6 ft/s 

with a flat water surface.

c

 Standard deviation is for 0.07 ft (2 cm) depth-cell size. For 0.66 ft (20 cm) depth-cell size, the standard deviation is 

approximately 0.1 ft/s.

d

 Standard deviation depends on signal correlation, velocity, and depth.
Predeployment Preparation 9

Software and Firmware Procedures

Upgrades to both software and firmware associated with 

ADCPs are common. Many of these upgrades result in minor 

improvements to the software or firmware and do not substantially affect the quality of discharge measurements made with 

the instrument. Nevertheless, some software and firmware 

changes can be major and can appreciably affect dischargemeasurement results. ADCP users, therefore, must ensure that 

the most recent Office of Surface Water-approved software 

and firmware will be used for data collection and processing. 

Firmware and software revisions should be tested before 

being used for routine data collection. Testing of software 

and firmware often requires data collection in a variety of 

conditions with a variety of ancillary equipment. This can be 

difficult and time consuming and often requires coordination 

between select groups of users. In addition to information 

available from instrument manufacturers, the USGS provides 

information regarding software and firmware in technical 

memorandums, a mailing list, and the OSW hydroacoustics 

Web page at http://hydroacoustics.usgs.gov/. 

Before an ADCP is taken to the field, the most recent 

OSW-approved software should be installed on the primary 

and any backup field computers. A copy of the software also 

should be kept on a storage media separate from the field 

computers, such as a Universal Serial Bus (USB) memory 

stick, compact disk-read only memory (CD-ROM), or 

memory card, in the event of damage or loss of the primary 

field computer.

Instrument Tests

Each ADCP used should be tested (1) when the ADCP 

is first acquired, (2) after factory repair and prior to any data 

collection, (3) after firmware or hardware upgrades and prior 

to any data collection, and (4) at some periodic interval (for 

example, annually). The purpose of an instrument test is to 

verify that the ADCP is working properly for making accurate 

discharge measurements. Various methods for testing ADCP 

accuracy include tow-tank tests, flume tests, and comparison 

of ADCP discharge measurements with discharge measurements from some other source, such as conventional current 

meters. Each of these methods has limitations as discussed by 

Oberg (2002).

Beam-Alignment Test

A common source of instrument bias is for the beams to 

be misaligned. The user can evaluate the potential bias caused 

by beam misalignment by a simple field test for instruments 

that have an internal compass. (This test could be applied 

to a StreamPro ADCP, but extra care would be required to 

eliminate rotation of the instrument during the test.) The 

beam-alignment test compares the straight-line distance 

(commonly called the distance made good) measured by 

bottom tracking to that measured by GPS. Detailed procedures 

for the beam-alignment test are provided in Appendix D. 

Bottom tracking is known to have a small bias caused by 

terrain effects, but this bias typically is less than 0.2 percent. 

The USGS-recommended criterion for the Rio Grande ADCP 

beam alignment to be acceptable is for the ratio of bottomtrack distance made good to the GPS distance made good to 

be between 0.995 and 1.003. For other ADCPs, sufficient data 

have not been collected to validate this criterion; however, 

the criterion is assumed to be applicable for other ADCPs. 

If the instrument does not meet the beam-alignment criterion, 

the ADCP can be returned to the manufacturer for a custom 

transformation matrix to be determined and loaded into 

the instrument. 

Periodic Instrument Check

Periodic instrument checks help ensure consistency 

among instruments and discharge-measurement techniques. 

The instrument check may be made at a site where the ADCPmeasured discharge can be compared with a known discharge 

derived from some other source, such as the rating discharge 

from a site with a stable stage-discharge rating or a concurrent 

measurement made using an independent technique. If the 

ADCP is equipped with more than one water- or bottomtracking mode, it is desirable, though not required, to periodically conduct instrument checks by using the different modes. 

Periodic instrument checks should be performed at different 

sites, so that a range of hydrologic conditions are reflected 

in the tests and so that any inherent biases associated with a 

particular site are minimized. The discharge obtained from the 

ADCP should be within 5 percent of the known discharge, but 

a consistent bias in the annual records should be investigated. 

If the comparison reference is a stable stage-discharge rating 

and the ADCP measurement departs from the discharge 

rating by more than 5 percent, it is possible that a rating may 

have shifted. Another measurement with a second ADCP or 

conventional discharge measurement should be made to check 

the validity of the rating before drawing definitive conclusions 

regarding the ADCP instrument test.

Ancillary Equipment

Although the ADCP and computer are the primary equipment, the ancillary equipment discussed in this section will 

help achieve an accurate measurement in a variety of conditions. Not all of the equipment discussed is necessary for every 

measurement; depending on the site conditions encountered, 

the appropriate equipment should be available.

GPS Requirements and Specifications

Using a GPS to measure the boat velocity is the preferred 

method of data collection when moving-bed conditions are 

present. (See Appendix B for a detailed discussion of methods 

for collecting data in moving-bed conditions.) GPS provides 

two options for determining boat-velocity differentiated 
10 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

position using the GGA National Marine Electronics 

Association (NMEA)-0183 sentence or the velocity reported 

in the VTG NMEA-0183 sentence (National Marine Electronics Association, 2002). In addition to positions, the GGA 

sentence provides time, elevation, and information about the 

satellite constellation used to reach the position solutions. The 

GPS receiver should be configured to output both GGA and 

VTG sentences.

The boat velocity is determined from the positions in the 

GGA sentence by dividing the distance between successive 

positions by the time elapsed between these position solutions 

(differentiated position). Use of differentiated position requires 

accurate position solutions and, thus, differential correction. 

Differential correction compensates for satellite and receiver 

clock drift, ephemeris inaccuracies, and tropospheric and ionospheric errors associated with the coded signal being broadcast 

by the GPS satellites and receivers. The two common methods 

of differentially correcting a GPS signal are (1) real-time 

kinematic (RTK) systems, which require a user-operated base 

station and separate rover receiver, both of which can receive 

dual frequency code-phase and carrier-phase satellite signals, 

and (2) code-phase differential corrections. RTK systems typically cost tens of thousands of dollars and deliver accuracies in 

the centimeter range. These systems are used most frequently 

where satellite-based code-phase corrections are not available 

or where high-accuracy positions are required. Code-phase differential corrections can be obtained from user-operated base 

stations but are more commonly obtained from differential 

correction services. Two free sources of differential correction 

services are provided by the U.S. Government. The first source 

is the Wide Area Augmentation System (WAAS), which 

has been developed for the Federal Aviation Administration 

(FAA) to provide precision guidance to aircraft at airports and 

airstrips. The WAAS uses a system of satellites and ground 

stations that provide GPS signal corrections (Federal Aviation 

Administration, 2006). The second source is U.S. Coast Guard 

radio beacons, which are part of a large network that provides 

differential correction to coastal areas, navigable rivers, and, 

more recently, inland agricultural areas. Some commercial 

satellite differential service providers offer differential 

corrections with various levels of accuracy for a fee. These 

corrections typically are broadcast using a communications 

satellite. The accuracy of code-phase differential corrections 

varies according to the correction source used and the characteristics of the GPS receiver. Many commercial receivers claim 

submeter accuracy using WAAS as the differential correction 

source. These receivers are the most common type of receiver 

used for ADCP data collection and range in cost from about 

$800 to $3,000. 

The velocity reported in the VTG sentence typically is 

based on measured Doppler shifts in the satellite signals. Use 

of the Doppler shifts to determine velocity does not require 

and is unaffected by differential corrections. This velocity 

measurement can be robust because it is resistant to some of 

the errors that are problematic for position determination, such 

as multipath errors and ionospheric and atmospheric distortions. Some receivers, particularly low-cost GPS receivers, 

may apply filters to smooth out the velocity or display a zero 

velocity when the velocity drops below a specified threshold. 

These types of filters and thresholds are unacceptable for using 

the GPS receiver with an ADCP. 

Experience using GPS with ADCPs has shown that the 

two most common problems are filters in the receiver and 

multipath errors caused by site conditions. The GPS receiver 

should allow all filters to be turned off. Multipath errors are 

caused by the satellite signal reflecting off of bridges, trees, 

and buildings before arriving at the antenna. Multipath errors 

affect only the position solutions; they do not affect Dopplerbased GPS velocity data. Some receivers contain special 

antennas or software to reduce multipath errors. If multipath 

errors are a problem during measurements, the use of VTG 

often is the best solution. (For additional details about the use 

of GPS with ADCPs, see Appendix B.)

Echo Sounder

Streams with high sediment concentrations of fine material and sand being transported on or near the streambed also 

may cause inaccuracies in ADCP water-depth measurements 

and, therefore, may cause an inaccurate discharge measurement. In such conditions, using a lower frequency echo 

sounder (approximately 200 kHz) to measure the water depth 

may be necessary. The echo sounder must support the NMEA 

0183 depth below transducer (DBT) data string to be compatible with ADCP data-collection software. If a depth sounder 

is used, the echo sounder needs to be properly calibrated 

as part of the premeasurement field procedures. For proper 

calibration techniques, the user is referred to the bar check 

procedures in the U.S. Army Corps of Engineers Engineering 

Design Manual on hydrographic surveying (U.S. Army Corps 

of Engineers, 2002). The bed-load transport rate and sediment 

concentration that make the use of a depth sounder necessary 

have not been quantified, and user judgment is required.

Instrument Deployments and Mounts

Every measurement site has unique features that may 

determine the best type of ADCP deployment platform. Site 

features may include hydraulic characteristics, such as water 

velocity, and access considerations, such as the presence of 

boat ramps, bridges, or cableways. Three common types of 

ADCP deployment platforms are manned boats, tethered 

boats, and remote-controlled boats. 

Manned Boats

An ADCP can be mounted on either side, off the bow, 

or in a well through the hull of a manned boat. Advantages 

and disadvantages for mounting locations on manned boats 

are listed in table 4. The ADCP should not be mounted close 

to any object containing ferrous metal or sources of strong 

electromagnetic fields, such as generators, batteries, and boat 
Predeployment Preparation 11

engines, to minimize ADCP compass errors. A good rule of 

thumb is that an ADCP should not be mounted any closer to 

a steel object than the largest dimension of that object. This is 

a general rule, however, and large variations in the magnetic 

fields are generated by different metals. Even stainless steel 

varies appreciably in the amount of ferrous material contained 

in the steel. 

ADCP mounts for manned boats should

•	 allow the ADCP transducers to be positioned free and 

clear of the boat hull and mount,

•	 hold the ADCP in a fixed, vertical position so that the 

transducers are submerged at all times while minimizing air entrainment under the transducers,

•	 allow the user to adjust the ADCP depth easily,

•	 be rigid enough to withstand the force of water caused 

by the combined water and boat velocity,

•	 be constructed of non-ferrous materials,

•	 be adjustable for boat pitch-and-roll, and

•	 be equipped with a safety cable to hold the ADCP in 

the event of a mount failure.

Photographs of a variety of ADCP mounts are available in 

USGS Open-File Report 01-01 (Simpson, 2002, p. 58–69) or 

at the USGS hydroacoustics Web page (http://hydroacoustics.

usgs.gov/).

Tethered Boats

A tethered boat can be defined as a small boat (usually 

less than 6.5 ft long) attached to a rope, or tether, that can 

be deployed from a bridge, a fixed cableway, or a temporary 

bank-operated cableway. The tethered boat should be equipped 

with an ADCP mount that meets all of the specifications 

outlined in the previous section on manned boats. The tethered 

boat also should contain a waterproof enclosure capable of 

housing a power supply and wireless radio modem for data 

telemetry. A second wireless radio modem attached to the field 

computer enables communication between the ADCP and field 

computer without requiring a direct cable connection. The 

radio modems should reliably communicate with the ADCP 

using the ADCP data-acquisition software; have a rugged, 

waterproof housing; operate on a 12-volt direct current (DC) 

power supply; and have sufficient data-communication capability to maximize ADCP data throughput. Baud rates should 

be equal to or greater than 9,600 for the RiverSurveyor ADCP 

and 38,400 for the Rio Grande ADCP (Rehmel and others, 

2002). The StreamPro ADCP operates using Bluetooth with a 

Table 4. Advantages and disadvantages of acoustic Doppler current profiler (ADCP) mounting locations on manned boats (adapted 

from Oberg and others, 2005).

Mounting location Advantages Disadvantages

Side of boat Easy to deploy

Mounts are easy to construct and are adaptable to a 

variety of boats

ADCP draft measurement can be easily obtained

Moderate chance of directional bias in measured 

discharges with some boats and flows

Possibly closer to ferrous metal (engines) or other 

sources of electromagnetic fields (EMF)

Moderate-low risk of damage to ADCP from debris or 

obstructions in the water

Susceptible to roll-induced bias in ADCP depths

Bow of boat Minimizes chance of directional bias in measured 

discharges

Mounts are relatively easy to construct

Usually far from ferrous metal or electromagnetic 

fields

Increased risk of damage to ADCP from debris or 

obstructions in the water

More difficult to measure ADCP depth

Susceptible to pitch-induced bias in ADCP depths, 

particularly at high speeds or during rough conditions 

(waves)

Well in center of boat Protected from debris and obstructions

Accurate depth measurements possible

Least susceptible to pitch-and-roll-induced bias in 

ADCP depths

Often requires special modifications to boat
12 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

fixed baud rate of 115,200. Rehmel and others (2002) describe 

the development of a prototype tethered platform, a project to 

refine the platform into a commercially available product, and 

tethered-platform measurement procedures. The StreamPro 

ADCP comes standard with a tethered boat designed specifically for the StreamPro. Tethered boats for other ADCPs, 

including boats designed to deploy the StreamPro in velocities 

greater than 5 ft/s, can be purchased commercially from the 

ADCP manufacturers or third-party vendors.

Tethered ADCP boats have become a common deployment method (fig. 4). Certain considerations need to be made 

when making tethered ADCP boat measurements. Tethered 

boats are used in a variety of settings, but primarily they are 

used from the downstream side of bridges for convenience. 

Bridge piers can cause excessive turbulence during high 

streamflow, especially if debris accumulations are present on 

the piers and the piers are skewed to the flow. The effect of 

bridge-pier-induced turbulence may be reduced by lengthening 

the tether to increase the distance between the bridge and the 

tethered boat. Attention should be paid to the cross section 

to ensure that no large eddies that could cause flow to be 

nonhomogeneous. Possible alternatives to measuring off the 

downstream side of bridges include using bank-operated 

cableways or having personnel on each bank hold a rope 

attached to the platform to pull the platform back and forth 

across the river. Bank-operated cableways may be as simple 

as a temporary “rope and pulley” apparatus (fig. 5) or may 

involve the use of a small temporary cableway with a motorized drive for towing the tethered boat back and forth across 

the stream (fig. 6). In 2004, remote-controlled rovers were 

developed for cableways. These rovers can be carried from 

one streamflow-gaging station to another and, once mounted 

on the cableway, can be used to winch up the tethered boat and 

drive the boat back and forth at a user-controlled speed. 

When the water velocity is slow (usually less than 

0.5 ft/s), controlling the tethered boat may become difficult. 

This lack of control may be exacerbated by wind, which may 

push the boat in an undesired direction. Boat handling can be 

improved by attaching a sea anchor to the back side of the boat 

to increase the effect of the current and its pull on the tether. 

Make sure that this anchor is far enough behind the 

boat so as to not disturb the flow and potentially bias the 

velocity measurements. 

When the water velocity is fast (usually greater than 

5 ft/s) or when the boat is deployed from a high bridge, it is 

not uncommon for a tethered boat to be pitched upward at 

the bow. This increased pitch is caused by increased vertical 

tension on the tether in faster flows, hull dynamics, and an 

Figure 4. Examples of tethered acoustic Doppler current profiler (ADCP) boats used for making discharge 

measurements (left photograph by Jeff Woodward, Environment Canada (used with permission); right 

photograph by Geoffrey D. Cartano, U.S. Geological Survey).

Figure 5. Temporary bank-operated cableway for 

making acoustic Doppler current profiler (ADCP) 

measurements with a tethered ADCP boat (photograph 

by Brian L. Loving, U.S. Geological Survey).
Predeployment Preparation 13

incorrect setting of the angle for the bail for those 

boats equipped with a rigid bail. The bail connects the 

tether to the boat and can be either a rigid design or a 

flexible rope bail. Large pitch angles may introduce 

some bias in depth measurements and should be 

minimized as much as practical. Adding a sounding 

weight on the tether near the location where the tether 

is tied to the boat (fig. 4) will help decrease the pitch 

angle. In addition, increasing the length of the tether 

helps reduce the pitch angle.

The tether line should be visible from the water 

surface to minimize the risk of collision with river 

traffic. Orange plastic flags tied along the tether will 

enhance its visibility. The operator should also be 

capable of releasing the tether quickly in case the boat 

becomes entangled in debris or collides with river 

traffic. Do not wind the tether around the hand to 

hold the boat because this is a safety hazard. Standard 

safety practices, site-specific traffic safety plans, and 

the local highway traffic regulations should 

be followed.

It is possible to lose control of a tethered boat 

because of a system-component failure. For example, a 

boat tether or tether attachment point could break. ADCP 

operators using tethered-boat deployments should have 

redundant attachment points for the tether on the boat and 

have a contingency plan for retrieving the boat in the event of 

a failure that causes a loss of boat control. An example of a 

contingency plan would be to carry a small manned boat that 

could be quickly and safely launched to retrieve the tethered 

boat (Oberg and others, 2005).

Remote-Controlled Boats

Unmanned, remote-controlled boats allow the deployment of ADCPs where deployment with a manned boat or 

tethered boat may not be feasible or ideal. Similar to (but 

smaller than) manned boats, a remote-controlled boat has 

self-contained motors and a remote-controlled system for 

maneuvering the boat 

across the river. Unlike 

the tethered boat, the 

remote-controlled boat 

has no rope (tether) 

restraints. Although 

remote-controlled 

boats have an increased 

risk of equipment loss 

because of potential loss 

of boat control, they 

provide the ability to 

launch a boat without a 

boat ramp and to collect 

data away from bridge 

effects (for example, 

upstream from a bridge) 

or at sites where no bridge or cableway is present. Currently 

(2008) remote-controlled boats are commercially available, 

but extensive field experience with these boats has not been 

obtained (fig. 7).

ADCP mount for a remote-controlled boat should 

meet all mount specifications previously listed for manned 

boats. The remote-controlled boat also should contain a 

waterproof enclosure capable of housing a power supply, a 

radio modem, and the control radio. Radio modems are used 

for data telemetry between the remote-controlled boat and 

field computer; the radio modems should have the capabilities 

previously described for tethered-boat deployments. 

The same operational guidelines regarding speed and 

maneuvering for manned boats also apply to remote-controlled 

boats. Proper control of a remote-controlled boat requires 

practice. The operator should be familiar with remotecontrolled boat operation prior to using this deployment 

Figure 6. Motorized cableway rover for deploying tethered acoustic 

Doppler current profilers (photograph courtesy of Water Survey of Canada).

Figure 7. Examples of commercially available remote-controlled boats (photographs courtesy of 

SeaRobotics, Inc., and OceanScience Group).

A. SeaRobotics, Inc. B. OceanScience Group
14 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

technique in high flows. Regular maintenance of the boat and 

control radios is critical to ensure reliable operation.

For remote-controlled boats, it is possible to lose control 

of the boat because of a system component failure. ADCP 

operators using remote-controlled boat deployments should 

have a contingency plan for retrieving the boat in the event of 

a failure that causes a loss of boat control. An example of a 

contingency plan would be to carry a small manned boat that 

could be quickly and safely launched to retrieve the remotecontrolled boat (Oberg and others, 2005).

Other Equipment

A serial port on a laptop computer is required for communication with the ADCP, and a second serial port is required if 

a GPS is used. New laptop computers typically do not contain 

a serial port. Use of USB or Personal Computer Memory 

Card International Association (PCMCIA) serial ports is often 

required. USB serial ports are virtual serial ports, and some 

brands to do not work well with ADCPs and(or) GPS. 

StreamPro ADCPs communicate with portable digital assistants (PDAs) and laptop computers through a wireless Bluetooth connection. An external Bluetooth radio is required for 

computers that do not have built-in Bluetooth. Prior to going 

to the field, all ports should be checked for compatibility with 

the instruments to be used. A list of some USB, PCMCIA, and 

Bluetooth serial ports that have been shown to work well with 

ADCPs can be found at the USGS hydroacoustics Web site 

(http://hydroacoustics.usgs.gov/).

In addition to the ADCP and computer, the following 

additional equipment is necessary to achieve a high-quality 

discharge measurement (table 5). 

•	 A toolkit (fig. 8) should be assembled for the ADCP 

with tools, multimeter, and any spare parts that may be 

difficult to obtain in the field (such as fuses, o-rings, 

and special wrenches). The toolkit should always be 

kept with the ADCP. 

•	 An adequate supply of the OSW-approved ADCP 

discharge-measurement field forms should be taken 

to the field. The USGS discharge-measurement form 

(9-275-I) is available from the USGS hydroacoustics Web site (http://hydroacoustics.usgs.gov/) and is 

shown in Appendix E, figure E-2. 

•	 Computer data-storage media (such as a flash-memory 

card, USB memory stick, or CD-ROM) should be 

available with sufficient storage space for making temporary backup copies of all field data files. 

•	 A thermometer is needed to check the accuracy of the 

water-temperature measurement of the ADCP because 

an incorrect temperature will bias the velocity and 

discharge measurements. 

Table 5. List of ancillary equipment to be used with acoustic Doppler current profilers when making streamflow measurements.

[USB, Universal Serial Bus; PCMCIA, Personal Computer Memory Card International Association; ADCP, acoustic Doppler current profiler; 

DGPS, differentially corrected global positioning system]

Equipment Function Optional or required

USB or PCMCIA serial port(s) Computer connection to ADCP and(or) DGPS Optionala

External Bluetooth radio Computer connection to StreamPro Optionalb

Toolkit Field troubleshooting and repairs Required

ADCP field notes Note keeping Required

Computer data-storage media Field backups of data Required

Thermometer Measure water and air temperatures Required

Measuring tape, or mount with graduated markings, 

or folding rule

Measure ADCP depth Required

Laser rangefinder or other distance-measurement tool Measure shore distances Required

Salinity/conductivity meter Measure salinity Optionalc

Hand-held anemometer Obtain estimate of wind speed Optional

ADCP cable Direct communication Required

Trolling motor or tagline Slow boat speed Optional

Hand-held radios Communication during tethered or remote-controlled 

boat measurements

Optional

 Shade/rain cover for computer Improves view of computer screen/protects screen Optional

a

 Required if computer does not support sufficient internal serial ports.

b

 Required if computer does not support internal Bluetooth communication.

c

 Required for ADCP measurements in estuaries and coastal streams.
Predeployment Preparation 15

•	 If the ADCP mount does not have graduated markings, a measuring tape or folding rule is needed to 

measure the depth of the ADCP. 

•	 The distances from the beginning and end of a 

transect to the nearest edge of water must be 

measured and input to the software for computation 

of the discharge in the unmeasured areas. Typically 

visual estimates underestimate the distance over 

water; therefore, a laser rangefinder or some other 

means of measuring the distance to shore is required. 

The calibration of distance-measurement devices 

should be checked periodically by measuring the 

distance to targets at a known distance; the results 

of these calibration tests should be recorded in an 

office log. Various types of laser and optical 

rangefinders, accuracy and limitations, and test 

results can be found on the USGS hydroacoustics 

Web site (http://hydroacoustics.usgs.gov/).

•	 A conductivity or salinity meter is required to determine the salinity at the transducer face for measurement in saline environments. 

•	 If the surface velocities are affected by wind, a handheld anemometer will allow accurate characterization 

of the wind speed and direction. 

•	 If radio modems are used for ADCP communications, 

the cable for connecting directly to the ADCP should 

be taken to the field. An ADCP connected through 

radio modems occasionally will not communicate with 

the field computer. The problem is often resolved by 

using a direct cable to establish communications and 

“reset” the ADCP for modem use. If a second pair of 

radio modems is available, they should be taken to the 

field as a backup. 

•	 If low-flow conditions are expected (generally velocities less than 0.5 ft/s), a trolling motor or tagline

may be necessary to keep boat speed slow and consistent (Oberg and others, 2005). If it is not possible 

to maintain a slow boat speed, maintain the slowest 

speed that allows smooth boat operation. (Additional 

transects may be necessary to average turbulence and 

instrument noise.) 

•	 If a remote or tethered boat deployment is used, handheld radios are helpful for communications between 

the boat operator and the computer operator.

•	 If the data-collection computer will be used in bright 

sunlight, a shade for the computer screen may be 

necessary to improve the readability of the screen. In 

potentially rainy conditions, a rain cover is required to 

keep non-ruggedized computers dry.

Figure 8. Example toolkit of ancillary equipment for use with acoustic Doppler 

current profilers (ADCPs) when making streamflow measurements (photograph by 

John M. Shelton, U.S. Geological Survey).
16 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Final Equipment Preparation and Inspection 

A pre-field inspection checklist is recommended to 

ensure that all procedures are followed and that all necessary 

equipment is available and functioning for the field trip. 

An example of a pre-field inspection checklist is shown in 

Appendix E, figure E-1; however the checklist should only be 

used as a guideline for field preparation. Other equipment may 

be necessary for the sites and conditions that may be encountered in the field. The ADCP, cables, connectors, batteries, 

mounts, and GPS or echo sounders that will be integrated with 

the ADCP in the field should be inspected for any irregularities. The ADCP should be connected to the field computer, 

and communications with the ADCP should be established 

using the ADCP data-collection software and computer to be 

used in the field. The ADCP clock should then be set to the 

appropriate reference time (usually local or Greenwich Mean 

Time). If radio modems are to be used for communications 

with a tethered or remote-controlled boat, the communications 

should be established using the radio modems. If a GPS or 

echo sounder will be connected to the ADCP in the field, then 

the GPS or echo sounder should be connected with the ADCP 

to the computer to ensure that they properly function with the 

ADCP and the ADCP data-collection software. If problems 

are encountered during any system check, the problems 

should be resolved by (1) consulting the necessary technical 

documentation, (2) calling a qualified agency staff member 

familiar with ADCPs, (3) calling the vendor technical support 

unit, or some combination of these three options.

Tethered and remote-controlled boat hulls, fins, structural 

members and compartments/hatches should be inspected. The 

tether line(s) and connectors for a tethered boat should be 

inspected for wear and to ensure that they are suitable to withstand expected field conditions. When deployed in streams and 

rivers with high velocities or turbulence, redundant attachment 

points for the tether on the boat should be used to allow the 

tethered boat to be recovered should the primary attachment 

point fail. Remote-controlled boat deployments, motors, 

servos, and the radio controller should be inspected and tested 

before going into the field (Oberg and others, 2005).

Field Procedures

Proper field procedures are critical to obtaining highquality discharge measurements using ADCPs. Although stepby-step procedures are an important aspect of high-quality 

data collection, nothing can substitute for field personnel 

who understand both the instrument and effect of hydraulic 

and sediment transport conditions. The following sections 

provide guidance on proper site selection, pre-measurement 

field procedures, discharge-measurement procedures, and 

post-measurement field procedures.

Site Selection

One of the most important steps in collecting highquality streamflow measurements is site selection. Many 

ADCP measurement problems can be solved by moving to a 

better measurement site. The guidelines provided in USGS 

Water-Supply Paper 2175 (Rantz and others, 1982, p. 139) 

for traditional current-meter measurements also are excellent 

guidelines when using an ADCP, except for those guidelines 

that relate to depth and velocity requirements for specific 

meters. General guidelines for selection of an ADCP measurement site can be categorized by location, shape, flow velocity, 

and other factors.

1. Location:

a. The cross section of a stream lies within a 

straight reach, and streamlines are parallel to 

each other. Flow is relatively uniform and free 

of eddies, slack water, and excessive turbulence 

(Rantz and others, 1982).

b. The measurement section is relatively close to 

the gaging station control to avoid the effect 

of tributary inflow between the measurement 

section and control and to avoid the effect of 

storage between the measurement section and 

control during periods of rapidly changing stage 

(Rantz and others, 1982).

2. Shape:

a. Desirable measurement sections are roughly 

parabolic, trapezoidal, or rectangular. Asymmetric channel geometries (for example, deep 

on one side and shallow on the other) should be 

avoided if possible (Simpson, 2002), as should 

cross sections with abrupt changes in channelbottom slope. 

b. The streambed cross section should be as 

uniform as possible and free from debris and 

vegetation or plant growth. 

c. Depth at the measurement site should allow for 

the measurement of velocity in two or more 

depth cells at the start and stop points near the 

left and right edges of the measurement section.

3. Flow velocity: 

a. Measurement sections with mean velocities less 

than 0.3 ft/s should be avoided if an alternative 

measurement location is available (Oberg and 

others, 2005). Although measurements can be 

made in low velocities, boat speeds must be 

kept extremely slow (if possible, less than or 

equal to the average water velocity) requiring 
Field Procedures 17

special techniques for boat control (Simpson, 

2002). If maintaining a slow boat speed is not 

possible, maintain the slowest speed that allows 

smooth boat operation. (Additional transects 

may be necessary to average turbulence and 

instrument noise.)

b. Sites with very turbulent flow, such as standing 

waves, large eddies, and non-uniform flow 

lines, should be avoided. This condition is often 

indicative of non-homogenous flow, which is a 

condition that violates one of the assumptions 

required for accurate ADCP velocity and 

discharge measurements.

4. Other factors: 

a. Measurement sections having local magnetic 

fields that are relatively large as compared to 

the Earth’s magnetic field should be avoided. 

Large steel structures, such as overhead truss 

bridges, are a common source for these large 

local magnetic fields and may result in ADCP 

compass errors. 

b. When using GPS, avoid locations where 

multipath interference is possible, such as 

where signals from the satellites bounce off 

structures and objects such as trees along the 

bank or nearby bridges or buildings. Also avoid 

locations where reception of signals from GPS 

satellites is blocked. It may be possible to make 

valid measurements in sections that violate one 

or more of the above guidelines, but whenever 

possible, locate and use a better measurement 

section (Oberg and others, 2005).

Sometimes measurements need to be made where conditions 

do not satisfy the suggested guidelines. In such situations, 

the quality of the measurement can be greatly diminished; 

therefore, the field personnel must use their best judgment in 

selecting a measurement section. 

Pre-Measurement Field Procedures

Pre-measurement tests and proper configuration of 

the ADCP help to ensure a high-quality measurement. The 

following sections describe the field procedures that should be 

completed prior to ADCP measurements. 

Set Internal Clock

Prior to the start of the discharge measurement, the 

ADCP’s internal clock should be checked, set to the correct 

time, and noted on the ADCP measurement field form. This 

should be done prior to any diagnostic tests, calibrations, or 

configuration so that time stamps on all data will be consistent. 

In most cases, the ADCP’s clock should be set to agree with 

the recorder time at the streamflow-gaging station. Checking 

and setting the correct time is of particular importance when 

using the discharge measurements to calibrate or check 

the calibration of fixed acoustic current meters installed at 

streamflow-gaging stations, or when measuring at sites where 

the flow is unsteady (Oberg and others, 2005).

Instrument Diagnostic Checks

After the ADCP is mounted and communication between 

the ADCP and field computer is established, the ADCP must 

be checked to ensure all components are operating properly. 

Diagnostic tests should be performed and the results electronically stored on the field computer. Diagnostic tests should 

include system serial number, firmware and hardware configuration versions, the beam transformation matrix, electronics 

diagnostic tests, internal system tests, and sensor verification 

tests. Software for executing diagnostic tests for some ADCPs 

is available on the USGS hydroacoustics Web site or built into 

the data-collection software available from the manufacturer. 

If software or diagnostic-test information is not available for a 

specific instrument, the user should contact the manufacturer 

for guidance. The results of diagnostic tests should be backed 

up in the field and archived in the office with the associated 

discharge-measurement files. Diagnostics tests should be 

documented on the ADCP discharge-measurement field form 

(Appendix E, figure E-2). Complete diagnostic tests should 

be made prior to every discharge measurement. If possible, 

conduct the test from a stationary boat in relatively still water, 

for example, near the shore. Some of the tests require little or 

no water motion relative to the ADCP. 

Speed of Sound

Variation in the speed of sound with depth does not 

affect the measurement of horizontal currents (Teledyne RD 

Instruments, 1996); however, it does affect the measurement 

of vertical currents and depth (range from the transducer). 

Regarding horizontal velocity measurements, Snell’s law 

states that the horizontal wave number is conserved when 

sound passes through horizontal interfaces. Because the 

frequency of the sound wave remains constant, the change in 

the speed of sound with depth does not affect the horizontal 

component of the sound velocity and hence the horizontal 

velocity measurement. The measurement of the vertical 

velocity component and the depth is proportional to the 

change in speed of sound. Currently (2008), commercially 

available data-collection and processing software do not have 

the capability for correcting the vertical velocity or the depth 

for changes in the speed of sound. Temperature and salinity 

are the two most important variables for determining the speed 

of sound for boat-mounted ADCPs.
18 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Water Temperature

ADCPs have built-in temperature sensors to measure 

water temperature at the transducer face. Temperature is the 

most important variable in the equation used to compute 

the speed of sound (Urick, 1983, p. 113). The ADCP must 

compute the speed of sound correctly to accurately measure 

velocities, depths, and compute discharge. An error of 

5 degrees Celsius (°C) in the temperature measurement will 

cause a 2-percent bias error in the measured discharge (Oberg 

and others, 2005). Thus, the temperature measured by the 

ADCP should be compared with an independent temperature 

measurement made adjacent to the ADCP. This check should 

be performed prior to every discharge measurement and 

the results recorded on the measurement field form. If the 

temperature measured by the ADCP temperature sensor differs 

consistently from the independent temperature measurement 

by 2 °C or more, or if the ADCP temperature sensor has failed, 

the ADCP should not be used to make discharge measurements until the temperature sensor is repaired and checked. 

In the event that a discharge measurement is necessary and 

another ADCP is not readily available, it may be possible to 

enter a temperature manually for use in the speed-of-sound 

calculations. This action is not recommended as standard 

practice, however, and it may decrease the accuracy of the 

discharge measurement.

Salinity

Salinity is another important variable in the speed of 

sound equation. Salinity values generally range from zero 

parts per thousand (ppt) for freshwater to 35 ppt for water 

from the open ocean. When measuring in waters where the 

salinity is greater than zero, the salinity should be measured 

near the transducer face and recorded on the field form. 

The salinity value may then be entered into the ADCP 

data-collection software prior to data collection and 

adjusted as necessary during measurement playback and 

processing. Salinity should be measured for every transect in 

locations where salinity varies over time. Salinity may also 

vary from bank to bank. It should be noted that the salinity 

value used for a transect should reflect an average salinity for 

the section to be measured at the approximate depth of the 

ADCP transducers.

Compass Calibration

Calibrating the internal magnetic compass of instruments 

with an internal compass is encouraged prior to all ADCP 

measurements, but is mandatory when using GPS as the 

navigation reference, using the loop method for correcting 

discharge for bias caused by a moving bed (Mueller and 

Wagner, 2006), or when the velocity direction is important. 

The instrument-specific procedures available from the 

manufacturer for calibrating the compass of the ADCP being 

used should be followed. An automated program from some 

ADCPs is available on the USGS hydroacoustics Web site 

(http://hydroacoustics.usgs.gov/). The following guidelines 

should be followed for successful compass calibrations: 

1. Minimize ferrous material and electromagnetic field 

(EMF) interference located in the vicinity of the 

ADCP (on the boat and at the measurement site). 

EMF and ferrous material may adversely affect the 

performance of the internal magnetic compass.

2. If the instrument calibration or evaluation process 

reports a total compass error, this error should be 

less than 1 degree when evaluated after calibration. If the error reported by the compass evaluation 

exceeds 1 degree, the calibration procedure should 

be repeated. If after several attempts, the total compass error cannot be reduced to less than 1 degree, 

the compass error should be noted on the field sheet. 

The discharge measurement then can be made, but 

special attention should be paid to potential compass 

errors, such as directional bias and irregular ship 

track. If the instrument does not report a numerical 

error, the instrument should report an “excellent” rating for the horizontal calibration parameter.

3. Pitch-and-roll changes must be minimized with Rio 

Grande ADCPs because they are equipped only for 

a single-tilt calibration process. In such situations, 

the standard deviation of the pitch-and-roll should 

be less than 1 degree and, ideally, 0.5 degree or less 

during the calibration and evaluation process. For 

RiverSurveyor ADCPs, pitching and rolling the 

instrument is encouraged during the calibration, but 

only the rating of the horizontal calibration is of 

major concern.

4. Compass calibration should be done as close to 

the measurement site as possible with the ADCP 

mounted in the same manner as it will be deployed 

for the measurement.

5. For best results, the maximum rotation velocity 

should be 5 degrees per second or less. 

Instrument Configuration

The ADCP should be configured by a trained user to 

reflect the hydrologic conditions at the site and to optimize the 

data quality (Lipscomb, 1995). ADCP configuration parameters that must be set include the blanking distance, water 

mode (if applicable), depth-cell size, and profiling range. 

Other parameters that should be set prior to data collection but 

can be modified during postprocessing include the instrument 

draft, edge shape, top and bottom extrapolation method, and 

magnetic variation. Configuration parameters are specific to 

the type (narrowband or broadband), the manufacturer, and the 

model of the ADCP being used. For a detailed description of 
Field Procedures 19

all configuration parameters, refer to the technical documentation for the specific ADCP. General recommendations for 

configuration parameters are given below.

1. File names for the data files collected (also called 

deployment names) should follow a uniform, 

documented convention developed by each office 

involved in ADCP operation (U.S. Geological Survey, 2005a). 

2. The depth of the ADCP (vertical distance from the 

water surface to the center of the transducer face) 

must be measured accurately, recorded in the ADCP 

discharge-measurement notes, and entered into the 

configuration file. The pitch-and-roll of the boat 

when the depth is measured should be similar to the 

pitch-and-roll during the discharge measurement. If 

the depth of the ADCP changes during the measurement, the depth must be measured again, noted, and 

the configuration file modified with the new depth. 

3. Most ADCP data-collection software contains an 

automated method to configure the ADCP. The automated methods are dependent upon user-supplied 

information about site characteristics, such as maximum water depth, bed-material characteristics, and 

expected maximum water and boat speeds. Where 

these methods are available in ADCP data-collection 

software, the software should be used to configure the ADCP for discharge measurements (U.S. 

Geological Survey, 2003). The commands generated 

by this software utility, however, should be checked 

prior to the start of the measurement. 

4. The configuration parameters and the site conditions 

entered into an automated configuration program 

should be documented in the field notes. Changes 

made to the ADCP configuration during a measurement should be documented on the measurement 

field note forms, so it is clear that changes were 

made and to which transects these changes apply.

5. Manual configuration of an ADCP should only be 

used in rare cases where the automated procedures 

are not applicable. The most up-to-date agencyspecific guidelines for the instrument should be 

understood before attempting a manual configuration. If guidelines are not available, the user should 

use manufacturer recommendations for the unit. 

Also, seek advice from USGS ADCP experts. 

6. Configuration of the ADCP to collect single-ping 

water data is preferable, if random noise levels do 

not prohibit this configuration. Collection of singleping data allows possible data-quality problems to be 

more easily identified than problems with multi-ping 

averaged data. When collecting multi-ping averaged 

data, the user should be aware of how often the 

heading, pitch, and roll sensors are recorded and how 

often water depth and boat velocity are measured. 

Typically, this is done automatically in most narrowband ADCPs, but the flexibility provided by water 

mode 12 in broadband ADCPs allows the user to set 

a configuration that is not optimal for moving-boat 

deployments. If the averaging interval is too long for 

the boat stability and water turbulence, errors can be 

introduced into the measurement. 

7. The extrapolation method for the top and bottom 

unmeasured zones must be specified unless data 

are collected with a StreamPro ADCP on a PDA, 

in which case, the extrapolation methods default to 

the one-sixth (0.1667 power coefficient) power law 

on the top and bottom for data collection. Often, the 

appropriate extrapolation method cannot be determined until after the measurement during postprocessing. Previous data collected at a site may 

be used to guide the selection of the extrapolation 

method. In the absence of any other information, the 

one-sixth power-law extrapolation method is a good 

technique for most open-water discharge measurements made during steady-flow conditions. The 

extrapolation methods should be evaluated and, if 

necessary, changed during post-processing.

8. Wind speed can be important, especially for sites 

with low velocities where wind can greatly affect 

the surface velocities and influence the top extrapolation method to be applied. Overall wind speed 

and direction, as well as changes between transects, 

should be noted on all measurement field note forms 

to assist with accurate processing and reviewing 

of measurements.

9. If the user is unfamiliar with the measurement 

section, a trial transect, which may or may not be 

recorded, should be made across the river. A trial 

transect is useful for determining the following characteristics of the proposed measurement: 

a. maximum water depth;

b. overall cross-section shape;

c. maximum water velocity and its location in the 

cross section;

d. flow uniformity;

e. effects of hydraulic structures, such as bridges, 

piers, and islands, on the flow;

f. unusual flow conditions, such as reverse or 

bi-directional flow;

g. bank shapes; and
20 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

h. approximate start-and-stop locations on the left 

and right banks, where a minimum of two depth 

cells with valid velocity measurements can be 

measured. (To obtain consistent edge estimates, 

buoys can be used to mark the start-and-stop 

locations.)

The information gleaned from the trial transect should be 

recorded on the discharge-measurement notes.

Moving-Bed Tests

ADCPs can measure boat velocity using a technique 

called bottom tracking, which computes the Doppler shift of 

acoustic pulses reflected from the streambed. This technique 

assumes that the streambed is stationary; however, sediment 

transport on or near the streambed can affect the Doppler shift 

of the bottom-tracking pulses. In such situations, reflections 

of bottom-tracking pulses from highly concentrated near-bed 

sediments contaminate the reflections from the bed. These 

near-bed sediments typically are being transported in the 

downstream direction. If bottom tracking is affected by sediment transport, the measured boat velocity will be biased in 

the opposite direction of the sediment movement. A stationary 

boat in the stream would appear to be moving upstream 

(fig. 9). This bias in the boat velocity will result in measured 

velocities and discharge that are less than the true velocities 

and discharge (negative bias). 

USGS policy (U.S. Geological Survey, 2002b; Oberg and 

others, 2005) requires that a moving-bed test be conducted 

prior to making a discharge measurement. In USGS training 

classes and in Oberg and others (2005), an exception to 

conducting a moving-bed test with every measurement was 

allowed if sufficient documentation was provided 

in the field folder to justify not conducting a 

moving-bed test. Field experience has shown 

that sediment transport characteristics can vary 

greatly for the same discharge, depending on the 

hydrograph shape, source of runoff, and season of 

the year. Thus, a moving bed may be detected at a 

location and discharge where one was not previously detected, or a moving bed may no longer 

exist at a location and discharge where one was 

previously detected. Moving-bed conditions also 

have been observed in low-velocity environments 

(less than 1 ft/s) and are likely caused by organic 

material transported by the water. Therefore, to 

ensure the quality of the data collected, every 

moving-boat measurement made with an ADCP 

must have a recorded moving-bed test. If a site 

routinely has a moving bed and GPS is always 

used with the ADCP, a moving-bed test is still 

required but need only be 5 minutes in length. This 

requirement supersedes Oberg and others (2005) 

and various USGS training materials.

A moving-bed test is only useful if proper techniques are 

followed in conducting the test and analyzing the results. The 

three acceptable methods for performing a moving-bed test are 

(1) stationary test with no GPS, (2) stationary test with GPS, 

and (3) the loop method. A brief summary of each method 

is provided here, and detailed descriptions of these methods 

are provided in Appendix B along with data-collection and 

processing methods that can be used to obtain an unbiased 

discharge measurement if a moving bed is present. 

The stationary test with no GPS requires that the boat 

with the ADCP be held in a stationary position while recording ADCP data, using bottom tracking as the boat-velocity 

reference. If the stationary position is maintained by a tether 

or anchor so that upstream or downstream movement of 

the ADCP is not possible, the moving-bed test should be 

recorded for no less than 5 minutes; however, if the ADCP 

can move either upstream or downstream, such as when the 

boat operator is trying to maintain position of the boat, the test 

should be recorded for no less than 10 minutes. These criteria 

supersede the guidance on stationary moving-bed tests that 

have been published previously in U.S. Geological Survey 

(2002b) and Oberg and others (2005). When a moving-bed 

condition is present, a stationary boat will appear to have 

moved upstream (fig. 9). The error caused by the moving 

bed can be estimated by dividing the distance of the apparent 

boat motion in the upstream direction by the duration of the 

test in seconds. This computation will provide an estimate of 

the moving bed detected by the bottom-tracking technique. 

This moving-bed velocity can then be divided by the average 

water velocity and the moving-bed velocity, and multiplied 

by 100 to yield the percent bias error for a water-velocity 

measurement at this stream location. If the moving-bed test 

was completed with a fixed tethered deployment, an anchored 

Figure 9. Example of a moving bed measured with a 1,200-kilohertz acoustic 

Doppler current profiler (ADCP) on the Mississippi River at Chester, Illinois. DISTANCE NORTH, IN FEET

-350 -300 -250 -200 -150 -100 -50 0 50

-50

0

100

50

150

250

200

DISTANCE EAST, IN FEET

End

Start

Ship track

Flow direction
Field Procedures 21

manned boat, or a manned boat where little movement of the 

boat was ensured, a moving bed is determined to be present 

when the measured moving-bed velocity is greater than 

1 percent of the mean water velocity at the test location. If 

the moving-bed test was conducted using a manned boat that 

was not anchored and may have moved either upstream or 

downstream, a criteria of 2 percent instead of 1 percent is used 

because uncertainty has been introduced into the test by the 

boat’s movement. Discharge-measurement techniques that are 

not affected by a moving bed, or that correct for the effect of a 

moving bed, should be used if a moving bed has been detected 

(Appendix B). 

A more accurate method for estimating the errors 

introduced by a moving bed can be determined if a GPS is 

available for use and is interfaced with the ADCP and the 

data-collection software. This second method also requires 

that the ADCP boat be held in a stationary position and a 

data file recorded for at least 5 minutes, if quality GPS data 

are being recorded. The error caused by the moving bed can 

be computed in the same manner as previously described 

for the first method, except that the distance in the upstream 

direction indicated by bottom tracking should be corrected by 

the distance actually traveled in that direction, as indicated 

by GPS (Oberg and others, 2005). In the WinRiver software, 

this distance can be found in the “compass calibration” tabular 

window and is labeled “BMG-GMG mag,” and the direction 

of the “BMG-GMG dir” should be in the upstream direction. 

If the measured moving-bed velocity is greater than 1 percent 

of the mean water velocity at the test location, dischargemeasurement techniques that are not affected by a moving 

bed, or that correct for the effect of a moving bed, should be 

used (Appendix B).

If the ADCP can be held stationary, stationary 

moving-bed tests are a good measure of the magnitude of an 

apparent moving streambed; however, these tests represent 

moving-bed conditions for only one location in the cross 

section. An alternative to the stationary moving-bed test is 

the loop method, which is based on the fact that as an ADCP 

is moved across the stream, a moving bed will cause the 

bottom-track-based ship track to be distorted in the upstream 

direction. Therefore, if an ADCP makes a two-way crossing 

of a stream (loop) with a moving bed and returns to the exact 

starting position, the bottom-track-based ship track will 

show that the ADCP appears to have returned to a position 

upstream from the original starting position (fig. 10). The 

mean moving-bed velocity can be computed from the distance 

the ADCP appeared to have moved upstream from the starting 

position (loop-closure error) and the time required to complete 

the loop. If the moving-bed velocity measured by the loop 

method is greater than 0.04 ft/s and greater than 1 percent of 

the mean water velocity, a moving bed is present. Dischargemeasurement techniques that are not affected by a moving bed, 

or that correct for the effect of a moving bed, should be used 

if a moving bed has been detected (Appendix B). The loop 

method must be applied properly, or it may produce incorrect 

results. Anyone planning to use the loop method should read 

and follow USGS Scientific Investigations Report 2006–5079 

(Mueller and Wagner, 2006), which describes the procedures, 

limitations, and uncertainties associated with the loop method. 

A detailed description of the loop method also is presented in 

Appendix B.

Discharge-Measurement Procedures

The procedures to be followed to make quality discharge 

measurements vary depending on the flow conditions 

being measured. The procedures for measuring steady-flow 

conditions are different from the procedures used to measure 

unsteady-flow conditions. Although the procedures may be 

different for the various flow conditions, the data-quality 

indicators for both conditions are consistent. The following 

sections provide details on the recommended procedures for 

measuring discharge in steady- and unsteady-flow conditions 

as well as data-quality problems to monitor in the field when 

making discharge measurements.

Steady-Flow Conditions

A discharge measurement in steady-flow conditions 

is obtained from the measurement of a minimum of four 

transects (two in each direction). The measured discharge is 

the average of the discharges from the four transects. If the 

discharge for any of the four transects differs by more than 

5 percent from the mean measured discharge and no critical 

data-quality problem can be identified and documented, a 

minimum of four additional transects should be obtained, and 

the mean of all eight transects will be the measured discharge 

(U.S. Geological Survey, 2002b). If the discharge for one or 

more transects is not within 5 percent of the mean measured 

discharge and a critical data-quality problem can be identified 

Figure 10. A distorted ship track in a loop caused by a 

moving bed. DISTANCE NORTH, IN METERS

-100 -50 0 50 100 150

-250

-200

-150

-100

-50

50

0

Dup = Apparent Distance

 Moved Upstream

DISTANCE EAST, IN METERS
22 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

and documented (for example, a tow boat approaching the 

section, a sudden change in discharge because of a lockage, 

communication problems between the computer and ADCP, 

or other factors), the transect deviating from the mean may 

be replaced with an additional transect collected in the same 

direction. Reciprocal transects should always be measured to 

reduce potential directional biases. Directional biases occur 

when the discharges measured for transects from the left bank 

to the right bank are consistently either greater than or less 

than discharges measured for transects made from the right 

bank to the left bank. 

When the mean channel velocity is less than 0.8 ft/s, 

the TRDI StreamPro ADCP discharge measurements for 

individual transects have much greater variability than those 

StreamPro measurements made when the mean channel 

velocity is greater than 0.8 ft/s. Discharge measurements made 

when mean velocities were less than 0.8 ft/s had an average 

coefficient of variation for individual transect discharges 

of 12 percent, whereas measurements with mean velocities 

greater than 0.8 ft/s had an average coefficient of variation 

of 2.5 percent. Despite this larger variation, the measured 

discharges (the mean discharge for all transects) do not seem 

to be biased, provided that enough transects (potentially more 

than eight) are included in the mean discharge. When using a 

StreamPro ADCP in these slow conditions, a slow, steady boat 

speed is critical, and water mode 13 (WM13) should be used if 

the site conditions meet the criteria for maximum water speed 

(less than 0.8 ft/s) and depth (less than 3.3 ft). Additional 

details on the StreamPro ADCP testing results can be found 

in OSW Technical Memorandum 2005.05 (U.S. Geological 

Survey, 2005b).

Unsteady-Flow Conditions

At times, flow changes rapidly enough that discharge 

measurements within 5 percent of the mean cannot be collected from four transects. Unsteady flows can be caused by 

upstream dam or lock regulation, tidal effects, downstream 

backwater effects, flood waves, or other conditions. It may 

be necessary to use measurements from individual transects 

as discrete measurements of discharge if the flow is changing 

rapidly. If possible, however, pairs of reciprocal transects 

should be averaged together as one measurement of discharge 

to reduce the potential of directional bias (U.S. Geological 

Survey, 2002b). The justification for using a single transect 

or pairs of transects for discharge measurements should be 

documented in the field notes and stored with the discharge 

measurement or applicable station analysis files. Another 

consideration for unsteady flows, specifically bi-directional 

flows, is the assignment of a positive or negative sign to the 

discharge measurement. The ADCP software may or may not 

assign flow direction correctly, and the positive or negative 

sign also can change depending on which edge is designated 

“left” or “right.” Thus, the operator should note the direction 

of flow during measurement for each transect, according to 

accepted convention for a particular site. 

Critical Data-Quality Problems

When making ADCP discharge measurements, the 

ADCP operator should continuously monitor the data through 

the ADCP software. If a critical data-quality problem is 

observed during measurement at a transect, the use of that 

transect may be terminated. If a transect is not used, the reason 

should be documented on the ADCP discharge-measurement 

field note form, and that transect should not be used in the 

computation of measurement discharge. If the problem was 

related to undesirable measurement-section characteristics, a 

new measurement section should be located and noted on the 

measurement field note form. If the terminated transect was 

not the first transect in a measurement series, the boat should 

be returned to the initial starting point to ensure the transects 

are measured in reciprocal pairs (Oberg and others, 2005). 

Potential critical data-quality problems can include, but are not 

limited to the following:

a. inappropriate or improperly configured water or 

bottom mode;

b. configuration errors, such as an insufficient 

number of depth cells to profile down to the 

channel bed;

c. appreciable or consistent portion of the section 

with invalid or missing data (invalid data failed 

to meet internal and user-specified data-quality 

criteria, and missing data are a result of communication problems between the computer and 

the ADCP);

d. appreciable invalid bottom tracking;

e. erroneous boat or water velocities, such as 

ambiguity errors (Appendix A);

f. excessive boat speed;

g. poor GPS data attributed to multipath, satellite 

changes, or high dilution of precision (DOP);

h. excessive pitch-and-roll or erratic motion of 

boat and ADCP; and,

i. inadvertent early termination of the transect. 

Boat Operation

Average boat speed during each transect normally should 

be less than or equal to the average water speed. At some 

sites, it may be necessary to move the boat across the channel 

using a non-ferrous tag line in order to meet this requirement. 

Other methods for moving the boat slow enough to be equal 

to or less than the water speed include the use of push poles, 

paddles, low-speed trolling motors, or tethered boats, which 

can be moved slowly across the channel when deployed from 
Field Procedures 23

a hand-operated cableway or a bridge. In certain conditions, 

it may not be possible to keep the boat speed less than the 

water speed. If it is not practical or safe to keep the boat 

speed less than or equal to the average water speed, additional 

transects may be measured to obtain a good average discharge. 

The reason that the boat speed was higher than the average 

water speed should be documented on the ADCP dischargemeasurement field note form. Ongoing research (Oberg and 

Mueller, 2007a) indicates that the number of transects and 

the boat speed are not as important as the cumulative time 

in which data are collected and averaged. A cumulative time 

for data collection of at least 720 seconds should result in a 

good mean discharge in steady-flow conditions. When using 

GPS, keeping the boat speed as low as practical is especially 

important because errors in the compass readings are additive 

and increase with boat speed. Rapid course changes should be 

avoided; the key element in boat operation during the measurement is to do everything slowly and smoothly. Simpson (2002) 

discusses proper boat operation for ADCP measurements in 

detail, and his remarks on boat operation should be heeded 

(Simpson, 2002, p. 122): 

“Be a smooth operator! The BB [broadband]-ADCP 

discharge-measurement system will give more 

consistent results if rapid movements and course 

changes are kept to a minimum. Smooth boat motion 

is more important than a straight-line course.”

Estimating Edge Discharge

Because depths will eventually get too shallow 

for valid data collection as the ADCP approaches 

a bank, it is necessary to estimate discharge in the 

near-shore unmeasured zones using the ADCP 

discharge-measurement software. To ensure the 

accuracy of near-shore discharge estimates, the 

distances from the edge of water to the starting and 

stopping points of each transect must be measured 

using a distance-measurement device (such as a 

laser or optical rangefinder), tagline, or some other 

accurate measurement device. Placing marker 

buoys at the start and end points of transects is 

advantageous for keeping consistent edges. Use 

of marker buoys enhances the data collection by 

ensuring more consistent edge estimates and by 

measuring in approximately the same section for all 

passes. When measuring in channels with vertical 

walls at the edges, start and stop points for transects 

should be no closer to the wall than the depth of 

water at the wall to prevent acoustic interference 

from the main beam or side lobes impinging on the 

wall. For example, if the depth at a vertical wall 

is 10 ft, transects should start or stop at least 10 ft 

away from the wall. In order to obtain an accurate 

mean velocity for estimating the discharge in the 

near-shore zones, the boat should be kept nearly 

stationary from 5 to 10 seconds at the beginning and end of 

each transect. Accurate edge-discharge estimates also require 

the ADCP operator to select the correct edge-shape coefficient 

for the type of edge (sloping or vertical). The edge shapes 

should be recorded in the ADCP discharge-measurement notes 

(Oberg and others, 2005).

When using a tethered boat, special methods are required 

to measure edge distances. Distance marks on the bridge 

handrail or guardrail may be used to measure edge distances 

(fig. 11). If the tethered boat is too far away from the bridge to 

accurately use distance marks for measuring edge distances, 

laser rangefinders having a compass, an inclinometer, and a 

“missing-line mode” capability may be used. Missing-line 

mode calculates a horizontal distance between two points, 

given a range, heading, and vertical angle measured for each 

point. Edge distance may be measured by selecting the shore 

and the transect start or end point while using this mode 

(Rehmel and others, 2002).

When using a remote-controlled boat at some sites, edge 

distances may be measured using the same techniques as with 

tethered boats. At other sites where edge distances cannot be 

measured using these techniques, it may be necessary to have 

someone in line with the measurement section to measure the 

distance from the near-shore edge of water to the starting point 

and the distance from the ending point to the edge of water on 

the far shore.

Figure 11. Edge distances needed when using a tethered acoustic 

Doppler current profiler boat for discharge measurements (modified from 

Environment Canada, 2004).
24 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Field Notes

All information on an ADCP measurement field note 

form should be filled out during the course of the measurement. The ADCP operator should note any conditions that 

potentially could affect the measurement, including estimated 

wind speed and direction, bi-directional or unusual flow 

patterns, excessive waves, or passing boats. Use of an ADCP 

does not negate long-standing, agency guidelines and policies 

regarding measurement documentation, such as recording 

reference gage heights before, after, and, if needed, during the 

discharge measurement. An example of a completed USGS 

ADCP discharge-measurement field note form is shown in 

figure 12 (Oberg and others, 2005).

Step-by-Step Procedure

The steps for making a discharge measurement using 

an ADCP are not complex, but each step must be completed 

to ensure quality data. To assist the field hydrographer, 

quick-reference guides that detail the step-by-step procedure 

for making ADCP discharge measurements, along with 

other pertinent information, are presented in Appendix E, 

figures E-3–E-6. These guides can be printed, laminated, and 

kept with the ADCP for reference.

Post-Measurement Field Procedures

An assessment of the discharge measurement should 

be made after completion of the transects composing the 

measurement. A thorough review of all measurement data 

may not be practical in the field, but a cursory review of the 

measurement should be made in order to assign a preliminary 

quality rating to the measurement and to ensure that specific 

transects do not have critical data-quality problems. If all data 

were collected at the same measurement section, the transect 

widths and discharges in the measured (middle) and unmeasured (top, bottom, and edge) sections should be consistent. 

If transect widths or discharges are not consistent with those 

of the other transects, the transect data should be scrutinized 

to determine if a critical data-quality problem occurred 

(examples of critical data-quality problems are listed in the 

Discharge-Measurement Procedures section of this report). 

If a critical data-quality problem is identified, the data from 

the affected transect should not be used in the computation of 

discharge. A new transect should be measured, starting from 

the same side as the discarded transect, if flow conditions have 

remained steady. If the flow has changed, a new transect series 

should be collected. A minimum of four transects should be 

measured if the flow is stable when the new discharge data 

are collected. A transect should be discarded only if a critical 

data-quality problem is identified and documented on the field 

note form. Site-specific conditions, such as turbulence, eddies, 

reverse flows, surface waves, moving bed, high sediment 

concentration, and proximity of the instrument to ferrous 

objects, should be noted under the appropriate sections on the 

ADCP measurement field note form and used in assigning a 

quality rating for the measurement (Lipscomb, 1995).

If the discharge measurement was collected at a site 

with a rating curve, the measured discharge should be plotted 

on the rating curve for that streamgaging station, and the 

percentage of difference from the stage-discharge rating 

should be computed. Rantz and others (1982, p. 346) state: “If 

the discharge measurement does not check a defined segment 

of the rating curve by 5 percent or less, or if the discharge 

measurement does not check the trend of departures shown by 

recent measurements, the hydrographer is normally expected 

to make a second discharge measurement to check his original 

measurement.” Rantz (1982, p. 346–347) then describes 

procedures for making check discharge measurements 

with mechanical current meters. For ADCPs, power off all 

equipment and begin with step 1c in figure E-3 of Appendix 

E and proceed through the remainder of the procedures. If 

practical, choose a new measurement cross section for the 

check measurement. The measured discharge from the check 

measurement should then be plotted on the rating curve, and 

the percentage of difference from the discharge rating should 

be computed in the field.

Immediately after completion of a measurement, all 

files, including raw data files, configuration files, instrument 

test files, compass calibration files, and any electronic measurement forms, should be backed up on nonvolatile media, 

such as CD-ROMs, flash-memory cards, or USB drives, and 

stored separately from the field computer. The purpose of this 

backup is to preserve the data in the event of loss or failure of 

the field computer.

The ADCP should be dried after use and stored in its 

protective case for transport. When working in estuaries and 

other saltwater environments, the ADCP must be rinsed off 

with freshwater and dried prior to storing for transport. Failure 

to dry the ADCP may result in corrosion of the ADCP connectors, mounting brackets, and any ADCP accessories stored in 

the protective case (Oberg and others, 2005).

Office Procedures

Upon returning to the office from field data collection, 

routine maintenance of equipment should be completed, all 

data files and notes should be stored properly, data should be 

reviewed, and measurements should be finalized and archived. 

Adherence to these procedures will ensure the equipment is 

ready for the next deployment and that data are reviewed and 

processed in the most efficient manner.

Preventive Maintenance

 The ADCP and associated accessories, such as GPS, 

vertical depth sounders, and electronic rangefinders, should 

be inspected upon returning from the field to determine their 
Office Procedures 25 Figure 12. Example of completed acoustic Doppler current profiler discharge-measurement field note form (Oberg and others, 2005).

1,500
26 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

condition. Deployment platforms and mounts also should be 

inspected. Damage or undue wear to any instrument components, deployment platforms, or mounts should be corrected 

as soon as possible. The ADCP, all accessories, platforms, 

mounts, and field computers should be prepared for redeployment and stored in an appropriate location. All batteries should 

be recharged immediately to facilitate rapid reuse.

Data Storage

All measurement data should be moved from the field 

computer or field backup media to a permanent storage location for archival and backup. Field computers used to collect 

ADCP data should have local area network (LAN) capability 

to facilitate the process of transferring the measurement data 

to an office server.

Measurement Review Procedures

Discharge measurements should be reviewed in detail by 

the person who made the measurements as soon as practical 

after completion of ADCP field measurements. ADCP 

discharge measurements should be routinely checked by 

someone other than the person who made the measurement, in 

accordance to specific agency policies.

Important aspects of reviewing ADCP discharge measurements both in the office and in the field as soon as the data 

are collected are listed below.

1. The discharge-measurement field note forms should 

be complete, understandable, and legible.

2. All electronic data files associated with the measurement should be backed up in the field and archived 

on an office server.

3. The number of transects measured should be 

appropriate for the flow conditions and satisfy 

agency policy. Transects should be measured in 

reciprocal pairs.

4. Configuration files should be checked for errors, 

appropriateness for the hydrologic conditions, 

and consistency with field notes. ADCP depth, 

salinity, edge distances, edge shapes, extrapolation 

methods, and ADCP configuration parameters listed 

on the field notes should match those in the configuration file.

5. The temperature measured by the ADCP thermistor 

should be reasonable for the site and time of year 

and match the water temperature measured and noted 

on the field form. Speed-of-sound calculations that 

are not corrected for temperature can cause velocitymeasurement errors and depth errors as great as 7 

percent. An error in temperature caused by a faulty 

ADCP thermistor results in an erroneous calculation 

of water density and introduces uncertainty into the 

speed-of-sound calculations (Simpson, 2002).

6. The salinity of the water at the measurement site 

should be measured and noted on the field form 

and entered into the ADCP software for use in the 

speed-of-sound calculations. If the hydrographer has 

entered an incorrect salinity value or has forgotten to 

enter the proper value, depths and velocities will be 

calculated incorrectly. Errors in excess of 3 percent 

can be caused by speed-of-sound calculations that 

are not corrected for salinity (Simpson, 2002).

7. A moving-bed test using proper technique should 

be performed prior to the discharge measurement, 

recorded, archived, and noted on the ADCP measurement field note forms. If a moving bed was 

detected, GPS should be used. If GPS was not used, 

the measured discharges should be adjusted for the 

moving bed (Appendix B).

8. The average boat speed for the measurement should 

not have exceeded the average water speed unless it 

was impractical or unsafe to do so. The reason for 

any exceedance should be documented in the field 

notes or station file. Boat pitch-and-roll should not 

be excessive. Excessive boat speed or pitch-and-roll 

may justify downgrading the measurement quality.

9. The measured edge distances recorded on the ADCP 

measurement field form should match those electronically logged with each transect. The correct 

edge shape should be selected and 5–10 seconds of 

data collected at transect stop and start points while 

the boat is held stationary. If subsectioning was used 

to correct problems with edges, then the reason for 

subsectioning should be clearly documented on the 

field forms. If a vertical wall is present, then the start 

and end points for the transect should be located 

such that the distance from the wall is equivalent to 

or greater than the water depth at the wall.

10. The number of missing or invalid ensembles should 

not be excessive. (An ensemble is a single profile of 

the water velocity through the water column consisting of one or the mean of multiple pings.) The 

number of missing or invalid ensembles that will 

result in a poor measurement is difficult to establish 

because the location and clustering of the missing or 

invalid ensembles is important. If 50 percent of the 

ensembles were missing or invalid, but every other 

ensemble was valid, the measurement could still 

be a good measurement. However, if 10 percent of 

the ensembles were missing or invalid, but they all 

occurred in one location where the neighboring valid 

data would be a poor representation of what was 

unmeasured, the measurement would be poor. When 

the missing or invalid ensembles always occur in 
Office Procedures 27

the same part of the cross section, and the percentage of flow that is likely unmeasured and, therefore, 

estimated for missing or invalid ensembles exceeds 

5 percent, the measurement quality should be downgraded or the transect determined to be unacceptable.

11. The criteria for invalid depth cells are similar to 

those for missing or invalid ensembles. Degrading 

the measurement is not necessary if the distribution 

of the invalid depth cells is fairly uniform throughout the water column or the measured cross section. 

However, significant unmeasured portions of the 

section due to one or more clusters of invalid depth 

cells can be a reason to downgrade the measurement 

quality or deem the transect unacceptable.

12. The extrapolation method for the top and bottom 

discharges should be reviewed. If review of the data 

shows the need for a different extrapolation method 

than that chosen for use in the field, the extrapolation method should be corrected and the reasons 

documented on or attached to the measurement 

field form. Wind and horizontally stratified density 

currents are common causes for profiles that poorly 

fit the one-sixth power-law extrapolation method. In 

these situations, it is usually necessary to use different extrapolation techniques for the top and bottom 

areas and(or) to limit the portion of the profile used 

for the selected method. 

a. RiverSurveyor software allows the user to 

determine which portions of the profile are used 

to estimate the top and bottom unmeasured 

areas using either a constant or one-sixth 

power-law method. For irregular profiles, 

adjusting the number of points used for the top 

or bottom extrapolation can provide a better 

estimate of the unmeasured discharge. 

b. WinRiver software provides different options 

for the top and bottom extrapolation. The threepoint slope method for top extrapolation uses 

the top three depth cells to estimate a slope, and 

this slope is then applied from the top depth 

cell to the water surface; however, a constant 

value or slope of zero is assumed if less than 

six depth cells are present in the profile. The 

velocity must go to zero at the streambed, and 

this is often referred to as a “no-slip” condition 

in fluid mechanics. The no-slip method for 

bottom extrapolation uses the depth cells 

present in the lower 20 percent of the depth to 

determine a power fit forcing it to zero at the 

bed. In the absence of any depth cells in the 

lower 20 percent, the no-slip method uses the 

last single valid depth cell and forces the power 

fit through it to be zero at the bed. It is important to also note that the bottom extrapolation 

method chosen by the user determines how 

missing depth cells in the center of the profile 

are estimated. If the power fit is used at the 

bottom, the velocities for the invalid depth cells 

are interpolated using the power fit through all 

of the data. If the bottom extrapolation method 

is set to no slip, a linear interpolation method is 

used to fill in invalid data. 

13. Measurement computations, including mean discharge and measurement gage height, must 

be correct. 

Problems identified during the review process should be 

viewed as an opportunity for improving future measurements. 

If the measurement section had undesirable characteristics 

(undesirable measurement section characteristics are described 

in the Site Selection section of this report), future measurements should be made at a more appropriate measurement 

section. If boat operation technique problems are identified, 

these problems should be discussed with the boat operator 

so they are not repeated during future measurements. If the 

ADCP and the data-collection software could have been more 

accurately configured, this problem also should be discussed 

with the field crew. A step-by-step measurement review 

process is summarized in Appendix F – Measurement 

Review Procedures.

Data-Quality Indicators

Data-quality indicators for ADCP discharge measurements are not only valuable in the office during measurement 

processing but also are helpful in the field for selecting 

measurement sites and identifying problems and making 

necessary adjustments while data are being collected. Possible 

data-quality indicators follow.

•	 Numerous missing ensembles indicate communication 

problems between the ADCP and the computer. The 

computer may not be able to keep up with the incoming data or may have gone to sleep and missed incoming data. Power to the ADCP may have been interrupted or the communications cable may not have been 

attached securely. Missing data cannot be recovered.

•	 Numerous invalid ensembles indicate that the ADCP 

frequently was unable to measure the velocities in a 

portion of the cross section (figs. 13 and 14). For an 

invalid ensemble, the software receives all of the data 

from the ADCP, but the data do not meet the criteria 

for a valid velocity measurement. Invalid ensembles 

can be caused by (a) invalid bottom tracking, which 

would provide no boat reference from which to 

compute the velocity, (b) decorrelation of the acoustic 

pulse (from turbulence, high shear, submerged debris, 

or fish), which would not permit an accurate measurement of the Doppler shift, (c) low backscatter, which 
28 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

results in an insufficient amount of acoustic energy 

reflected back to the transducer to allow the ADCP to 

measure the Doppler shift, (d) the blocking of acoustic 

pulses by air entrainment, or (e) user-specified dataquality criteria. 

•	 Ambiguity errors in velocity measurements will show 

up as velocity spikes when compared with the neighboring valid velocity measurements (fig. 15). Typically, 

this is only a problem for broadband instruments and 

can be filtered out in post processing.

•	 Beam intensities should be consistent throughout the 

water column down to the streambed, at which point 

a relatively large intensity should be evident because 

the bottom is a much better reflector of acoustic energy 

than scatterers in the water. Anomalies in beam intensities through the water column can indicate interference 

from side walls, fish, trees, or other submerged debris 

that can degrade the quality of the velocity measurement (figs. 16 and 17). 

Figure 13. Screen capture from Teledyne RD Instruments WinRiver software illustrating numerous invalid ensembles 

collected in the Pigeon River at Canton, North Carolina, as a result of invalid bottom tracking.

Figure 14. Screen capture from Sontek/YSI RiverSurveyor software illustrating numerous invalid ensembles in the 

thalweg of the Mississippi River at Chester, Illinois, as a result of invalid bottom tracking.
Office Procedures 29

Figure 15. Screen capture from Teledyne RD Instruments WinRiver software 

illustrating erroneous velocity measurements caused by ambiguity errors.

Figure 16. Screen capture from Sontek/YSI RiverSurveyor software illustrating 

an example of good and bad beam intensity data relative to detection of the 

streambed.

Good Intensity 

Plot

Streambed is not detected

Bad Intensity

Plot

Streambed

•	 Irregular or erratic boat motion creates rapid horizontal accelerations 

of the ADCP, which leads to noisy 

boat velocity measurements and in 

turn can degrade the accuracy of the 

water-velocity measurement. The most 

common cause of irregular or erratic 

boat motion is shifting the boat in and 

out of gear frequently (fig. 18). The 

consistency of boat speed throughout 

a cross section is most evident in the 

time series plot of water and boat 

speed (figs. 18 and 19). 

•	 Rapid variation in the pitch-and-roll 

time series plots indicate that the 

ADCP is measuring in rough, turbulent conditions or that there is significant movement of people or equipment in the boat deploying the ADCP. 

Inconsistent pitch-and-roll throughout 

an ADCP measurement can lead to 

decorrelation of the acoustic signal and result in numerous invalid 

ensembles (unmeasured sections of the 

channel).
30 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Figure 17. Screen 

capture from Teledyne 

RD Instruments WinRiver 

software illustrating an 

anomaly in beam intensities 

caused by interference in 

beam 1 from a side wall.

Figure 18. Screen capture from Teledyne RD Instruments WinRiver software illustrating highly variable boat speeds 

resulting from shifting the motor in and out of gear while measuring along the transect (red line–water speed; green 

line–boat speed).

Figure 19. Screen capture from Sontek/YSI RiverSurveyor software illustrating variation in boat speed while 

measuring along a transect.

0.0

0.1

0.2

0.3

Bs(m/s)

20 40 60

Profile #

0.0

0.1

0.2

0.3

Bs(m/s)

20 40 60

Profile #
Office Procedures 31

•	 Irregularities in bottom-tracking depth measurements 

will lead to spikes in the streambed profile (fig. 20), 

which can influence the accuracy of measured discharge by biasing the measured cross-sectional area. 

The depth used for discharge computations is an 

average of the depths measured for each of the ADCP 

beams. If one or more of the beams strikes an object 

such as a fish, a submerged tree, or debris, before 

reflecting off the streambed, or if the ADCP processes 

a multiple-return of the bottom acoustic pulse, the 

recorded depth for that section and therefore the crosssectional area will be biased. Post-processing datascreening functions in the software can smooth these 

spikes in bottom depth. 

•	 When using the GGA output string from GPS as a 

boat-speed reference, the quality of the differentially 

corrected global positioning system (DGPS) signal 

influences the measurement of ADCP movement, 

which directly affects the quality of the water-velocity 

measurement by the ADCP (fig. 21). The integration 

of a DGPS to track the movement of the ADCP can 

be used to avoid the systematic bias associated with a 

moving bed. DGPS systems, however, cannot always 

provide consistently accurate positions because of 

multipath errors, changes in viewable satellites, and 

satellite signal reception problems on waterways with 

dense tree canopy along the banks, in deep valleys 

or canyons, and near bridges. Hydrographers should 

monitor the DGPS quality-assurance tabular summaries provided in ADCP software to assure that the 

DGPS signal is not affected by these errors during data 

collection.

Figure 20. Screen capture from Teledyne RD Instruments WinRiver software illustrating spikes in the streambed 

profile.
32 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Commonly Observed Measurement Problems

In-depth reviews of acoustic programs at USGS offices 

indicate that the most common problems related to ADCP data 

quality include the following:

1. No moving-bed test conducted or documented;

2. Discharge measurements not adjusted or downgraded correctly when a moving-bed condition is 

present;

3. Selection of a cross section with site conditions that 

are not appropriate for the ADCP;

4. The instrument mode that is most applicable to site 

conditions is not used;

5. Excessive boat velocity (appreciably greater than the 

mean water velocity);

6. Edge distances estimated, not measured;

7. Poor data-archival procedures;

8. Incorrect extrapolation methods for profile shape;

9. No ADCP diagnostic test;

10. ADCP time not properly set;

11. Poor field notes; and

12. ADCP depth not measured or incorrectly assigned.

ADCP users should pay special attention to these problems 

when planning ADCP data-collection efforts, collecting data, 

processing and archiving data, and developing office qualityassurance plans (Oberg and others, 2005). 

Selected References

Callede, J., Kosuth, P., Guyot, J.L., and Guimaraes, V.S., 

2000, Discharge determination by acoustic Doppler current 

profilers (ADCP): A moving bottom error correction 

method and its application on the River Amazon at Obidos: 

Hydrological Sciences-Journal-des Sciences Hydrologiques, 

v. 45, no. 6, p. 911–924.

Chen, Cheng-Lung, 1989, Power law of flow resistance in 

open channels—Manning’s formula revisited: Proceedings 

of the International Conference on Channel Flow and 

Catchment Runoff, Centennial of Manning’s Formula and 

Kuichling’s Rational Formula, May 22–26, 1989, Charlottesville, VA, v. 8, p. 17–48.

Christensen, J.L., and Herrick, L.E., 1982, Mississippi River 

test, volume 1. Final report DCP4400/300, prepared for the 

U.S. Geological Survey by AMETEK/Straza Division, El 

Cajon, California, under contract No. 14–08–001–19003, 

p. A5–A10.

Doppler, J.C., 1842, Über das farbige Licht der Doppelsterne 

und einiger anderer Gestirne des Himmels: Abn.königl.

böhm.Ges.Wiss, v. 2, p. 465–482.

Figure 21. Screen capture from Sontek/YSI RiverSurveyor software illustrating 

the effects of poor GPS data on the measurement of boat movement.

Erroneous boat path 

resulting from bad 

GPS data
Selected References 33

Environment Canada, 2004, Procedures for conducting ADCP 

discharge measurements: Water Survey of Canada, Hydrometric Operations Division, SOP001–2004.

Federal Aviation Administration, 2006, WAAS and its 

relation to enabled hand-held GPS receivers, accessed 

September 22, 2008, at http://gpsinformation.net/exe/waas.

html

Fulford, J.M., and Sauer, V.B., 1986, Comparison of velocity interpolation methods for computing open-channel 

discharge in Subitsky, S.Y., ed., Selected papers in the 

hydrologic sciences: U.S. Geological Survey Water-Supply 

Paper 2290, 154 p.

García, C.M., Oberg, K., and García, M.H., 2007, ADCP 

measurements of gravity currents in the Chicago River, 

Illinois: Journal of Hydraulic Engineering, v. 133, no. 12, 

p. 1356–1366.

Huang, Hening, 2000, Principle and accuracy analysis of 

river discharge measurement using SonTek RiverSurveyor 

System: San Diego, CA, SonTek/YSI, 11 p.

Lipscomb, S.W., 1995, Quality assurance plan for discharge 

measurements using broad-band acoustic Doppler profilers: 

U.S. Geological Survey Open-File Report 95–701, 7 p.

Mathworks, Inc., 2005, Matlab—The language of technical 

computing: Natick, MA, Mathworks, Inc., v. 7.1.

Morlock, S.E., Nguyen, H.T., and Ross, J.H., 2002, Feasibility 

of acoustic Doppler velocity meters for the production 

of discharge records from the U.S. Geological Survey 

streamflow-gaging stations: U.S. Geological Survey WaterResources Investigations Report 01–4157, 59 p.

Mueller, D.S., 2002, Use of acoustic Doppler instruments for 

measuring discharge in streams with appreciable sediment 

transport, in Conference of Hydraulic Measurements and 

Experimental Methods, Estes Park, CO, 2002, Proceedings: Environmental and Water Resources Institute of the 

American Society of Civil Engineers.

Mueller, D.S., Abad, J.D., García, C.M., Gartner, J.W., 

García, M.H., and Oberg, K.A., 2007, Errors in acoustic 

Doppler profiler velocity measurements caused by flow 

disturbance: Journal of Hydraulic Engineering, v. 133, 

no. 12, p. 1411–1420.

Mueller, D.S., and Wagner, C.R., 2006, Application of the 

loop method for correcting acoustic Doppler current profiler 

discharge measurements biased by sediment transport: 

U.S. Geological Survey Scientific Investigations Report 

2006–5079, 26 p.

National Marine Electronics Association, 2002, NMEA 0183 

Standard for interfacing marine electronic devices, version 

3.01: National Marine Electronics Association.

Oberg, K.A., 2002, In search of easy-to-use methods for 

calibrating ADCPs for velocity and discharge methods, in

Wahl, T.L., Pugh, C.A., Oberg, K.A., and Vermeyen, T.B., 

eds., 2002, Hydraulic measurements and experimental 

methods 2002: Proceedings, Conference of Environmental 

and Water Resources Institute of the American Society of 

Civil Engineers, July 28–August 1, 2002, Estes Park, CO.

Oberg, K.A., Morlock, S.E., and Caldwell, W.S., 2005, 

Quality-assurance plan for discharge measurements using 

acoustic Doppler current profilers: U.S. Geological Survey 

Scientific Investigations Report 2005–5183, 35 p.

Oberg, K.A., and Mueller, D.S., 2007a, Analysis of exposure 

time on streamflow measurements made with acoustic 

Doppler current profilers, in Proceedings of the Hydraulic 

Measurements and Experimental Methods 2007, Reston, 

VA, American Society of Civil Engineers. 

Oberg, K.A., and Mueller, D.S., 2007b, Validation of streamflow measurements made with acoustic Doppler current 

profilers: Journal of Hydraulic Engineering, v. 133, no. 12, 

p. 1421–1432.

Ott, Lyman, 1988, An introduction to statistical methods and 

data analysis: Boston, PWS-KENT Publishing Company, 

945 p.

Rantz, S.E., and others, 1982, Measurement and computation 

of streamflow, volume 1, Measurement of discharge: U.S. 

Geological Survey Water-Supply Paper 2175, 631 p.

Rehmel, M.S., Stewart, J.A., and Morlock, S.E., 2002, 

Unmanned, tethered acoustic Doppler current profiler 

platforms for measuring streamflow: U.S. Geological 

Survey Open-File Report 03-237, 15 p., accessed 

September 22, 2008, at http://hydroacoustics.usgs.gov/

publications/rehmel_teth_dop.pdf

Ruhl, C.A., and Simpson, M.R., 2005, Computation of 

discharge using the index-velocity method in tidally affected 

areas: U.S. Geological Survey Scientific Investigations 

Report 2005–5004, 41 p.

Schlichting, H., 1979, Boundary layer theory (7th ed.): New 

York, McGraw-Hill.

Simpson, M.R., 2002, Discharge measurements using a broadband acoustic Doppler current profiler: U.S. Geological 

Survey Open-File Report 01–01, 123 p., accessed June 22, 

2007, at http://pubs.usgs.gov/of/2001/ofr0101/

Simpson, M.R., and Oltmann, R.N., 1993, Discharge measurement using an acoustic Doppler current profiler: U.S. 

Geological Survey Water-Supply Paper 2395, 34 p.

SonTek/YSI, 2000, Acoustic Doppler profiler principles of 

operation: San Diego, CA, SonTek/YSI, 28 p.
34 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

SonTek/YSI, 2007, RiverSurveyor system manual, software 

version 4.60: San Diego, CA, SonTek/YSI, 194 p.

Teledyne RD Instruments, 1996, Principals of operation—A 

practical primer for broadband acoustic Doppler current 

profilers (2d ed.): San Diego, CA, Teledyne RD Instruments, 51 p.

Teledyne RD Instruments, 2003, WinRiver user’s guide—

USGS version: San Diego, CA, Teledyne RD Instruments, 

P/N 957–6096–00, 156 p.

Teledyne RD Instruments, 2006, WinRiver II quick start 

guide: San Diego, CA, Teledyne RD Instruments, P/N 

957–6230–00, 37 p.

Teledyne RD Instruments, 2007, WinRiver II user’s guide: San 

Diego, Teledyne RD Instruments, CA, P/N 957–6231–00, 

166 p.

Teledyne RD Instruments, 2008, Workhorse Rio Grande 

ADCP, accessed December 15, 2008, at http://www.

rdinstruments.com/datasheets/rio_grande_ds_lr.pdf

Urick, R.J., 1983, Principles of underwater sound (3d ed.): 

New York, McGraw-Hill, 423 p.

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manual on hydrographic surveying (EM 11103–2–1003), 

accessed August 24, 2006, at http://www.usace.army.mil/

inet/usace-docs/eng-manuals/em1110-2-1003/toc.htm

U.S. Geological Survey, 2002a, Configuration of acoustic 

profilers (RD Instruments) for measurement of streamflow: 

U.S. Geological Survey, Office of Surface Water Technical 

Memorandum 2002.01, accessed August 13, 2008, at 

http://hydroacoustics.usgs.gov/memos/OSW2002-01.pdf

U.S. Geological Survey, 2002b, Policy and technical guidance 

on discharge measurements using acoustic Doppler current 

profilers: U.S. Geological Survey, Office of Surface Water 

Technical Memorandum 2002.02, accessed August 13, 

2008, at http://hydroacoustics.usgs.gov/memos/OSW2002-

02.pdf

U.S. Geological Survey, 2003, Release of WinRiver software 

version 10.05 for computing streamflow from acoustic 

profiler data: U.S. Geological Survey, Office of Surface 

Water Technical Memorandum 2003.04, accessed July 21, 

2008, at http://hydroacoustics.usgs.gov/memos/OSW2003-

04.pdf

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Office of Surface Water Technical Memorandum 2005.08, 

accessed August 13, 2008, at http://hydroacoustics.usgs.

gov/memos/OSW2005-08.pdf

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Instruments StreamPro acoustic Doppler profiler: U.S. 

Geological Survey, Office of Surface Water Technical 

Memorandum 2005.05, accessed August 13, 2008, at http://

hydroacoustics.usgs.gov/memos/OSW2005-05.pdf
Appendix A – Basic ADCP Operational Concepts 35

Appendix A – Basic ADCP 

Operational Concepts

Descriptions of how an ADCP operates and measures 

water and boat velocity can be found in reports produced 

by ADCP manufacturers (SonTek/YSI, 2000; Teledyne RD 

Instruments, 1996), by the USGS (Simpson, 2002), and by 

others not referenced herein. This appendix is not intended 

to be a comprehensive coverage of information that can be 

found in other documents, but rather a concise overview of 

key operation concepts that will help the user understand the 

capabilities and limitations of ADCPs.

General

The ADCP transmits acoustic energy at a known frequency and measures the change in frequency of the acoustic 

energy reflected back (backscattered) from particles in the 

water column. The velocity of the water along the acoustic 

path can be computed from equation A1.

, 2

D

S

CF

V

F =

where

V is the velocity of the water parallel to the 

acoustic path;

C is the speed of sound in the water;

FD is the difference in frequency due to the 

Doppler shift (FB–FS);

FS is the frequency of the transmitted acoustic 

energy; and

FB is the frequency of the backscattered acoustic 

energy.

The success of the Doppler approach to measuring water 

velocity rests on the assumption that a sufficient amount of 

material is in the water column to reflect enough acoustic 

energy to allow the measurement of the Doppler shift and that 

the material is traveling at the same velocity as the water. If an 

object in the water column is large relative to the suspended 

material and has a velocity that is not dependent on the water 

velocity (such as fish or woody debris lodged on bottom) 

the acoustic energy reflected from this object will not have a 

Doppler shift that reflects the water velocity and will likely 

corrupt the velocity profile at and below the depth of the 

object. Most instruments contain algorithms to detect and filter 

out data with these types of errors.

Measuring Velocity

Currently (2008) the two techniques commonly used in 

an ADCP to measure the Doppler shift can be classified as 

narrowband or broadband. Each approach has its advantages 

and disadvantages. A detailed explanation of each technique 

is beyond the scope of this report, and some of the specifics 

of their implementation into commercial instruments are 

considered proprietary. The basics of the two approaches, 

however, are described using an analogy developed by Joel 

Gast (Teledyne RD Instruments, oral commun., 1992) and 

published by Simpson (2002).

Narrowband

Consider a freeway at night with traffic moving at a 

steady rate of speed. A camera has been placed near the 

freeway, and posts have been installed at set distances within 

the camera’s field of view. A strobe light is actuated and, 

while the freeway is illuminated by the single-strobe pulse, 

the camera takes two high-speed photographs. An investigator examines the photographic negatives and lines up the 

images of the cars on the two photographic negatives. The 

investigator then determines the distance traveled by the cars 

by measuring the apparent shift in position of the reference 

posts (fig. A-1). The speed of the cars can be calculated by 

dividing distance between the posts by the lag time between 

the two photographs. If the strobe flashes represent acoustic 

pulses, the cars represent reflective particles in the water 

column, and the photographic negatives represent the received 

reflected signals, this scenario becomes roughly analogous to 

the workings of a narrowband ADCP system. 

The drawback to this approach is that the strobe (pulse 

length) dissipates very quickly and the two photographs must 

be taken while the same cars are still illuminated by the strobe. 

This means that time lag between negatives (received signals) 

is very short and the distance traveled by the cars (reflectors) 

is very short; therefore, the car speeds cannot be measured 

precisely. Because of these limitations, velocity measurements 

Figure A-1. Freeway strobe-light system used to measure 

vehicle speed (from Simpson and Oltmann, 1993).

(A1)
36 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

made using the narrowband technology are “noisy,” which 

means they have a relatively high random error. The signal 

is sampled twice during the reception of the reflected signal. 

Using an autocorrelation technique, the Doppler shift is then 

calculated. In the narrowband ADCP, the pulse length depends 

on the time lag between samples, which is a function of depthcell size. A filter scheme that looks at the whole returned 

signal is used to resolve ambiguity.

The high random errors of the narrowband system are 

overcome by averaging. The standard deviation of random 

noise about a true mean is reduced by the square root of the 

number of measurements used to computed the mean (Ott, 

1988). The narrowband ping is simple and can be processed 

quickly. Current (2008) narrowband systems can ping at 

rates up to 20 Hz. By pinging fast and averaging the velocity 

measurement of each ping, a narrowband ADCP can measure 

water velocity with random noise standard deviations of 

between 0.4 ft/s and 1 ft/s for 1-second averaging and between 

0.16 ft/s and 0.43 ft/s for commonly used 5-second averages.

Broadband

Using the same freeway analogy as before, the investigator installs another camera a distance of 10 or more car lengths 

(parallel to the freeway) from the first camera. He can now 

actuate a strobe, take a picture with the first camera, wait a 

short time, actuate another strobe, and take a picture with the 

second camera. If the strobes are timed correctly, the cars will 

travel from the field of view of the first camera into the field of 

view of the second camera during the time between photographs. The investigator synchronizes the positions of the cars 

on the two negatives and finds that there is a much longer lag 

time (time between each strobe versus the time between two 

photographs taken during the same strobe) and that the cars 

traveled a longer distance. This longer distance of travel and 

lag time allows the investigator to calculate the speed of the 

cars with much greater precision than with the single-strobe 

system. However, the distance between the cameras and the 

time between each strobe must be chosen carefully. If the 

investigator waits too long between strobes, random movement between the cars (passing, slowing down, speeding up, 

and so forth) will render the two negatives “unmatchable” 

(uncorrelated). Transmitting a pair of pulses (strobes) into the 

water allows for much longer lag times (therefore, more precision) than the narrowband system, but some disadvantages are 

associated with this technique.

One of the most significant disadvantages is self noise. 

Self noise again can be described using the freeway analogy. Suppose that, because of limitations in photographic 

technology, the freeway cameras have no shutters. Because 

the investigator must leave the camera shutters open, both 

cameras will “see” the traffic illuminated by the two strobes. 

However, only 50 percent of the “scenery” will be usable to 

both cameras for correlation purposes. For example, the film 

in camera one is exposed once during the first strobe. The cars 

then travel out of the field of view of camera one and into the 

field of view of camera two. However, the film in camera two 

already has been exposed by the flash of the first strobe and, 

thus, any cars photographed have left the field of vision. When 

the second strobe flashes, the film in both cameras is again 

exposed (double exposed) and the cars that were first photographed by camera one are now photographed by camera two. 

Because the film has been double exposed, only 50 percent of 

the scenery in each exposure contains cars that are common 

to both cameras. As in the film of the freeway cameras, the 

reflected wave front from the first broadband ADCP (BBADCP) pulse-pair is again “exposed” by the incident wave 

front of the second pulse and, therefore, is subject to the same 

“double exposure.” The increased noise due to this 50-percent 

correlation is reduced by data averaging (very narrow pulses 

can be used, and, therefore, large amounts of data can be 

collected and averaged). Without a technique called phase 

coding and a high signal-processing rate, BB-ADCP velocity 

measurements would be less precise (because of self noise) 

than measurements made by the narrowband ADCP system.

The broadband approach makes use of very narrow 

(short) pulses. If these pulses were so narrow that 100 of 

them could be placed into the space occupied by the original 

long pulses, the measurement precision would be increased 

by the square root of the number of samples (in the case of 

100 samples, by a factor of 10). With this increased precision 

(even with the 50-percent level of self noise), the broadbandADCP measurement precision surpasses the precision of 

the narrowband ADCP by almost one order of magnitude. 

However, energy loss caused by the narrow pulses is so great 

that it renders the system nearly unusable. To overcome this 

energy loss, the manufacturer developed a design innovation 

that incorporates most of the advantages of wide and narrow 

pulses. A wide pulse is transmitted (therefore, delivering more 

energy into the water than a narrow pulse), but is logically 

split into many small segments called code elements, each 

having a phase shift of either 0 or 180 degrees (fig. A-2). The 

coding order of these phase shifts is pseudorandom (behaves 

numerically like a random sequence). The consequence of 

transmitting this phase-coded pulse-pair series into the water is 

that even though the pulses are long, the signal processor still 

Figure A-2. Acoustic pulses for narrowband and broadband 

ADCP technologies.

Code Element

Narrowband Monochromatic Acoustic Pulse

Broadband Coded Acoustic Pulse
Appendix A – Basic ADCP Operational Concepts 37

must wait the full lag period before achieving an autocorrelation peak of significant amplitude. In other words, 

because of the phase coding, it is difficult for the autocorrelation algorithm to realize a peak at the wrong interval. The 

objective of the manufacturer is to achieve decorrelation of 

adjacent pulse pairs and, therefore, a greater effective N (number of samples used for data averaging). This pseudorandom 

code allows many independent samples to be collected from 

a single ping. The principal reason this technique was named 

“broadband” is that the bandwidth of the ADCP was increased 

to accommodate the signal processing of a narrow-pulse pair 

(coded or not). 

Another significant disadvantage for using the increased 

lag spacing available with the broadband ADCPs is velocity 

ambiguity. For this analogy, assume that the distance the cars 

move in the synchronized photographs is measured using an 

electronic wheel, rather than a flat ruler. The process is to push 

a button to zero the wheel, move the wheel along the distance 

to be measured, and then push another button for the number 

of degrees of rotation of the wheel to be reported. By knowing 

the circumference of the wheel and the amount of rotation, 

we can compute the distance measured. This electronic wheel 

does not count the number of rotations; it only measures the 

rotation of the wheel from 0 to 360 degrees. Because the cars 

could move in either direction, the measurement is further 

limited to only half of the wheel, so that half of the wheel 

measures a positive direction and half measures a negative 

direction, say from 0 to 180 degrees for the positive direction 

and from 360 to 180 degrees (0 to –180) for the negative 

direction. This technique works well provided that the relation 

between the car’s speed and lag time between the photographs 

does not result in more movement than can be measured using 

180 degrees of rotation of the wheel. If the lag is too long 

and(or) the cars are traveling too fast, the distance between 

the photographs could result in the distance being longer than 

can be measured by 180 degrees of rotation of the wheel. For 

example, the distance to be measured requires 190 degrees of 

rotation, and based on the established reference, 190 degrees 

would be interpreted as –170 degrees, and the wrong velocity 

in the wrong direction would be computed. When the rotation 

exceeds 180 degrees, the velocity measured is ambiguous. It 

is unkown if the car traveled a distance equal to 190 degrees, 

–170 degrees, or 550 degrees. The “ambiguity velocity” is the 

velocity the cars must achieve before this confusing circumstance happens. If the strobe flashes are temporally close, 

the ambiguity velocity is high (faster than the cars normally 

travel), but measurement precision is lower because the cars 

have traveled a shorter distance between strobe flashes. If the 

time between strobe flashes (lag) is lengthened to improve the 

measurement precision, the ambiguity velocity becomes lower 

and limits the maximum velocity that can be measured. How 

the ambiguity velocity is set or determined in the ADCP is 

dependent on the water or bottom mode used. Different modes 

resolve ambiguity differently (see Appendix C for a discussion 

of water modes).

Computing Velocity in Orthogonal Coordinates

The Doppler shift is directional and can only measure the 

velocity of motion parallel to the acoustic path (radial velocity; fig. A-3). The goal of most engineering applications is to 

have three-dimensional velocity components measured in an 

orthogonal coordinate system. To measure a three-dimensional 

velocity profile requires a minimum of three acoustic beams 

pointed in known directions. The three beams provide three 

velocity vectors that can then be resolved into three orthogonal 

velocity vectors. The beams typically are equally distributed 

around a circular instrument (120-degree spacing) and tilted 

at a known angle, θ, to the vertical. The equations for a typical 

three-beam system with beam 1 pointed downstream are:

where

Vy is the streamwise velocity assuming 

beam 1 is pointed downstream;

Vx is the cross-stream velocity assuming 

beam 1 is pointed downstream;

Vz is the vertical velocity;

B1 is the radial velocity measured in beam 1;

B2 is the radial velocity measured in beam 2;

B3 is the radial velocity measured in beam 3; and

θ is the tilt angle of the beams referenced to 

vertical.

The use of four beams in a Janus configuration also is 

common in ADCPs. The Janus configuration provides some 

reduction in errors caused by pitch-and-roll and random 

1 2 3 (2 ) / (3sin ), V B B B y = − − 

1 2 3 ( ) / (3cos ), V B B B z = + + 

Figure A-3. The horizontal (VH) and vertical velocity (VV) 

components computed from the velocity measured parallel to the 

acoustic path (VB).

(A2)

(A4)

(A3) 3 2 ( ) / ( 3 sin ), and V B B x = − 
38 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

instrument noise for the orthogonal velocity components. The 

following equations are for a typical four-beam system with 

beam 3 pointed forward:

where

Vy is the streamwise velocity assuming beam 3 

is pointed upstream;

Vx is the cross-stream velocity assuming 

beam 3 is pointed upstream;

Vz is the vertical velocity;

B1 is the radial velocity measured in beam 1;

B2 is the radial velocity measured in beam 2;

B3 is the radial velocity measured in beam 3; 

B4 is the radial velocity measured in beam 4; and

θ is the tilt angle of the beams referenced to 

vertical.

The assumption in applying equations A2–A7 is that the flow 

measured in each beam is the same (homogeneous). If the 

flow measured by one beam is different from any of the other 

beams (one beam is measuring in a vortex and the others are 

in the free stream), the basic assumption of these equations is 

violated, and an incorrect velocity will be computed. Therefore, the velocities measured by an ADCP are less certain in 

flow conditions with high and rapid spatial variations.

Four-beam systems have a redundant beam that can 

be used to compute an error velocity. The error velocity is 

computed as the difference between the vertical velocity 

computed by opposing beam pairs (3 and 4 versus 1 and 2). 

Adding the opposing pairs cancels the horizontal velocity and 

leaves only the vertical component.

where u Ve is the unscaled error velocity.

TRDI scales the error velocity so that the standard deviation 

for the error velocity is equal to the standard deviation of the 

horizontal velocity. The equation used to compute the scaled 

error velocity is

where

Verror is the scaled error velocity computed by TRDI 

ADCPs.

Measuring a Velocity Profile

The ADCP profiling capability is accomplished by time 

gating (and sampling) the received acoustic signal at time 

intervals as the acoustic-beam wave vertically traverses the 

water column. The transmitted acoustic pulse travels at the 

speed of sound through the water and is reflected back toward 

the transducer. Acoustic energy reflected from particles 

deeper in the water column takes a longer time to return 

to the transducer than does acoustic energy reflected from 

particles nearer the transducer. By measuring the two-way 

travel time from transmission of the energy to when the energy 

is received, the distance from the transducer from which the 

energy is reflected can be computed. The ADCP transmits 

a ping along each acoustic beam and then time gates the 

reception of the returned echo on each beam into depth cells 

at specified ranges. Speed and direction are then calculated 

(using a center-weighted mean of the velocities measured in 

the depth cell) and assigned to the center of each depth cell 

over the measured vertical.

Computing Discharge

An ADCP deployed on a moving boat can compute the 

discharge in real time while traversing the stream from one 

bank to the other (Simpson and Oltmann, 1993). Unfortunately 

the ADCP is unable to measure the entire water column 

(fig. A-4). Near the water surface, an unmeasured zone is 

associated with immersion of the ADCP into the water, the 

blanking distance is below the transducer where data cannot 

be collected, and an additional unmeasured range is dependent 

on the water-mode configuration and the depth-cell size. 

The ADCP also cannot measure all the way to the streambed 

due to the potential for side-lobe interference. As the ADCP 

approaches a streambank, the depths will eventually get too 

shallow for valid data collection. Therefore, the discharge 

computed by an ADCP is a summation of the measured portion of the cross section and extrapolated discharge estimates 

for unmeasured portions of the cross section at the top, 

bottom, and both banks. The computation of the measured, 

top, and bottom portions of the cross section occur for 

each ensemble, and the discharge for the edges are added 

to the total.

(A5)

(A6)

(A7)

(A8)

(A9)

1 2 3 4

1 2 3 4

2cos 2cos

 ( ) / (2cos ),

u

e

B B B B

V

B B B B

 



+ + = −

= + − −

4 3 ( ) / (2sin ), V B B y = − 

1 2 ( ) / (2sin ), and V B B x = − 

1 2 3 4 ( ) / (4cos ), V B B B B z = + + + 

[ 1 2 3 4 ]

1 2 3 4

( ) / (2cos ) 1/ ( 2tan )

 ( ) / 2 2 sin )

V B B B B error

B B B B

 



= + − −    

= + − − ,
Appendix A – Basic ADCP Operational Concepts 39

LeftEdge Top Measured Bottom ++++= QQQQQQ RightEdge ,

where

Q is the total discharge;

QLeftEdge is the discharge estimated for the unmeasured 

area near the left bank;

QTop is the discharge estimated for the top 

unmeasured area;

QMeasured is the discharge measured directly by the 

ADCP;

QBottom is the discharge estimated for the bottom 

unmeasured area; and

QRightEdge is the discharge estimated for the unmeasured 

area near the right bank.

The algorithms commonly used to compute discharge in each 

portion of the cross section are presented below.

Measured Discharge

Traditional point-velocity meters (Rantz and others, 

1982) compute discharge as the product of the cross-sectional 

area and the mean water velocity perpendicular to the crosssectional area. 

= VAQ

where

A is the cross-sectional area, and

V is the mean water velocity perpendicular to 

the cross-sectional area.

The ADCP discharge computation algorithm is based on this 

same principle. Figure A-5 illustrates the water and 

boat velocity vectors for a single depth cell in an ADCP 

Figure A-4. Acoustic Doppler current profiler beam pattern and locations of unmeasured 

areas in each profile (from Simpson, 2002).

Figure A-5. Boat- and water-velocity vectors for a 

single bin in an ADCP ensemble.

(A10) , (A11)

Distance along the

acoustic wave front

where vertical side lobe

interferes with the main

beam acoustic signal. Side

lobe interference is caused

by the reflection of a vertical

side lobe from the stream bed.

Main beam

(higher sound

intensity)

Side lobe

(lower sound

intensity)

Side lobe

(lower sound intensity)

Profiled

area

Water surface

Transducer depth Transducer

Blanking distance Distance that corresponds to

electronics and transducer

recovery time (after ping)

Area of side lobe

interference
40 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

transect. The cross-sectional area of the depth cell can be computed as the product of the depth-cell size (dz) and ensemble 

width (W). The depth-cell size is defined by the instrument 

configuration. The ensemble width is computed as the product 

of the boat speed and time between ensembles.

A Wdz V dtdz = = b



where

Vb

 is the magnitude of the boat velocity vector, 

and

dt is the time between ensembles.

The discharge for the first ensemble is zero because to 

compute the ensemble width, a time for the previous ensemble 

is needed to compute dt. The water velocity can be computed 

as the product of the magnitude of the water velocity, Vw

 , 

and the unit normal vector of the boat velocity, n



.

The equation for discharge in a depth cell, Qbin , becomes

( ) w b . Q V n V dtdz bin = •   

Applying trigonometric relations, equation A14 can be 

written as

w b sin . Q V V dtdz bin =   

The product of the vector magnitudes and sine of the internal 

angle is defined as the vector cross product, and the equation 

for Qbin can be written in terms of the water- and boatvelocity vector components:

The measured portion of the discharge can then be 

computed as

Top Discharge 

The discharge in the unmeasured zone at the water 

surface must be estimated from the measured data. The length 

of the unmeasured zone at the water surface is determined by 

the draft of the instrument deployment, the blank required to 

avoid the effects of ringing, the water mode configuration, 

and depth-cell size (see the Limitations of ADCPs section for 

a detailed discussion of ringing). The methods for estimating 

the top discharge can be applied to the individual velocity 

components (approach used by SonTek/YSI) or to the cross 

product from equation A16 (approach used by TRDI). Both 

approaches are mathematically identical. For simplicity, only 

the equations using the cross product are shown herein. See 

Huang (2000) for equations based on individual velocity 

components. 

The simplest assumption for estimating the top discharge 

is to assume the velocity (cross product) in the topmost valid 

depth cell is a good estimate of the mean velocity between that 

depth cell and the water surface. This is typically referred to as 

the constant extrapolation method: 

where

 is the velocity cross product, 

zws is the range from the streambed to the water 

surface, and

ztb is the range from the streambed to the top of 

the topmost valid depth cell.

This constant extrapolation method is often used where there 

is an upstream wind or an irregular velocity profile through the 

measured portion of the water column.

A valid but slightly more complicated approach is to 

assume that the water-velocity profile follows a logarithmic 

distribution. Simpson and Oltmann (1993) attempted to 

calculate discharge using several different methods for profile 

estimation (logarithmic and general power law), but found 

that because of “noisiness” of the ADCP-profile data, the 

resulting least-squares-derived estimates were unrealistic, 

especially near the upper part of the profile. A method using 

a one-sixth power law (Chen, 1989) eventually was chosen 

because of its robust noise rejection capability during most 

streamflow conditions. 

where

a is a coefficient derived from a least-squares fit 

of the equation to the measured data,

z is the range from the streambed to the location 

of the value of  , and

b is the exponent commonly assumed to be 1/6.

The power-law estimation scheme is an approximation only 

and emulates a Manning-like vertical distribution of horizontal 

water velocities. Different power coefficients can be used to 

adjust the shape of the curve fit to emulate profiles measured 

in an estuarine environment or in areas that have bedforms that 

produce nonstandard hydrologic conditions. Appling equation 

A19 and integrating to obtain the top discharge estimate yields

( ) ( w b ) . Q V V dtdz V V V V dtdz bin wx by wy bx = × = −  

∑ ∑ = =

=

Ensembles

j

Bins

i

QMeasured Qbin

1 1

b  = za

(A12)

w nVV

  = • (A13)

(A14)

(A15)

(A16)

(A17) .

( ) 1 1

1

,

Ensembles

b b

Top ws tb

j

Q  z z dt + +

=

= ∑ − (A18)

, (A19)
Appendix A – Basic ADCP Operational Concepts 41

( ) 1 1

1

. 1

Ensembles

b b

Top ws tb

j

a Q z z dt

b

+ +

=

= − + ∑

Both SonTek/YSI and TRDI provide additional options 

to estimate the top discharge for nonstandard profiles. SonTek/

YSI allows the user to select the number of depth cells used 

in the top extrapolation method. TRDI restricts the constant 

method to use of the top depth cell only and the power-law 

estimate to using all of the available depth cells, but provides 

an additional 3-point slope method to fit situations where wind 

significantly affects the velocity at the water surface. The 

user is referred to the manufacturer’s documentation for more 

detail on these methods (SonTek/YSI, 2007; Teledyne RD 

Instruments, 2007).

Bottom Discharge

ADCPs cannot measure the water velocity near the 

streambed due to side-lobe interference (see the Limitations 

of ADCPs section for a detailed discussion of side-lobe 

interference). Unlike the top discharge estimation problem 

where the velocity at the water surface is not known, we have 

some understanding of the water velocity at the streambed. 

From fluid mechanics, it is known that the water velocity must 

go to zero at the streambed and that a logarithmic velocity 

profile is a reasonable approximation of the velocity profile in 

the boundary layer (Schlichting, 1979). Therefore, the power 

law is always used to compute the discharge in the bottom 

unmeasured portion of the water column.

where

zbb is the range from the streambed to the bottom 

of the bottom most valid depth cell.

To better apply this method to situations where profile 

throughout the water column may not follow a logarithmic 

distribution, such as for bidirectional flow, SonTek/YSI allows 

the user to select the number of depth cells near the bottom of 

the water column that are used in the least-squares determination of a. TRDI adds an additional method to their software 

called “No-Slip,” which applies equation A21 but restricts the 

least-squares determination of a to depth cells in the bottom 

20 percent of the profile, or in the absence of valid depth cells 

in the bottom 20 percent, the last valid depth cell is used to 

compute a.

Edge Discharge 

The unmeasured discharge at the edges of the stream 

are estimated using a ratio interpolation method presented by 

Fulford and Sauer (1986), which can be used to estimate a 

velocity at an unmeasured location between the riverbank and 

the first or last measured velocity in a cross section (fig. A-6). 

The equation for the estimate is

where

x is a location midway between the riverbank 

and first or last ADCP-measured ensemble 

or L/2,

Vx is the estimated mean velocity at location x ,

Vm is the measured mean velocity at the first or 

last ADCP-measured subsection (fig. A-6),

x d is the depth at location x, and

dm is the depth at the first or last ADCPmeasured ensemble (fig. A-6).

Fulford and Sauer (1986) defined dm and Vm as depth and 

velocity, respectively, at the center of the first or last measured subsection and not the near-shore edge of the ensemble, 

as presented in equation A22. However, because the ADCP 

ensembles purposely are kept very narrow at the start and 

finish of each measurement, the differences between the two 

applications are not significant (Simpson and Oltmann, 1993). 

m

m

x

x

d

V

d

V =

1

1

, 1

Ensembles

b

Bottom bb

j

a Q z dt

b

+

=

= + ∑

Figure A-6. Components used to calculate estimates of 

discharge in the unmeasured edges of cross sections.

(A20)

(A21)

(A22)

L

dm Vm

,
42 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

With the Fulford and Sauer (1986) method, discharge can be 

estimated by assuming a triangular area at the edge as

where

QEdge is the estimated discharge in the unmeasured 

edge,

Aedge is the area of the unmeasured edge,

VL 2/ is the velocity midway between the bank and 

the first or last ADCP-measured ensemble, 

and

L is the distance from the last valid ensemble to 

the edge of water (fig. A-6).

Equation A23 can be written in a more general form, which 

utilizes an edge-shape coefficient.

where

Ce is an edge-shape coefficient.

The edge-shape coefficient can be adjusted by the user to 

reflect unusual edge shapes or roughness but is commonly set 

to 0.3535 for triangular edges and 0.91 for rectangular edges. 

The value for L must be measured and entered by the user (see 

discussion of laser range finders in the Other Equipment section). It is also recommended that 5 to 10 seconds of data be 

collected in a near-stationary position at the beginning and end 

of each transect to obtain a good measurement for Vm and L.

/2

0.5

0.5 0.3535 , m

Edge edge L m m m m

m

d

Q A V Ld V Ld V

d

= = ∗ =

, Q C V Ld Edge e m m = (A24)

(A23)
Appendix B – Collecting Data in Moving-Bed Conditions 43

Appendix B – Collecting Data in 

Moving-Bed Conditions

Cause and Effect of a Moving Bed

To measure absolute water velocities with an ADCP 

(water velocities relative to a fixed reference), the ADCP must 

sense and measure the velocity of the ADCP itself, relative 

to the river bottom. This is referred to as bottom tracking. 

Bottom-tracking measurements are similar to water-velocity 

measurements, but separate acoustic pulses are used. If the 

velocity of the water is known relative to the ADCP (water 

tracking), and the velocity of the ADCP is known relative to 

the river bottom (bottom tracking), then the water velocity 

relative to the bottom can be calculated. However, for the 

calculation of actual water velocities to be accurate, the 

streambed must be stationary. 

The bottom-track pulse often is longer than the watertrack pulse to allow complete ensonification (the filling of 

any fluid medium with acoustic radiation, which is then 

observed and analyzed to study the medium or to locate or 

image objects within it) of the bottom. For the bottom ping to 

accurately measure the depth to and Doppler shift from the 

streambed, the pulse should uniformly ensonify the surface 

of the streambed so that it will receive uniform backscatter. If 

the pulse is too short, the echo returns first from the part of the 

beam closest to the ADCP, followed by successively further 

areas (fig. B-1). The beam angle is different for the near and 

far parts of the beam, making analysis 

of the signal difficult. A pulse ensonifying the entire bottom will produce an 

accurate and stable measurement of the 

velocity of the instrument. However, 

sediment transport on or near the 

streambed can affect the Doppler shift 

of the bottom-tracking pulses and can 

cause a measurement error referred 

to as a moving bed. When the bottom 

is ensonified the sediment above the 

bottom also is ensonified and included 

in the backscattered signal (fig. B-2); 

therefore, the backscattered signal of 

the long pulse may be biased by the 

sediment in the water column just 

above the streambed. In such situations, reflections of bottom-tracking 

pulses from highly concentrated 

near-bed sediments are difficult to 

distinguish from reflections from 

the bed. These near-bed sediments 

typically are being transported in 

the downstream direction. If bottom 

tracking is affected by sediment 

transport, the measured boat velocity 

will be biased in the opposite direction of the sediment 

movement, which would make a stationary boat appear to be 

moving upstream (fig. B-3). Therefore, if sediment moving 

near the streambed is measured by bottom-tracking measurements, the boat will have an apparent upstream velocity, the 

calculated downstream water velocity will be reduced, and the 

corresponding discharge will be biased low.

Determining whether a moving-bed condition exists at a 

site is not always intuitive to a hydrographer because a moving 

bed may be measured by an ADCP even in streams where 

the bed is visually stationary. The detection of a moving bed 

also is dependent upon the frequency of the ADCP. Higher 

frequency ADCPs are more sensitive to sediment transport 

Figure B-1. An example of short and long bottom track 

pulses (from Simpson, 2002).

Figure B-2. An example of the potential for water bias (moving bed) for short and long 

bottom track pulses (from Simpson, 2002).

Long Pulse

Small area illuminated Large area illuminated

Short pulse

near bottom

sediment

suspended

sediment

Bottom

Long backscattered

pulse width

Short backscattered

pulse width

Long Pulse

Small area illuminated Large area illuminated

Short pulse

near bottom

sediment

suspended

sediment

Bottom

Long backscattered

pulse width

Short backscattered

pulse width
44 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

than are lower frequency ADCPs and, therefore, are more 

prone to detecting a moving bed. 

Methods to Identify a Moving Bed

USGS policy (U.S. Geological Survey, 2002b; Oberg and 

others, 2005) requires that a moving-bed test be conducted 

prior to making a discharge measurement. In USGS training 

classes and in Oberg and others (2005), an exception to 

conducting a moving-bed test with every measurement was 

allowed if sufficient documentation was provided in the field 

folder to justify not conducting a moving-bed test. Field 

experience has shown that sediment-transport characteristics 

can vary greatly for the same discharge, depending on 

the hydrograph shape, source of runoff, and season of the 

year. Thus, a moving bed may be detected at a location and 

discharge where one was not previously detected, or a moving 

bed may no longer exist at a location and discharge where 

one previously was detected. Moving-bed conditions also 

have been observed in low-velocity environments (less than 

1 ft/s) and likely are caused by organic material transported 

by the water. To ensure the quality of the data collected, every 

moving-boat measurement made with an ADCP must have 

a recorded moving-bed test. If a site routinely has a moving 

bed and GPS is always used with the ADCP, a moving-bed 

test is still required but need only be 5 minutes in length. This 

requirement supersedes Oberg and others (2005) and various 

USGS training materials.

Stationary Test with No GPS

The first moving-bed-test method requires 

that the boat with the ADCP be held in a stationary 

position while recording ADCP data, using bottom 

tracking as the boat-velocity reference. If the 

stationary position is maintained by a tether or 

anchor so that upstream or downstream movement 

of the ADCP is not possible, the moving-bed test 

should be recorded for no less than 5 minutes; 

however, if the ADCP can move either upstream 

or downstream, such as when the boat operator 

is trying to maintain position of the boat, the test 

should be recorded for no less than 10 minutes. 

These criteria supersede the guidance on stationary moving-bed tests that have been previously 

published in Oberg and others (2005) and U.S. 

Geological Survey (2002b). When a moving-bed 

condition is present, a stationary boat will appear 

to have moved upstream (fig. B-3). The error 

caused by the moving bed can be estimated by 

dividing the distance of the apparent boat motion 

in the upstream direction by the duration of the 

test in seconds. This computation will provide 

the moving-bed velocity detected by the bottom-tracking 

technique. This moving-bed velocity can then be divided 

by the average water velocity from the moving-bed test and 

multiplied by 100 to yield an estimate of the percent bias error 

for a water-velocity measurement at this stream location. In 

the example shown in figure B-3, the distance traveled was 

approximately 360 ft for a 10-minute (600-second) period. 

The estimated moving-bed velocity is 0.59 ft/s. If the mean 

velocity for the discharge measurement was 4.9 ft/s, the 

percent bias error in the water-velocity measurement would 

be estimated to be 12 percent. Criteria for determining if 

a moving bed is present must account for the accuracy of 

the test. If the moving-bed test was completed with a fixed 

tethered deployment, an anchored manned boat, or a manned 

boat where the user is sure there was little movement of the 

boat, a moving bed is determined to be present when the 

measured moving-bed velocity is greater than 1 percent of the 

mean water velocity at the test location. If the moving-bed 

test was made using a manned boat that was not anchored and 

may have moved either upstream of downstream a criteria of 

2 percent instead of 1 percent is used because uncertainty has 

been introduced into the test by boat movement. Dischargemeasurement techniques that are not affected by a moving 

bed, or that correct for the effect of a moving bed, should be 

used if a moving bed has been detected. 

When it is not possible to safely anchor the manned 

boat in the stream because of boat traffic, drift, or other 

hazardous conditions, holding the boat stationary at the 

desired location in the measurement section may be difficult. 

Boat movement in the upstream or downstream direction 

will introduce errors in the moving-bed test when using this 

method. A technique for helping the boat operator determine 

Figure B-3. A moving bed measured with a 1,200-kilohertz acoustic Doppler 

current profiler (ADCP) on the Mississippi River at Chester, Illinois. DISTANCE NORTH, IN FEET

-350 -300 -250 -200 -150 -100 -50 0 50

-50

0

100

50

150

250

200

DISTANCE EAST, IN FEET

End

Start

Ship track

Flow direction
Appendix B – Collecting Data in Moving-Bed Conditions 45

whether the boat is moving excessively in the upstream or 

downstream direction during a moving-bed test is illustrated 

in figure B-4. The boat operator selects two distinguishable 

reference points on shore that are separated by a considerable 

distance from one another (98 ft or more). Examples of distinguishable reference points include telephone or power poles or 

large trees that can be easily distinguished from other nearby 

trees. Bridges, bridge piers, and navigation buoys also can 

be used as reference points for maintaining an approximately 

stationary position when making a moving-bed test. If the boat 

changes position appreciably in the upstream or downstream 

direction, this change should be noted on the field note form, 

and the test should be repeated, if possible. 

The TRDI StreamPro ADCP does not include an internal 

compass. The cross product of the water-velocity and boatvelocity vectors, used for the computation of discharge, does 

not depend on the heading of the instrument (Simpson and 

Oltmann, 1993). However, users began reporting moving-bed 

biases when using the StreamPro where it was apparent 

from the velocity and bed material that little or no sediment 

transport was occurring. The false moving bed observed in 

stationary moving-bed tests conducted with a StreamPro is 

the result of rotation and lateral movement of the StreamPro 

on the end of the tether. During a stationary moving-bed 

test the StreamPro and float often tend to swim or kite from 

the end of the tether. Because the StreamPro does not have 

an internal compass, it cannot compensate for instrument 

rotation. The lack of a compass in a StreamPro does not allow 

the StreamPro to report boat or water velocities referenced to 

a fixed rotational reference, such as magnetic north; rather, the 

StreamPro reports velocities in instrument coordinates. 

Careful analysis of false moving-bed ship tracks indicate 

that ship movement (kiting or swimming) typically is perpendicular to the water velocity. When the StreamPro rotates, the 

boat and water velocities are rotated. Thus, the boat velocity 

and water velocities remain in the correct orientation relative 

to each other. This characteristic permits the discharge to 

be computed without a compass. This characteristic also 

can be used to determine the velocity of the boat in the 

upstream direction. TheBOATvelocity in the upstream direction measured during a stationary moving-bed test can be 

computed using the vector dot product of the boat velocity 

and water velocity. The use of the dot product for analysis of a 

moving-bed test was originally suggested by Randy Marsden 

(Teledyne RD Instruments, oral commun., 

2006). This approach subsequently has been 

developed and applied to the false moving-bed 

problem associated with the StreamPro ADCP. 

The USGS has developed software (Stationary 

Moving-Bed Analysis (SMBA)) that applies 

the dot-product approach and provides a simple 

and efficient user interface to allow users to 

apply the dot-product approach to all StreamPro 

stationary measurements, which has been shown 

to eliminate the effect of the boat/instrument 

motion on the stationary moving-bed test. The 

SMBA program can be obtained from the USGS 

at http://hydroacoustics.usgs.gov/movingboat/

mbd_software.shtml. 

Stationary Test with GPS

A more accurate method for estimating 

the errors introduced by a moving bed can be 

determined if a GPS is available for use and 

is interfaced with the ADCP and the datacollection software. The stationary test with 

GPS method also requires that the ADCP boat 

be held in a stationary position and a data file recorded for at 

least 5 minutes, if GPS data are of good quality. Either bottom 

tracking or GPS can be used for the boat-velocity reference. 

Using GPS as the reference is often easier during data collection so that the boat operator can use the ship-track display 

as a means to assist in holding the boat in an approximately 

stationary position. After the moving-bed test is complete, 

compare the boat track using ADCP bottom track as reference 

with the boat track using GPS as the reference. If the bottomtrack boat velocity data indicate apparent upstream movement 

that the GPS data do not indicate, a moving bed is present. 

The error caused by the moving bed can be computed in the 

same manner as described for the stationary test with no GPS 

method, except that the distance in the upstream direction indicated by bottom tracking should be corrected by the distance 

actually traveled in that direction, as indicated by GPS (Oberg 

and others, 2005). In the WinRiver software, this distance can 

be found in the “compass calibration” tabular window and is 

Figure B-4. Method for verifying that upstream/downstream boat movement is 

minimized during an acoustic Doppler current profiler moving-bed test (modified 

from Environment Canada, 2004).
46 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

labeled “BMG-GMG mag,” and the direction of the “BMGGMG dir” should be in the upstream direction. If the measured 

moving-bed velocity is greater than 1 percent of the mean 

water velocity at the test location, discharge-measurement 

techniques that are not affected by a moving bed, or that 

correct for the effect of a moving bed, should be used.

Loop Method

If the ADCP can be held stationary, stationary 

moving-bed tests are a good measure of the magnitude of an 

apparent moving streambed; however, these tests represent 

moving-bed conditions for only one location in the cross 

section. An alternative to the stationary moving-bed test is 

the loop method, which is based on the fact that as an ADCP 

is moved across the stream, a moving bed will cause the 

bottom-track-based ship track to be distorted in the upstream 

direction. Therefore, if an ADCP makes a two-way crossing 

of a stream (loop) with a moving bed and returns to the exact 

starting position, the bottom-track-based ship track will 

show that the ADCP appears to have returned to a position 

upstream from the original starting position (fig. B-5). The 

mean moving-bed velocity can be estimated from the distance 

the ADCP appeared to have moved upstream from the starting 

position (loop-closure error) and the time required to complete 

the loop.

where 

is the mean moving-bed velocity for the 

measurement section,

Dup is the loop-closure error (distance made good, 

straight-line distance from starting point to 

ending point), and 

T is the measurement time required to complete 

the loop.

These data are readily available from most commercial software used to measure discharge with ADCPs (fig. B-6).

The loop method must be applied properly, or it may 

produce incorrect results. Anyone planning to use the loop 

method should read and follow USGS Scientific Investigations Report 2006–5079 (Mueller and Wagner, 2006), which 

describes the procedures, limitations, and uncertainties 

associated with the loop method. The following steps are for 

collecting and analyzing loop-test data.

1. Calibrate the ADCP/ADP (acoustic Doppler profiler) 

compass using internal calibration routines. A compass 

calibration accuracy of better than 1 degree is desired. 

Calibrations with errors greater than 1 degree should be 

repeated. If a calibration of less than 1 degree cannot be 

obtained after several attempts, appropriate field notes 

should be recorded to document the problem. Compass 

errors greater than 1 degree result in increased errors in 

the loop-method correction.

Figure B-5. A distorted ship track in a loop caused by a 

moving bed.

, up

mb

D

V

T =

Figure B-6. Example of parameters used to compute the mean 

correction for data collected with an ADCP and displayed with 

(A) WinRiver and (B) RiverSurveyor.

(B1)

V mb

DISTANCE NORTH, IN METERS

-100 -50 0 50 100 150

-250

-200

-150

-100

-50

50

0

Dup = Apparent Distance

 Moved Upstream

DISTANCE EAST, IN METERS

(A) (B)
Appendix B – Collecting Data in Moving-Bed Conditions 47

2. Establish a marked starting point where the ADCP/ADP 

can be returned to the exact location. This point is not 

required to be as near to a bank as the end of a regular 

transect. For example, with a tethered boat, controlling 

the boat at the edge of the bank can be difficult because 

of conditions such as slack water, eddies, or vegetation; 

therefore, establishing a point farther out in the flow 

could make navigating the boat back to the starting 

point more practical. Use of a buoy or other fixed object 

is recommended.

3. Make a steady pass back and forth across the stream as a 

normal discharge measurement, but do not stop recording 

at the far bank. At the starting point, make sure the boat 

is ready to begin the transect before beginning to record. 

A uniform boat speed is important. Do not spend extra 

time at the edges. Plan the loop so that a smooth change 

in boat direction can be achieved near the far bank. Too 

much time near the banks will result in a low bias. 

4. Maintain the proper boat speed. The recommended 

maximum boat speed should be the lesser of a boat 

speed that requires no less than 3 minutes to complete 

the loop or a boat speed that is less than 1.5 times the 

mean water speed.

5. Return to the starting point. Accurately returning to the 

starting point is very important.

6. Process the loop file to the end. Record the distance made 

good (DMG) and the time required to complete the loop. 

Note: The DMG in a moving-bed condition should be in 

the upstream direction (fig. B-5). If the primary direction 

of the DMG is in a direction other than upstream, this distance may be the result of compass or bottom-track errors, 

and no moving bed will be assumed.

7. Compute the mean moving-bed velocity.

where

is the mean velocity of the moving bed,

Dup is the DMG, and

T is the measurement time required to complete 

the loop.

8. Compute the ratio of the mean moving-bed velocity to the 

mean water velocity. Note: Because the loop closes on 

itself, the net discharge and cross-sectional area approach 

zero; thus, the mean velocity should be the mean of the 

measured velocities and not the discharge divided by the 

cross-sectional area.

9. Determine if the ratio exceeds the recommended criteria.

In order to minimize the potential error in the measured 

moving-bed bias when using the loop method as a moving-bed test, the hydrographer should use the following 

thresholds in determining and applying a correction for an 

apparent moving streambed.

•	 When using the loop method, a measured mean 

moving-bed velocity of at least 0.04 ft/s indicates the 

presence of a moving bed. 

•	 If the measured moving-bed velocity exceeds 0.04 ft/s, 

the ratio of the mean moving-bed velocity and mean 

water velocity should be computed. 

•	 If this ratio is greater than 0.01, the apparent bed 

movement will cause at least a 1-percent negative 

bias in the computed discharge, and a DGPS or method 

that accounts for or corrects for a moving bed should 

be used. 

Methods to Account for Moving-Bed Effects

The integration of a GPS to measure the velocity of 

the ADCP has been shown to alleviate the systematic errors 

associated with a moving bed (Mueller, 2002) and is the most 

accurate way to measure discharge in moving-bed conditions. 

If, however, a GPS is not available or site conditions do not 

permit its use, methods have been established to correct 

discharge measurements biased by a moving bed. The use 

of a GPS and the application of various discharge correction 

methods are discussed in the following sections.

Using GPS with ADCPs

Using GPS with ADCPs eliminates the effect of a moving 

bed on the velocity measurements but introduces several 

sources of potential error. Understanding how GPS operates 

and how it is used with ADCPs is important for collecting 

high-quality ADCP measurements when using GPS data as the 

boat-velocity reference.

The computation of water velocity from an ADCP 

mounted onto a moving boat is a vector-algebra problem. The 

ADCP measures the water velocity relative to the moving 

boat (relative water velocity), so the velocity of the boat must 

be accounted for to obtain the true water velocity. The true 

water velocity is computed by subtracting the bottom-tracking 

velocity from the water-tracking velocity. When bottom 

tracking is used, the direction of the boat velocity vector as 

measured by bottom tracking (θBT) and water-velocity vector 

(θWT) are referenced to the ADCP (fig. B-7A). The ADCP 

has an internal fluxgate compass to measure the orientation 

of the instrument (θInst) relative to the local ambient magnetic 

field (magnetic north). The water-velocity vector can be easily 

referenced to magnetic north by rotating the vector based on 

the measured θInst and to true north by again rotating the vector 

by a user-specified magnetic variation (θMag). The magnitude 

of the water velocity is unaffected by any errors in the 

V mb

, up

mb

D

V

T = (B2)
48 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

measurement of θInst or entry of θMag when bottom tracking 

is used as the boat-velocity reference. The basic equation 

presented in Simpson and Oltmann (1993) for computing 

measured discharge (exclusive of unmeasured areas) by use of 

an ADCP mounted onto a moving boat is

0 0

sin ,

T D

Q V V dzdt = f b  ∫∫  

where

Q is the total discharge,

T is the total time for which data were collected,

D is the total depth,

Vf

 is the mean water-velocity vector,

Vb

 is the mean boat-velocity vector,

 is the angle between the water-velocity vector 

and the boat-velocity vector (fig. B-7),

dz is the vertical differential depth, and

dt is differential time.

To compute the discharge, only the angle between the watervelocity and the boat-velocity vectors is needed. When GPS 

is used to determine the boat-velocity vector, this vector is 

referenced to true north as determined from the GPS data 

(fig. B-7B). The orientation of the instrument relative to true 

north must be determined to put the boat-velocity vector 

and the relative water-velocity vector in the same coordinate 

system and allow for the computation of the water-velocity 

vector and θ. The discharge is affected by errors in measuring 

θInst and in the determination of the magnetic variation (θMag) 

when GPS is used as the boat reference. The errors associated 

with θInst can cause errors in the measured discharge that are 

proportional to the speed of the boat. Proper setup and calibration of the ADCP’s internal compass, determination of the 

local magnetic variation, and a slow boat speed are critical to 

quality discharge measurements made using GPS data as the 

boat-velocity reference. 

Errors associated with fluxgate-compass measurements 

can result from horizontal accelerations of the ADCP or 

environmental conditions near the instrument. Most fluxgate 

compasses are gimbal-mounted, which allows them to 

measure the Earth’s horizontal magnetic field. When the 

instrument is subject to horizontal accelerations, such as 

when a boat accelerates or turns, the force generated by the 

acceleration causes the compass to swing out of the vertical 

position and measure something other than the horizontal 

magnetic field. Most of the significant errors associated with 

horizontal accelerations can be eliminated by slow, smooth 

boat operation. 

Errors associated with fluxgate-compass measurements 

caused by environmental conditions can be classified as 

Figure B-7. Boat-velocity vectors referenced by (A) bottom tracking and (B) global positioning system 

(adapted from Mueller, 2002).

(B3)

Normal

Vector

True

North Magnetic

North

Orientation

of instrument

Boat-Velocity

Vector

Water-Velocity

Vector

Normal

Vector

True

North Magnetic

North

Orientation

of instrument

Boat-Velocity

Vector

Water-Velocity

Vector

B. Global positioning

 system (GPS)

A. Bottom tracking
Appendix B – Collecting Data in Moving-Bed Conditions 49

one- and two-cycle errors. One-cycle errors are caused by 

permanent magnets and current-carrying conductors; twocycle errors are caused by iron and magnetically permeable 

material. ADCPs manufactured by TRDI and SonTek/YSI for 

making discharge measurements from a moving boat have 

firmware routines to allow the calibration of the compasses in 

place to compensate for environmental conditions. 

The local magnetic variation (or declination) can be 

either estimated or measured, depending upon site conditions. 

Estimates of the local magnetic variation can be obtained from 

USGS 7.5-minute quadrangle maps, magnetic field charts, and 

geomagnetic field models. Although these estimated values 

are often accurate, some areas have appreciable magnetic 

anomalies that are not accurately predicted by models or 

general charts. Teledyne RD Instruments (2003) documents 

a procedure for measuring the magnetic variation onsite by 

use of an ADCP and a DGPS. This same procedure can be 

used with RiverSurveyor instruments and RiverSurveyor 

software from SonTek/YSI. The limitation of this procedure is 

that there can be no moving-bed conditions because both the 

bottom tracking and GPS are used in the computations. 

GPS provides two options for determining boat velocity: 

(1) differentiated position using the GGA NMEA-0183 

sentence and (2) Doppler-based velocity reported in the VTG 

NMEA-0183 sentence. The GGA data sentence broadcast by 

the GPS includes time, positional data (latitude, longitude, and 

elevation), and information about the satellite constellation 

used to reach the position solution. When using the GGA sentence from the GPS to measure the movement of the ADCP, 

the velocity of the instrument is determined by computing the 

distance traveled between successive GPS position solutions 

and dividing that distance by the time between the solutions. 

Hence, positional accuracy is vitally important to achieve 

an accurate measure of ADCP movement using the GGA 

sentence; therefore, a differential correction signal is required. 

To use the GGA sentence, DGPS receivers are required, and 

receivers should have a 95-percent accuracy of about 3.3 ft or 

less in the horizontal location.

Although the differential correction accounts for errors 

induced by the ionosphere, atmosphere, and selective availability, the user must be aware of and take action to minimize 

uncorrectable errors, which can be caused by the user, the 

satellite configuration, or the characteristics of the site. Place 

the GPS antenna as near to the center of the ADCP as possible 

so that the direction of travel is the same for both the antenna 

and the ADCP during all boat maneuvers. The antenna 

should be located above the boat cabin or other accessories 

on the boat to eliminate multipath errors. Multipath errors 

are positional errors that arise when satellite signals bounce 

around before getting to the receiver, rather than taking a 

direct path. The result is a barrage of signals arriving at the 

receiver: first the direct one, then a series of delayed reflected 

ones. This creates a noisy signal, and if the bounced signals 

are strong enough, they can confuse the receiver and cause 

erroneous positional measurements. Sophisticated receivers 

use a variety of signal processing techniques to make sure they 

only consider the earliest arriving signals, which are the direct 

ones. Although these techniques reduce multipath errors, they 

do not completely eliminate the problem.

Occasionally, the configuration of the satellites does 

not allow an accurate determination of the horizontal position. This can be monitored using the horizontal dilution of 

precision (HDOP). If the HDOP parameter is greater than 

2, or if the HDOP changes by more than 1 during a transect, 

the quality of the DGPS positions is suspect. Local site 

characteristics, such as canyon walls, bluffs, tall buildings, 

and tree cover, can result in poor DGPS positions because of 

multipath errors and loss of satellite visibility. Poor satellite 

visibility often results in numerous changes in the number 

and configuration of satellites used to determine a position. 

Numerous changes in satellites are another indication that 

the quality of the DGPS positions may be poor. In addition 

to horizontal-position coordinates, the DGPS also computes 

elevation. This elevation is 2 to 4 times less accurate than the 

horizontal position (Mueller, 2002). The elevation of the boat 

should be reasonably constant. Changes greater than 11.5 ft 

in the DGPS-determined elevation indicate that the quality of 

the DGPS positions may be poor (Teledyne RD Instruments, 

WinRiver 10.06 Help File, written commun., 2006).

While GPS is most often used to determine positions, 

many GPS receivers also can be used to measure velocity 

relative to ground with an assessment of the Doppler shift 

in the satellite carrier phase frequencies, which is typically 

reported in the VTG sentence. The method uses the actual 

signal frequency, and not a phase angle, to determine the 

Doppler shift. No ambiguity can be present in the computed 

velocities. As for the position determination, the velocity 

measurement requires the use of at least four satellites. The 

quality of the solution also is influenced by the number of 

satellites and the shape of the constellation (HDOP) during 

the observation. This alternative has an advantage because it is 

minimally affected by multipath and satellite changes because 

of the short sampling time required. In addition, multipath and 

ionospheric/atmospheric distortions do not affect the precision 

of the measurement. As a result, the Doppler measurement of 

velocity can be produced without the need for any differential 

correction. Emerging research by Environment Canada and 

the USGS using the VTG sentence from a GPS has shown the 

potential to provide better measurements of ADCP movement 

than the GGA data string and without the need for differential 

correction (Francois Rainville, Water Survey of Canada, 

written commun., 2007). Additional research is underway to 

investigate the limitations of the Doppler-derived velocity in 

the VTG sentence.

Alternatives to Using a GPS 

Using a DGPS to measure the velocity of an ADCP has 

been shown to alleviate the systematic errors associated with 

a moving bed (Mueller, 2002). GPS systems, however, do not 

work in all conditions. For example, a GPS will have trouble 

providing consistently accurate positions and velocities on 
50 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

waterways with dense tree canopy along the banks, in deep 

valleys or canyons, and near bridges because of multipath 

and satellite signal reception problems. Alternative methods 

of correcting for the systematic moving-bed error have been 

developed for situations where integrating GPS with an ADCP 

is not possible.

Loop Method

The results of a loop method moving-bed test (previously 

described) can be used to compute the discharge missing from 

the measurement caused by the moving bed. This computed 

missing discharge can be added to the measured discharge to 

yield a corrected discharge. 

, Q Q Q TC TM mb = +

where

QTC is the discharge corrected for the moving-bed 

bias,

QTM is the measured discharge, and

Qmb is the discharge not measured because of the 

moving bed.

A detailed analysis of the application of the loop method was 

conducted by the USGS (Mueller and Wagner, 2006).

Careful field procedures are absolutely critical to the successful application of the loop method. Failure to accurately 

return the instrument to the starting point, an uncalibrated or 

improperly calibrated compass, or loss of bottom track during 

the loop will result in unpredictable errors that render this 

technique unusable. Current research, which is limited by 

the amount of available field data, indicates that site-specific 

characteristics and data-collection techniques, such as the 

shape of the measurement section, distribution of the movingbed velocity, time spent at the banks, boat speed, and uniformity of the boat speed, can affect the discharge correction by 

10 percent or greater. When applied properly, however, this 

technique should consistently yield total corrected discharges 

that are within 5 percent of the actual discharge. The loop 

method cannot be applied with a TRDI StreamPro ADCP 

because it does not have a compass.

After completion of a loop method moving-bed test, 

two methods described by Mueller and Wagner (2006) can 

be used to correct discharge biased by a moving bed—the 

mean correction method and distributed correction method. 

The mean correction method is simple and can be completed 

with manual computations. The distributed correction method 

accounts for the velocity distribution and shape of the cross 

section and requires a computer program.

Mean Correction Method

A simple method for computing the discharge not 

measured because of the moving bed is to compute the mean 

moving-bed velocity and multiply it by the cross-sectional 

area (measured perpendicular to the flow).

mb , Q V A mb =

where

V mb is the mean velocity of the moving bed, and

A is the cross-sectional area perpendicular to the 

mean flow direction.

The mean moving-bed velocity can be computed from the 

distance the ADCP appeared to have moved upstream from the 

starting position (loop-closure error) and the time required to 

complete the loop. These data are readily available from most 

commercial software used to measure discharge with ADCPs. 

The cross-sectional area must be computed perpendicular to 

the mean flow direction. If the cross-sectional area is computed parallel to the ship track measured by the ADCP, then 

the cross-sectional area will be computed based on a ship track 

that is distorted in the upstream direction by the moving bed. 

The distortion of the ship track by a moving bed will result in 

a cross-sectional area that is too large. The mean correction 

method is simple to apply but does not account for the crosssection shape and spatial correlation of the sediment transport 

with the spatial distribution of the discharge in the cross section. Therefore, streams with high spatial variability in sediment transport and discharge distributions may not be properly 

represented by using a single mean moving-bed velocity to 

correct the measured discharge.

Distributed Correction Method

The actual moving-bed velocity at any point in the stream 

is unknown, but the moving-bed velocity is assumed to be proportional to the near-bed water velocity (Callede and others, 

2000). The distributed correction method uses a 1/6th power 

curve to provide a consistent estimate of the near-bed velocity 

at any point in the cross section. To determine the distributed 

loop method correction, the measured mean moving-bed 

velocity from the loop is distributed to each ADCP profile by 

a ratio of near-bed velocity for each profile and the mean nearbed velocity for the cross section. The distributed moving-bed 

velocities are then applied to the water and boat velocities 

for all depth cells in each of the corresponding profiles in 

the measured portion of the cross section to determine the 

corrected measured discharge. The total discharge measured 

by an ADCP consists of a measured portion and estimates of 

discharge in the unmeasured top, bottom, left, and right edges. 

The final corrected measured discharge is computed using the 

ratio of the corrected and uncorrected measured portion of 

the discharge to correct the sum of the measured and top and 

bottom estimated discharges. Water velocities near the bank 

are assumed to be sufficiently low as to not cause a moving 

bed; therefore, no correction is applied to the left and right 

edge discharges. 

Distribution of the mean moving-bed velocity based on 

near-bed velocities requires a consistent method of determining near-bed velocities at each measured vertical. Due to 

(B4)

(B5)
Appendix B – Collecting Data in Moving-Bed Conditions 51

side-lobe interference the lower 6–10 percent, approximately, 

of each velocity profile is unmeasured. In addition, invalid 

velocity measurements are common in the lower portions 

of the profile. Simply using the last valid velocity in each 

measured velocity profile would result in near-bed velocities 

at various distances from the streambed. The 1/6th power law 

has been shown to be consistent with a logarithmic velocity 

profile and is commonly used to estimate the unmeasured 

top and bottom discharges for ADCP measurements (Chen, 

1989; Simpson and Oltmann, 1993). The near-bed velocity 

is computed by fitting the 1/6th power law through zero at 

the bed and through the mean velocity of the last two valid 

velocity measurements in the profile.

The computations associated with the distributed correction are best performed using a computer program. A program, 

LC, has been developed to perform these computations. LC 

reads ASCII files that are readily output by standard vendorsupplied ADCP software, thus allowing all the utilities of the 

data-collection and processing software to be used to validate 

the measured discharge before applying any corrections. The 

LC program prompts the user for the ASCII output filename 

that contains the loop data and computes the magnitude and 

direction of the DMG from the starting and ending points of 

the loop. If the direction of the DMG is +/– 45 degrees from 

the upstream direction and the magnitude is greater than the 

previously stated thresholds for a moving-bed correction, 

then a correction is recommended. The program then reads 

and processes all transects specified by the user and applies 

the method described herein to each transect. The program 

then computes a corrected discharge for each transect and 

the corrected mean discharge for the whole measurement. 

The LC program can be obtained from the USGS at http://

hydroacoustics.usgs.gov/movingboat/mbd_software.shtml.

Multiple Moving-Bed Test Method

The second GPS alternative requires the hydrographer 

to conduct multiple stationary moving-bed tests across the 

stream. The advantages to using the multiple moving-bed 

tests are (1) GPS is not required, (2) no compass calibration is 

required, and (3) the method can be used where bottom track 

cannot be adequately maintained to apply the loop method. 

The disadvantages of this method are (1) multiple moving-bed 

tests are required, (2) ADCP movement is not corrected during 

the moving-bed tests, (3) the procedure is time consuming, 

(4) an accurate cross-sectional area projected perpendicular 

to the mean flow direction is required for all methods except 

when using the Stationary Moving-Bed Analysis (SMBA) 

software, and (5) although the discharges are corrected, 

measured velocities are still uncorrected (biased low).

Field Procedures

1. Conduct at least three stationary moving-bed tests, and 

note the location of each test by measuring the distance 

from shore. Additional moving-bed tests will result in 

a more accurate discharge correction. Be sure to record 

these tests and the locations of each stationary test in the 

cross section.

2. Each moving-bed test should be 5 to 10 minutes in duration. For details, see the Stationary Test with No GPS section under the Methods to Identify a Moving Bed section.

3. Make a typical ADCP discharge measurement.

Processing Procedures

The corrected discharge can be computed from the 

multiple moving-bed tests by using one of three computation 

methods: (1) subsection method, (2) average moving-bed 

velocity method, and (3) distributed method using the 

SMBA software.

Subsection Method

1. Playback each moving-bed test and determine the mean 

moving-bed velocity (V mb) for each section, which can be 

computed from the distance the ADCP appeared to have 

moved upstream from the starting position and the time 

required to make each stationary moving-bed test.

, up

mb

D

V

T =

where

Dup is the DMG in the upstream direction 

(straight-line distance from starting point 

to ending point), and

T is the time required to complete the test.

2. Process the first transect and manually subsection it such 

that the moving-bed tests are located near the middle of 

each subsection.

3. Determine the cross-sectional area perpendicular to the 

mean flow direction (Ai) for each subsection. The crosssectional area will be affected by the moving bed unless 

corrected to be perpendicular to the mean flow direction.

4. Compute the corrected discharge for the transect 

( ), Q Q V A corrected measured = +∑ mbi i

where

 is the moving-bed velocity in the subsection i,

Ai is the cross-sectional area perpendicular to 

flow in subsection i, and 

Qmeasured is the total unadjusted (biased) discharge for 

the transect.

(B6)

(B7)

V mbi
52 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

5. Follow steps 2 through 4 for each transect used during the 

discharge measurement. The mean of the Qcorrected for all 

transects is the corrected discharge for the measurement.

Average Moving-Bed Method

1. As with the subsection method, the first step is to compute the moving-bed velocity for each moving-bed test by 

dividing the DMG by time (eq. B6).

2. Sum the moving-bed velocities for each test and divide 

by two more than the number of moving-bed tests, which 

will account for the absence of a moving bed at both 

edges of water. Therefore, if three moving-bed tests were 

made, the sum of the moving-bed test velocities would be 

divided by 5.

3. The final step is to compute the corrected discharge. 

Calculate the discharge correction by multiplying the 

average moving-bed velocity computed in the previous 

step by the area of the cross section measured perpendicular to the mean flow direction. Then add the discharge 

correction to the measured discharge to determine the 

corrected discharge.

( ), mb Q Q V A corrected measured = + pf

where

Qmeasured is the total unadjusted (biased) discharge for 

the transect,

V mb is the average moving-bed velocity in the 

measurement section (from step 2), and 

Apf is the average cross-sectional area 

perpendicular to flow in the transect. 

Distributed Method using the SMBA Software

The distributed method uses the SMBA computer 

software to automate the correction process for StreamPro 

and Rio Grande ADCPs. The SMBA program can be obtained 

from the USGS at http://hydroacoustics.usgs.gov/movingboat/

mbd_software.shtml. A distributed method similar to that 

used in the loop method (Mueller and Wagner, 2006) was 

developed for multiple moving-bed tests. Instead of using the 

mean moving-bed velocity measured from the loop method, 

the SMBA program distributes the average moving-bed 

velocity from the multiple stationary moving-bed tests to each 

ensemble based on the ratio of near-bed velocity for each 

ensemble and the mean near-bed velocity for the cross section. 

The distributed moving-bed velocities are then applied to 

the water and boat velocities for all depth cells in each of the 

corresponding ensembles in the measured portion of the cross 

section to determine the corrected measured discharge. The 

total discharge measured by an ADCP consists of discharge 

measured in a portion of the cross section and estimates of 

discharge in the unmeasured top, bottom, left, and right edges. 

Therefore, the final corrected measured discharge is computed 

using the ratio of the corrected and uncorrected measured 

portion of the discharge to correct the sum of the measured 

and top and bottom estimated discharges. Water velocities near 

the bank are assumed to be sufficiently low as to not cause a 

moving bed; therefore, no correction is applied to the left and 

right edge discharges. 

Mid-Section Method

The third GPS alternative is referred to as the midsection method and uses the ADCP to measure discharge 

in a manner similar to a standard cup-meter measurement. 

The hydrographer collects 20–25 velocity profiles with the 

ADCP at selected locations across the stream. A stationary 

water-velocity profile is collected by holding the ADCP in a 

specific location for a specified time and then averaging the 

data to obtain a mean velocity profile or a depth-integrated 

mean velocity at that location. The mid-section method is not 

biased by moving-bed conditions because the ADCP is held 

stationary for each measurement and bottom tracking is not 

referenced; therefore, the velocity measured by the ADCP 

is only the water velocity. The boat reference must be set to 

“none” in the software when making a mid-section measurement in moving-bed conditions, or the measured velocity will 

still be biased by the moving bed.

SonTek/YSI and Teledyne RD Instruments have 

developed software that supports mid-section discharge 

measurements. The velocity and depth data are collected 

from the ADCP, and the discharge is computed by using the 

mid-section method. The width for each measurement section 

is computed as half the distance from the current section to 

the previous section, plus half the distance from the current 

section to the next section. This width is then multiplied by the 

depth measured during the velocity measurement to compute 

an area for each section. Discharge for each of the sections is 

then computed by multiplying the mean water velocity by the 

cross-sectional area, and then the incremental discharges are 

summed to determine the total discharge.

The advantages to using the mid-section method are 

(1) a GPS is not required, (2) correct velocities are measured, 

(3) discharge-measurements procedures are familiar to 

hydrographers, and (4) software is available to automate 

the procedure. The disadvantages are (1) positions must be 

measured manually, (2) angled flow can introduce errors in the 

velocity measurement and must be handled carefully, 

(3) appropriate sampling times are required for each measurement, (4) the ADCP must be kept stationary because ADCP 

movement is not corrected, and (5) the entire cross section is 

not measured. 

Azimuth Method

The fourth GPS alternative is referred to as the azimuth 

method. The azimuth method is based on the fact that as an 

ADCP moves across the stream, a moving bed will cause the 

(B8)
Appendix B – Collecting Data in Moving-Bed Conditions 53

bottom-track-based ship track to be distorted in the upstream 

direction. If the azimuth between the starting and ending point 

of an ADCP transect is known, and the compass on the ADCP 

has been properly calibrated, the difference in azimuth of the 

course of the transect from that manually measured and that 

determined by the ADCP is a measure of the moving-bed 

velocity and can be used to compute a correction factor for 

the transect (fig. B-8). The advantages to using the azimuth 

method are that a GPS is not required and computations are 

simple. The disadvantages are (1) start and stop markers 

must be established, (2) the accuracy is dependent upon the 

measured azimuth and actual start and stop locations, (3) a 

compass calibration is required, (4) an accurate cross-sectional 

area projected perpendicular to the mean flow direction is 

required, (5) measured velocities are still biased low, 

(6) bottom tracking must be maintained, and (7) field applications have shown variable accuracy due to errors in azimuth 

measurements. This method is difficult to accurately conduct 

in the field and is not recommended.

Field Procedures

1. Establish starting and ending points and mark with 

buoys or other markers. Start and stop the measurement 

as closely as possible to these points (within 1 foot, 

if possible).

2. Use a hand-held compass to measure the azimuth from 

one buoy or marker to the other, and record this number.

3. Calibrate the compass on the ADCP using the internal 

calibration routines.

4. Collect data as you would for a typical discharge measurement, but take special care to start and stop the transects at the buoys or markers.

Processing Procedures

1. Process the data as you would for a typical 

discharge measurement.

2. For each transect, note the DMG, the course made 

good (CMG), and the total time for measuring along 

the transect.

3. Determine the difference between the measured azimuth 

and the CMG, and name this difference, C. This angle 

should be in the upstream direction (fig. B-8).

, C C C = − mg ref

where

C is the angle between the manually measured 

and ADCP-measured course,

Cmg is the azimuth of CMG measured by the 

ADCP, and 

Cref is the azimuth of CMG measured manually 

with a compass.

4. The moving-bed correction factor for each transect can be 

computed as:

sin( ) , MG

mb

D C

V

T

× =

where

Vmb is the moving-bed velocity,

DMG is the DMG, and 

T is the total measurement time for the transect.

5. Determine the cross-sectional area perpendicular to 

the mean flow direction (A) for the transect. The crosssectional area will be affected by the moving bed unless 

corrected to be perpendicular to the mean flow direction.

6. Compute the corrected discharge for the transect 

( ), Q Q V A corrected meassured mb = +

where

Vmb is the moving-bed velocity for the transect,

A is the cross-sectional area perpendicular to 

flow for the transect, and 

Qmeasured is the total unadjusted (biased) discharge for 

the transect.

7. Follow steps 2 through 6 for each transect used as part of 

the discharge measurement. The mean of the Qcorrected

for all transects is the corrected discharge for 

the measurement.

Figure B-8. The azimuth method.

(B9)

(B10)

(B11)

Flow

Azimuth of course made good effected by moving bed (Cmg)

Azimuth of true course made good (Cref)

C

DMG

Distance 

moved 

upstream

Flow

Azimuth of course made good effected by moving bed (Cmg)

Azimuth of true course made good (Cref)

C

DMG

Distance 

moved 

upstream
54 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Appendix C – Description of 

Water Modes

ADCPs typically have a default water mode that can be 

used in a wide range of water conditions. Special configuration 

and processing of the acoustic pulse(s) reduce random errors 

in velocity measurements and allow velocity measurements 

to be made in shallow water but typically impose a restriction 

on the conditions that can be measured. Brief descriptions of 

the default and special water modes currently (2008) available 

for the SonTek/YSI RiverSurveyor and the TRDI Rio Grande 

are presented to provide users with a better understanding of 

how to optimize the use of an ADCP for making discharge 

measurements in a variety of site conditions.

SonTek/YSI RiverSurveyor Water Modes

The SonTek/YSI RiverSurveyor ADCP operates primarily with a single water mode, but uses a shallow-water ping to 

add data from near the water surface in low-velocity shallowwater conditions. The RiverSurveyor is a narrowband ADCP. 

Narrowband ADCPs are pulse-to-pulse incoherent ADCPs. 

This means that the ADCP transmits one simple pulse into the 

water, per beam per measurement (ping), and the resolution 

of the Doppler shift takes place during the duration of the 

received pulse. Velocity measurements made using the narrowband technology are noisy (have a relatively large random 

error). The RiverSurveyor compensates for the large random 

error by pinging fast (up to 20 Hz) and averaging many pings 

together before reporting a velocity. Typical response from 

a RiverSurveyor is a velocity-profile measurement every 

5 seconds. Bottom-track pings are interleaved with the water 

pings once per second (SonTek/YSI, 2000).

The shallow-water ping is a pulse-coherent ping that is 

used in addition to the narrowband pings. The shallow-water 

ping measures the velocities in a depth cell that are above the 

standard velocity-profile depth cells. Because the shallowwater ping is a coherent ping, a potential exists for ambiguity 

errors. Ambiguity errors typically are avoided by the 

automatic parameters controlling the use of the ping, but the 

user can enable or disable the ping in the configuration part of 

the RiverSurveyor software. Enabling the shallow-water ping 

puts the ADCP in automatic mode where the shallow-water 

ping will only be used when there are three or fewer valid 

velocity-depth cells and the water velocity relative to the 

ADCP is less than 3.3 ft/s. The shallow-water ping is available 

on the 1.5-MHz and 3-MHz RiverSurveyors, which allow 

velocity data to be collected in water as shallow as 1.6 ft and 

1 ft, respectively (SonTek/YSI, 2007). 

TRDI Rio Grande and StreamPro Water Modes

The TRDI Rio Grande has five water modes, and the 

StreamPro has two water modes available to optimize the 

ADCP performance for the water velocity, turbulence level, 

and depth being measured. Because of the potential for large 

errors in the measured water velocity using Rio Grande water 

mode 8, the use of water mode 8 is discouraged, and no 

discussion of this mode is provided. The other four available 

Rio Grande water modes include (1) water mode 1—generalpurpose mode (2) water modes 5 and 11—low-velocity and 

low-turbulence modes, and (3) water mode 12—a fast pingrate mode. Although the configuration software for the Rio 

Grande configures the appropriate mode for the user, the user 

should understand the operation and limitations of the modes 

in order to collect quality data, even in difficult conditions. 

The two water modes available in the StreamPro include a 

general-purpose mode similar to the Rio Grande water modes 

1 and 12 and a low-velocity (less than 0.8 ft/s) mode.

Rio Grande Mode 1

Water mode 1 (WM1) is a general-purpose water mode 

for TRDI ADCPs (Teledyne RD Instruments, 2003). WM1 

typically is used in streams with a mean depth deeper than 

3.3 ft and(or) with velocities exceeding 3.3 ft/s. WM1 also 

can be used to measure slower velocities where water modes 

5 and 11 will not work (see discussion of Rio Grande Modes 

5/11). All other modes can be explained as a modification or 

enhancement of WM1. WM1 measures the Doppler shift using 

two phase-coded broadband pulses separated by a userspecified lag. The lag is inversely proportional to the radial 

ambiguity velocity, which is the maximum relative radial 

velocity (including boat speed and water speed) that can be 

accurately measured by the instrument. If the maximum boat 

velocity is assumed to equal the water velocity, an appropriate 

radial ambiguity velocity can be calculated to be approximately equal to the downstream water velocity (Teledyne 

RD Instruments, 2003). The recommended radial ambiguity 

velocity range is from 5.7 to 23 ft/s. The depth-cell size and 

lag between the pulses, and thus the ambiguity velocity, are 

key variables in determining the standard deviation of the 

random instrument noise present in velocity measurements. 

The recommended and commonly used depth-cell sizes for 

600 kHz and 1,200 kHz instruments are 1.6 ft and 0.8 ft, 

respectively. This results in standard deviations of instrument 

noise of between 0.4 and 0.7 ft/s, depending on the radial 

ambiguity velocity value. The standard deviations will 

increase greatly for smaller depth-cell sizes. 

Rio Grande Modes 5/11

Water modes 5 and 11 (WM5 and 11) are pulse-to-pulse 

coherent modes that use short phase-encoded broadband 

pulses. Similar to WM1, two pulses are transmitted; however, 

unlike WM1, the lag between the pulses for WM5 and 11 is 

long and variable. The lag is equal to the time for the first 

pulse to travel to the bottom and back. After the signal from 

the first pulse is received at the transducer face, the ADCP 

transmits the second pulse. The ADCP determines how long 

to wait before sending the second transmission from the 

water-depth-measurement part of the bottom-track measurement. This creates a very long lag with extremely low velocity 

single-ping standard deviations, typically less than 0.06 ft/s 
Appendix C – Description of Water Modes 55

with depth-cell sizes of 0.16 ft and 0.33 ft for 1,200-kHz and 

600-kHz instruments, respectively. 

A long lag can cause a problem with residence time. 

Residence time is the time that a group of scatterers remains 

in a region for both pulses to ensonify the scatterers. If the 

velocity is very slow, most scatterers will remain in the same 

region for the time it takes both pulses to pass. Some decorrelation will occur because new scatterers enter the region as 

others leave. Nevertheless, if the number of scatterers entering 

and leaving is small, the correlation will be high and the data 

will be valid. If the velocity is too fast, and the scatterers move 

more than one-fourth to one-half of the transducer diameter 

with new scatterers introduced, the correlation between the 

two pulses will be low, and the data will be invalid. 

The low-velocity standard deviations for WM5 and 11 

make them excellent choices for discharge measurements 

where stream conditions permit use of these modes. The characteristics of these water modes that produce a low-velocity 

standard deviation also create significant limitations in the 

application of these water modes. Because of the long lag, the 

ambiguity velocity is very low and could render the modes 

nearly useless; however, an ambiguity-resolving depth cell is 

used to help resolve the ambiguity and allow a lower ambiguity velocity than the actual velocity of the water (Teledyne 

RD Instruments, 2003). The time-dilation technique used 

to determine the velocity in the ambiguity-resolving depth 

cell and the bin-to-bin tracking algorithm used to apply the 

ambiguity velocity to consecutive depth cells limits the use of 

WM5 and 11 to conditions with low turbulence and low shear. 

In WM5, the ambiguity-resolving depth cell extends from the 

end of the blank to the lesser of 2 ft or 85 percent of the shallowest beam, and the ambiguity-resolving depth cell must be 

at least 1 ft long. In WM11, the ambiguity-resolving depth cell 

is centered between the end of the blank and 85 percent of the 

shallowest beam and has a maximum length of 7.5 ft. Unlike 

WM5, which requires an ambiguity-resolving depth cell of 

at least 1 ft, WM11 continues to operate but stops computing 

ambiguity when the ambiguity-resolving depth cell becomes 

smaller than 1 ft. Shear caused by coarse bed material will 

often cause these modes to fail. Due to the short pulses and 

long lag, WM5 and 11 are limited to shallow depths (less than 

13 ft for 1,200 kHz and less than 26 ft for 600 kHz) and slow 

velocities (typically less than 3.3 ft/s). 

Rio Grande Mode 12

WM12 was designed to allow data collection in streams 

shallower than could be measured with WM1 and with 

velocities greater than could be measured with WM5 and 11. 

WM12 is essentially a fast ping rate WM1. The concept for 

WM12 is based on the fact that random noise is reduced by the 

square root of the number of samples. The velocity standard 

deviation increases as the WM1 depth-cell size is reduced. 

One method of reducing the velocity standard deviation is to 

collect and average more measurements. Averaging multiple 

WM1 pings (two pulses for each ping) only realizes gains 

in the transmission time of the data to the computer. WM12 

is designed so that the heading and pitch-and-roll sensors 

are only read at the beginning of the averaging period, the 

individual pings are averaged in phase space, and only the 

average is transformed into water velocities. This design 

eliminates some of the processing overhead and potential for 

averaging ambiguity velocity errors associated with WM1. 

The ping rate for WM1 is approximately 2–3 Hz, and the ping 

rate for WM12 is 10–20 Hz (depending on number of depth 

cells). However, since the heading and pitch-and-roll sensors 

are sampled only at the beginning of the averaging period, 

changes in heading, speed, pitch, or roll will lead to errors in 

the measured velocity. Thus, the sampling period needs to be 

short; generally 1 second or less is recommended. Although 

WM12 was designed for use with small depth cells in shallow 

water, WM12 can be used anywhere WM1 can be used, 

provided the ambiguity velocity is set properly as in WM1. 

The velocity standard deviation for WM12 cannot be stated as 

broadly as for the other water modes because WM12 is more 

configurable and the velocity standard deviation is dependent 

on the sampling period, the depth-cell size, the number of 

pings fit into the sampling period, and the ambiguity velocity.

StreamPro Mode 12

The StreamPro does not use water mode 12 as 

implemented in the Rio Grande, rather water mode 12 in 

the StreamPro (referred to hereafter as WM12sp) is more 

similar to a modified multi-ping Rio Grande water mode 1, 

which pings fast. For every water ping (WP) in WM12sp, 

the instrument sends and processes eight full WM1 pings. 

Each ping is fully processed, stored, and averaged with the 

other seven pings. Users cannot control the eight pings. The 

user can control the WP setting, which by default is set to 6 

to obtain an ensemble output rate of 1 second. With default 

settings, 48 WM1 pings are averaged together and reported 

as the ensemble output. Ambiguity errors could occur in 

the individual pings and would be hidden by the averaging 

process; however, the StreamPro has a fixed ambiguity velocity of 11 ft/s, making an ambiguity error nearly impossible for 

the StreamPro applications. For WM12sp in the long-range 

mode, the number of pings processed is reduced to maintain 

an ensemble output rate of 1 second. The custom commands 

for WM12sp are limited to the blanking distance (0–1.6 ft), 

number of depth cells (0–20 depth cells) and depth-cell size 

(0.06–0.66 ft).

StreamPro Mode 13, Water Mode C, 

Low Noise Mode

The StreamPro has a second water mode that has a lower 

random noise than does WM12sp and that can be used to 

measure water velocities less than about 0.8 ft/s in water less 

than 3.3 ft deep. WM13 is a long-lag pulse coherent mode, 

which transmits multiple pulses at different lags. WM13 has 

no ambiguity-resolving depth cell as in Rio Grande WM5 

and 11; the ambiguity in each depth cell is resolved using a 

proprietary approach. 
56 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Appendix D – Beam-Alignment Test

Introduction

One source of error in ADCP measurements is misalignment of beams in the instrument. This error can be checked 

and corrected by the user. The equations for both three-beam 

and four-beam (Appendix A) ADCPs assume that the beams 

are in perfect alignment and result in nominal transformation 

matrices for three-beam and four-beam systems. The nominal 

transformation matrix for a 25-degree three-beam system, such 

as the SonTek/YSI RiverSurveyor, is

 

 

 

0 - 1.366 1.366

1.577 - 0.789 - 0.789

0.368 0.368 0.368

         

The nominal transformation matrix for a 20-degree four-beam 

system, such as the TRDI Rio Grande, is

























1.0337 1.0337-1.0337-1.0337

0.2661 0.2661 0.2661 0.2661 

1.4619- 00 1.4619

1.4619- 1.4619 00

If the beams were misaligned during manufacturing, a 

custom transformation matrix to correct the misalignment is required. If the wrong transformation matrix 

is used, the water and bottom-track velocities will be 

consistently biased. The validity of the transformation 

matrix stored in the instrument can be determined 

by computing the ratio of the bottom-track and GPS 

straight-line distances over a long course, provided 

the instrument has a compass; for the StreamPro, 

no instrument rotation occurs during the test. Note: 

Procedures presented herein have not been validated 

in the field for StreamPro ADCPs.

Description of Procedure

The beam-alignment test is conducted by 

traversing a long (1,200–2,500 ft) course at a constant 

compass heading and speed while simultaneously 

recording GPS (GGA or VTG) and ADCP data. The 

length of the course depends on the accuracy of the 

GPS being used. The length of the course should 

be such that the error in GPS position is less than 

0.1 percent of the length of the course. The ratio of 

the straight-line distance traveled (commonly called 

the DMG) as measured by bottom tracking with 

the ADCP and the straight-line distance traveled as 

measured by the GPS is computed. This ratio is referred to as 

the bottom-track-to-GPS ratio. A reciprocal traverse, which 

is a course of the same length at a heading approximately 

180 degrees from the previous pass, is made and the ratios of 

the two passes are averaged. This procedure is repeated for 

a total of four times (eight passes altogether) while rotating 

the ADCP 45 degrees between each pair of courses. When 

the bottom-track-to-GPS ratio is less than 0.995, ADCP 

measurements most likely have a negative bias error, and when 

the bottom-track-to-GPS ratio is greater than 1.003, the ADCP 

most likely has a positive bias error (Oberg, 2002). A value 

for the bottom-track-to-GPS ratio of 0.995 corresponds to a 

–0.5-percent error in bottom-track velocity measurements. A 

value for the bottom-track-to-GPS ratio of 1.003 corresponds 

to a +0.3-percent error in bottom-track velocity measurements. 

The skewed criteria are due to a known potential for ADCPs 

to have a slight negative bias due to terrain effects. A wellcalibrated ADCP should have bottom-track-to-GPS ratios 

of approximately 0.998 or 0.999. A form for documenting 

the beam-alignment tests is shown in figure D-1 (Oberg and 

others, 2005).

Figure D-1. Acoustic Doppler current profiler (ADCP) beam-alignment test form.

.

.
Appendix D – Beam-Alignment Test 57

Step-by-Step Procedure

The following procedures should be followed when 

conducting the distance tests.

1. Conduct internal ADCP diagnostic tests (if available).

2. Lower the ADCP into the water, noting which beam is 

facing forward.

3. Using the data-collection software, begin pinging, but do 

not begin recording data. 

4. Open a window in the software that will display the 

bottom-track-to-GPS DMG ratio. 

5. Bring the boat to a constant speed and heading and note 

the heading. The speed should be fast enough to traverse 

the course in a reasonable time but not so fast as to cause 

invalid bottom-track data. 

6. Once the boat is at the desired speed and heading, begin 

recording data. After traveling a minimum of 4,250 ft, 

record the bottom-track-to-GPS DMG ratio, stop 

recording, and then slow the boat and turn to a heading 

180 degrees from the previous heading. 

7. Bring the boat to a constant speed. Record data for 

this reciprocal pass. At the end of the pass, record the 

bottom-track-to-GPS ratio again. It is important to NOT 

slow the boat or change heading until recording 

is stopped.

8. Repeat this procedure while rotating the ADCP 

45 degrees between each pair of courses until the ADCP 

has been rotated four times.

9. Average the bottom-track-to-GPS DMG ratio for each 

reciprocal pair.

10. Review the averaged bottom-track-to-GPS DMG ratio 

for all rotations and verify that all values are between 

0.995 and 1.003. If values are outside of this range, have 

the instrument serviced by the manufacturer.
58 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Appendix E – Forms and Quick-Reference Guides

Figure E-1. Pre-Field checklist of equipment for discharge measurements with acoustic Doppler 

current profilers (ADCPs).
Appendix E – Forms and Quick-Reference Guides 59

Figure E-2. Sample acoustic Doppler current profiler (ADCP) discharge-measurement field form.
60 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Figure E-3. Front page of quick reference guide for making acoustic Doppler current profiler (ADCP) 

discharge measurements with Teledyne RD Instruments Rio Grande profilers (modified from Oberg and 

others, 2005).

Teledyne RD Instrument Rio Grande Quick Sheet

 DISCHARGE MEASUREMENT PROCEDURE

1. Setup ADCP and Other Equipment 

a. Attach ADCP to mount or tethered boat

b. Attach safety line to ADCP

c. Turn on computer before connecting ADCP or data radios

d. Turn off all automated field computer tasks/power saver settings 

e. Connect ADCP\GPS\field computer\data radios

f. Verify communication with all devices

g. Check and set ADCP clock time to appropriate time

h. Measure water temperature, record, and compare to ADCP measured temperature

2. Configure ADCP

a. Locate appropriate measurement section / collect trial transect, if needed

b. Select measurement site with uniform flow, no rapid drop-offs

c. Minimize unmeasured area

d. Determine maximum profiling depth

e. Configure ADCP using automated software tools, if possible

f. Measure salinity and if not zero, enter salinity in ADCP software

g. Measure ADCP depth and record in software and notes (beware of pitch and roll)

h. Fill out all field sheet with configuration and other information

3. Prepare for discharge measurement

a. Perform ADCP diagnostic tests and log results

b. Perform and document compass calibration procedure (total error < 1 deg preferred)

c. Record moving-bed test (stationary or loop)

Duration of test = 600 seconds

Stationary moving bed test

Vmb= Dist Upstream / Duration

Moving bed if:

Anchored or tethered Vmb/Vw> 0.01

Not Anchored Boat Vmb/Vw> 0.02

GPS Referenced Vmb/Vw> 0.01

Vw is the mean water velocity

Compass must be calibrated

Loop test

Duration at least 3 minutes

Boat speed less than 1.5 * water speed

Vmb= Dist Upstream / Duration

Moving bed if:

Vmb > 0.04 ft/s and Vmb/Vw> 0.01

Vw is the mean water velocity

b. Use GPS or other appropriate technique, if a moving bed is present

c. Establish start/stop points

i. Need minimum of two depth cells with “good” velocity on each edge

ii. May use buoys, pilings, poles, or other reference (avoid ferrous objects)

3. Make discharge measurement

a. Position boat at starting edge-of-water (two ‘good’ depth cells)

i. Begin recording data

ii. Measure and record distance to shore

a. Hold position for minimum of 10 ensembles

b. Drive boat across the river

i. Boat speed should be less than or equal to the water speed

ii. Be a smooth operator

d. Approach ending shore slowly

i. Hold position for minimum of 10 ensembles

ii. Stop recording

iii. Measure and record distance to shore

iv. Collect 4 or more transects

v. All transects must be within 5 percent of the mean discharge; except for 

unsteady flow conditions; if not, another set of transects should be measured and

all transects collected averaged for the final discharge.

e. Evaluate data in field, looking for potential problems in the data

f. Make temporary backups before leaving the site
Appendix E – Forms and Quick-Reference Guides 61

Figure E-4. Back page of quick reference guide for making acoustic Doppler current profiler (ADCP) discharge 

measurements with Teledyne RD Instruments Rio Grande profilers.

Baud Rates

ADCP Baud Rate: A baud rate lower than 

38.4k baud will result in less data being 

collected. Set ADCP baud rate in BB-Talk 

using CB to set baud rate. 9600 – CB411, 

19.2k – CB511, 38.4k – CB611, 57.6k –

CB711, 115.2 – CB811. Set BB-Talk to “Send 

CK on Baud Rate change (CB command)”.

GPS Baud Rate: The minimum acceptable 

GPS baud rate depends on the number of 

NMEA 0183 data types being output but the 

following are good general guidelines.

GPS Update Rate Baud Rate

1 Hz 4800 or higher

5 Hz 19.2k or higher

10 Hz 38.4k or higher

Missing Data

Lost Ensembles: Lost ensembles are a result

of a communications problem. 

Solution:

1. Disable antivirus, power management, 

etc.

2. Try lowering the baud rate.

3. Change serial ports or serial port 

adapters.

Bad Ensembles: Bad ensembles are a result 

of site conditions or water mode selection. 

Solution: 

1. Try a different cross section. 

2. If using water modes 5 or 11, try water 

mode 12. 

3. Use the bottom track tabular view to 

determine if bad ensembles are 

caused by bottom track. If so, try 

bottom mode 7 or a different cross 

section.

Draft Measurement

(figure adapted from 

Environment Canada, 2004)

Recommendations and Limitations

Rio Grand Model > 1200/1200ZH 600

Blanking Distance (WF) 

All Modes 0.82 ft (25 cm) 0.82 ft (25 cm)

Minimum Depth Cell (Bin) Size

Mode 1 0.82 ft (25 cm) 1.64 ft (50 cm)

Mode 5 or 11 0.16 ft (5 cm) 0.33 ft (10 cm)

Mode 12 0.16 ft (5 cm) 0.33 ft (10 cm)

Maximum Profiling Range

Mode 1 or 12 65 ft 230 ft

Mode 5 or 11 13 ft 26 ft

Mode 5 or 11 with WZ3 22 ft 42 ft

Maximum Relative Velocity

Mode 1 or 12 32 ft/s 32 ft/s

Mode 5 or 11 ~2.3 ft/s ~3.3 ft/s

Mode 5 or 11 with WZ3 < 2.3 ft/s < 2.3 ft/s

Approximate Velocity Standard Deviation

Mode 1, WV175 Bin Size: 0.82 ft

SD: 0.43 ft/s

Bin Size: 1.64 ft

SD: 0.43 ft/s

Mode 5/11 Bin Size: 0.16 ft

SD: < 0.03 ft/s

Bin Size: 0.33 ft

SD: < 0.03 ft/s

Mode 12, WV175, 10 

subpings

Bin Size: 0.82 ft

SD: 0.13 ft/s

Bin Size: 1.64 ft

SD: 0.13 ft/s

Bin Size: 0.33 ft

SD: 0.33 ft/s

Bin Size: 0.82 ft

SD: 0.30 ft/s

Bin Size: 0.16 ft

SD: 0.16 ft/s

Bin Size: 0.33 ft

SD: 0.49 ft/s

• Modes 1, 5, and 11 should be configured for minimum bin 

size.

• Mode 12 should be configured for a bin size smaller than 

the mode 1 bin size only as needed to measure in shallow 

areas. Mode 12 standard deviation will increase with a 

decreasing bin size.

• Mode 12 should be configured to report data at least once 

per second and more often in turbulent conditions. This can 

be adjusted by setting the number of subpings in the WO 

command (WOss,tt, change the ss to a lower value). The 

standard deviation will increase as the number of subpings 

is lowered.

• Modes 5 and 11 will not work in turbulent water or in sites 

with rough bottoms. If water is deep, the WZ03 can be used 

to extend the range, but then the turbulence and velocity 

must be very low. The precise velocity and turbulence 

limitations of modes 5 and 11 cannot be specified.

Helpful Shortcuts

F4 Start/Stop Pinging

F5 Start/Stop Transect

F8 Toggle Bank

F9 Toggle Ensemble Header Tabular view

F11 Toggle Detailed Discharge/Composite 

Tabular view

F12 Toggle Discharge Summary Tabular 

view

Ctrl-B Reference - Bottom Track

Ctrl-G Reference - GPS (GGA)

Ctrl-V Reference – GPS (VTG)

Ctrl-N Reference - None

(when Measurement Control window selected)

Ctrl-K Add Note 

(when Ship Track plot selected)

Ctrl-PgDn Scale Sticks Down 

Ctrl-PgUp Scale Sticks Up

Cable Diagram

ADCP Description

Computer 

/ Battery

1 RS-232 Receive => RS232-Transmit 3

2 RS-232 Transmit => RS232-Receive 2

3 Signal Ground 5

4 Power positive (red) +

8 Power negative (black) -
62 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Figure E-5. Front page of quick reference guide for making acoustic Doppler profiler (ADP) discharge 

measurements with Sontek/YSI RiverSurveyor profilers (modified from Oberg and others, 2005).

SonTek RiverSurveyor Quick Sheet

 DISCHARGE MEASUREMENT PROCEDURE

1. Setup ADCP and Other Equipment 

a. Attach ADCP to mount or tethered boat

b. Attach safety line to ADCP

c. Turn on computer before connecting ADCP or data radios

d. Turn off all automated field computer tasks/power saver settings 

e. Connect ADCP\GPS\field computer\data radios

f. Verify communication with all devices

g. Check and set ADCP clock time to appropriate time

h. Measure water temperature, record, and compare to ADCP measured temperature

2. Configure ADCP

a. Locate appropriate measurement section / collect trial transect, if needed

b. Select measurement site with uniform flow, no rapid drop-offs

c. Minimize unmeasured area

d. Determine maximum profiling depth

e. Configure ADCP using automated software tools, if possible

f. Measure salinity and if not zero, enter salinity in ADCP software

g. Measure ADCP depth and record in software and notes (beware of pitch and roll)

h. Fill out all field sheet with configuration and other information

3. Prepare for discharge measurement

a. Perform ADCP diagnostic tests and log results

b. Perform and document compass calibration procedure (total error < 1 deg preferred)

c. Record moving-bed test (stationary or loop)

Duration of test = 600 seconds

Stationary moving bed test

Vmb= Dist Upstream / Duration

Moving bed if:

Anchored or tethered Vmb/Vw> 0.01

Not Anchored Boat Vmb/Vw> 0.02

GPS Referenced Vmb/Vw> 0.01

Vw is the mean water velocity

Compass must be calibrated

Loop test

Duration at least 3 minutes

Boat speed less than 1.5 * water speed

Vmb= Dist Upstream / Duration

Moving bed if:

Vmb > 0.04 ft/s and Vmb/Vw> 0.01

Vw is the mean water velocity

d. Use GPS or other appropriate technique, if a moving bed is present

e. Establish start/stop points

iii. Need minimum of two depth cells with “good” velocity on each edge

iv. May use buoys, pilings, poles, or other reference (avoid ferrous objects)

4. Make discharge measurement

a. Position boat at starting edge-of-water (two ‘good’ depth cells)

i. Begin recording data

ii. Measure and record distance to shore

b. Hold position for minimum of 10 ensembles

c. Drive boat across the river

i. Boat speed should be less than or equal to the water speed

ii. Be a smooth operator

d. Approach ending shore slowly

i. Hold position for minimum of 10 ensembles

ii. Stop recording

iii. Measure and record distance to shore

iv. Collect 4 or more transects

v. All transects must be within 5 percent of the mean discharge; except for unsteady 

flow conditions; if not, another set of transects should be measured and all 

transects collected averaged for the final discharge.

e. Evaluate data in field, looking for potential problems in the data

f. Make temporary backups before leaving the site
Appendix E – Forms and Quick-Reference Guides 63

Figure E-6. Back page of quick reference guide for making acoustic Doppler profiler (ADP) 

discharge measurements with Sontek/YSI RiverSurveyor profilers.

Baud Rates

GPS Baud Rate: The minimum 

acceptable GPS baud rate depends 

on the number of NMEA 0183 data 

types being output but the following 

are good general guidelines.

GPS 

Update Rate Baud Rate

1 Hz 4800 or higher

5 Hz 19.2k or higher

10 Hz 38.4k or higher

Draft Measurement

(adapted from Oberg and others, 2005)

0.75 feet

0.23 meters

1,500 kHz

0.71 feet

0.22 meters

3,000 kHz

Helpful Shortcuts

F5 Start Pinging

F6 Stop Transect

F7 Start Recording

Alt-F7 Stop Recording

Ctrl-B Reference - Bottom Track

Ctrl-G Reference - GPS 

Ctrl-E English Units

Ctrl-M Metric/SI Units

Ctrl-S Communications Dialog

Ctrl-U User Setup

Ctrl-H Hardware Dialog

Ctrl-Y Q Summary

Ctrl-D Q Calculation Dialog

Ctrl-T Q Report

+ (keypad) Scale Sticks Up

- (keypad) Scale Sticks Down

Recommendations and Limitations

ADP

Frequency

(kHz)

Profiling Range

[min. – max.]

(ft)

Cell Size

[min. – max.]

(ft)

Blanking Distance

[minimum]

(ft)

Max. Bottom

Tracking Depth

(ft)

500 10 - 394 3.3 – 39.4 3.3 443

1,000 3.9 - 131 0.82 – 16.4 2.3 131

1,500 3.0 - 82 0.82 – 13.1 1.3 98

3,000 2.0 - 20 0.49 – 6.6 0.66 33

ADP

Frequency

(kHz)

Ping

Rate

(Hz)

Cell

Size

(ft)

Single Ping

Std. Dev.

(ft/s)

1-Second

Std. Dev.

(ft/s)

5-Second

Std. Dev.

(ft/s)

500 4.5 1.64 3.08 1.44 0.66

500 4.5 3.28 1.54 0.72 0.33

1,000 12 0.82 3.08 0.88 0.39

1,000 12 1.64 1.54 0.46 0.20

1,500 9 0.82 2.07 0.69 0.30

1,500 9 1.64 1.02 0.33 0.16

3,000 20 0.49 1.71 0.39 0.16

3,000 20 0.82 1.02 0.23 0.10

Stand-Alone ADP Connector Wiring

(adapted from Sontek, 2001)

IL-8-MP

Pin No.

MIL-16-MP 

Pin No. RS232 RS422

1 1 Vpower Vpower

2 10 Data out Tx+

3 11 Data in Tx4 4 & 9 Drain Drain

5 5 Not used Not used

6 6 Not used Rx+

7 14 Not Used Rx8 16 Ground Ground
64 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Appendix F – Measurement Review Procedures

Teledyne RD Instruments Rio Grande and StreamPro ADCPs

1. Load Data

•	 Load measurement file (File→Open Measurement or Ctrl-O). 

•	 Select Transect and Reprocess Transect (Shift+F5).

2. Check Stick Ship Plots

•	 Look at stick ship plot.

•	 Verify velocity reference (BT or GGA). 

•	 Step through depths using the down-arrow key (↓) 

(if problems are observed, look at velocity contour 

plots or intensity / back scatter plots).

3. Velocity-Magnitude Contour

•	 Review velocity-magnitude contour. 

•	 Scale as appropriate. 

•	 Look for missing (referred to as “lost” 

in WinRiver) or invalid (referred to as 

“bad” in WinRiver) data, bed contour, 

lost ensembles, or other errors.

4. Composite Tabular—Review

•	 Number of ensembles (total) vs 

•	 (1) Bad ensembles (invalid)

•	 (2) Lost ensembles (missing).

•	 What is value for “% Bad Bins (depth cells)?

•	 Is water temperature realistic? 

•	 Do the edge discharges appear reasonable?

•	 Do edge discharges have correct signs?
Appendix F – Measurement Review Procedures 65

5. System Parameters

•	 Press F9 to check system parameters.

•	 Does the information there (Frequency, Firmware, 

Water and Bottom modes, Bin Size) match the direct 

commands (F3) specified in the configuration file?

•	 Does the information match the field form?

6. Projected Velocity Contour

•	 Press F2 to set angle for projected velocity 

contour plot and verify that value for the 

angle is correct. “Freeze” that value for the 

first transect—assuming that flow is 

uni-directional.

•	 Scale as appropriate.

•	 Look for reverse / bi-directional flow.

7. Error Velocity

•	 Look for ambiguity errors, 3-beam solutions. 

Outliers can be related to ambiguity errors or 

turbulence.

8. Configuration – Direct Commands

•	 Press F3 and check direct commands (Wizard and 

User).

•	 Was the Config Wizard used?

•	 Are the Wizard and User commands set correctly for 

ADCP and flow conditions?

9. Configuration – DS/GPS

•	 Check to see if Depth Sounder is used. 
66 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

10. Configuration – Discharge

•	 Are extrapolation methods correct? 

•	 Review edge types selected.

•	 Were water profile depth cells cutoff? Why? Is it 

documented?

•	 Correct number of shore pings (10)?

11. Configuration – Edge Estimates

•	 Are Edge Estimates consistent with field form? If 

not, has explanation been supplied? 

•	 Are Shore Distances estimated rather than measured?

•	 Are the estimated edge discharges reasonable for this 

section?

12. Configuration – Offsets

•	 Does the Transducer Depth match the depth 

recorded on the field form? 

•	 Has MagVar been entered for discharge measurements made using GPS as a reference?

13. Configuration – Processing

•	 Check area computation method.

•	 Are thresholds used? If so, are they used correctly?

•	 Is Salinity set correctly? Compare field form.

•	 Are 3-beam solutions for the water- velocity (WT) 

data being used? (This is generally discouraged.) 
Appendix F – Measurement Review Procedures 67

14. Configuration – Recording

•	 GPS recorded?

•	 Review comments field.

15. Time Series

•	 Review time-series plots. 

o Compare Water speed and Boat 

Speed time series.

o Review Pitch-and-roll plot for 

excessive pitch-and-roll.

•	 Look for consistency, spikes, 

drop-outs, and large fluctuations.

16. Evaluate Extrapolation Method

•	 Open View→Graphs→Profile Discharge plot.

•	 Average 10–20 ensembles (Ctrl-F9). 

•	 Modify extrapolation method as necessary.

17. Repeat

•	 Review all transects used during measurement.

18. Check Whole Measurement

•	 Open Discharge Summary (F12).

•	 Are all discharges within 5 percent? In other words, are any rows red?

•	 Were reciprocal transect pairs obtained?

•	 Check the following for consistency.

 i. Total area

ii. Widths

iii. Boat speed

 iv. Flow direction

 v. Duration

vi. Compare boat speed with water speed

Example Discharge History Tabular for a “good” discharge measurement 
68 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

Example Discharge History Tabular for discharge measurement with “outliers”
Appendix F – Measurement Review Procedures 69

Sontek/YSI RiverSurveyor ADP 

1. Load Data

•	 Load measurement file (File→Open Measurement or 

Ctrl-O). 

•	 Select transect and Reprocess Transect (Shift+F5).

2. Check Ship Plots

•	 Look at ship plot.

•	 Verify velocity reference (BT or GPS). 

•	 Step through depths (if problems are observed, 

look at velocity contour plots or intensity / SNR 

plots).

3. Velocity-Magnitude Contour

•	 Review velocity-magnitude contour. 

•	 Scale as appropriate. 

•	 Look for invalid or missing data, bed contour, 

or other errors.
70 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

4. Tabular Data

•	 Number of profiles

•	 Is water temperature realistic? 

•	 Do the edge discharges appear reasonable?

•	 Do edge discharges have correct signs?

5. Velocity-Direction Contour

•	 Go to View→Contour Control Box. Select Velocity

and Direction data.

•	 Scale as appropriate.

•	 Look for reverse / bi-directional flow.

6. Configuration

•	 Press Ctrl-U and check configuration.

•	 Check depth-cell size, range, and blank.

•	 Does the Transducer Depth match the depth 

recorded on the field form? 

•	 Has MagVar been entered for discharge measurements made using GPS as a reference?
Appendix F – Measurement Review Procedures 71

7. Velocity Profile Extrapolation

•	 Select Processing→Velocity Profile Extrapolation.

•	 Right-click on profile graph and select profile 

extrapolation.

•	 Are extrapolation methods correct? 

•	 Review edge types selected.

•	 Were water profile depth cells cut off? Why? 

Is it documented?

8. Time Series

•	 Review time-series plots. 

•	 Right-click on the y-axis of the bar chart and select 

the appropriate variable.

•	 Compare Water Speed and Boat Speed time series.

•	 Review pitch-and-roll plot for excessive pitch-androll.

•	 Look for consistency, spikes, drop-outs, and large 

fluctuations.

9. Discharge Computation

•	 Select Processing→Discharge Calculation.

•	 Are Edge Distances consistent with those recorded 

on the field form? If not, has explanation been supplied? 

•	 Are Edge Distances estimated rather than measured?

•	 Are the estimated edge discharges reasonable for this 

section?

•	 Recompute discharge.

•	 Check for consistency and reasonableness.

10. Repeat

•	 Review all transects used for measurement.
72 Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat 

11. Check Whole Measurement

•	 Select File→Discharge Summary or Ctrl-Y

•	 Are all discharges within 5 percent? 

•	 Were reciprocal transect pairs obtained?

•	 Check the following for consistency.

o Total area

o Widths

o Boat speed

o Flow direction

o Duration

o Compare boat speed to water speed
Prepared by:

USGS Publishing Network

Raleigh Publishing Service Center

3916 Sunset Ridge Road

Raleigh, NC 27607

For additional information regarding this publication, contact:

David S. Mueller

Office of Surface Water

9818 Bluegrass Parkway

Louisville, Kentucky 40299

phone: 1-502-493-1935

email: dmueller@usgs.gov
Mueller and Wagner—Measuring Discharge with Acoustic Doppler Current Profilers from a Moving Boat—Techniques and Methods 3–A22

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