Interim Policy and Technical Guidance on Broadband Acoustic Doppler Current Profilers

In Reply Refer To:                                      January 31, 1996
Mail Stop 415


Subject:  Interim Policy and Technical Guidance on Broadband Acoustic 
          Doppler Current Profilers

This memorandum supersedes Office of Surface Water Technical Memorandum 
93.15, Interim Policy and Technical Guidance on Broadband Acoustic 
Doppler Current Profilers (ADCPs).  The purpose of this memorandum is 
to provide information on the ADCP work group and to update policy and 
technical guidance for the operation of broadband ADCP's.

The Office of  Surface Water (OSW) has sponsored an ADCP work group to 
provide operational guidance to users.  The work group, which includes 
members from Environment Canada and the Corps of Engineers, has put on 
three ADCP workshops--two in the United States and one in Canada.  They 
have planned and commissioned the preparation of three reports: a 
quality-assurance plan, an operational manual, and a report on a 
verification study.  The work group also has established an Internet 
news group called usgs.adcp for dissemination and discussion of ADCP 

The quality-assurance plan has been published as Open-File Report 95-
701, Quality Assurance Plan for Discharge Measurements Using Broadband 
Acoustic Doppler Current Profilers, by Stephen W. Lipscomb.  Copies are 
available from OSW.  The operational manual is in colleague review.  
The verification study, comparing ADCP-produced discharges with stable-
rating discharges at 12 gaging stations, has been completed. The report 
is approved and is being prepared for printing.

System performance and operation characteristics of ADCP's are changing 
as hardware and software continue to improve.  Frequent revisions of 
software, firmware, and documentation revisions are expected.  Policy 
and technical guidance will thus be subject to change and some 
information may be specific to a particular system (i.e. signal 
frequency), or version, which may not be the most current.


The following policies apply to use of the ADCP for making velocity-
profile and discharge measurements from moving boats. 


The ADCP can accurately measure discharge for only a limited range of 
flow conditions.  Based on manufacturer recommendations and preliminary 
measurement-verification information, the following conditions must be 
met for general use of the ADCP to measure velocity profiles or 
discharge.  Measurements made at or beyond these limits generally will 
not produce accurate results and will require specific error analysis.
| Average               | Average                 | Maximum Unmeasurable Flow Due |
|                       |                         |                               |
| Depth                 | Velocity                | To Limited Depth or Velocity  |
|                       |                         |                               |
| between 4.5 and 66 ft | between 0.4 and 12 fps  | 10 percent                    |

These and other measurement conditions (site characteristics and 
instrument operation) must be assessed to correctly set up the 
instrument and software, to determine appropriate measurement 
techniques, and to check the results for errors.  The ADCP Discharge 
Measurement Notes form or similar document should be used to record 
measurement conditions.   When a measurement condition appears 
problematic, measurement documentation should include: (1) a brief 
description of the condition; (2) methods used to determine if the 
condition (i.e. mobile stream bed) is significant to the measurement; 
and (3) how the effects of the conditions were accounted for (i.e. 
appropriate instrument operating modes, configuration file settings, 
tests, and error analyses).  Measurement conditions to be assessed 
include the following:

 Mobile stream bed

 Channel edge

 Pitch and roll of boat platform

 Measurement starting and stopping procedures

 Side-lobe interference

 Heading (compass) errors

 Shallow-depth-caused errors not covered elsewhere

 Vessel speed during measurement

 Vessel course during measurement

A wide range of flow conditions may be encountered when using an ADCP.  
Considerable judgement must be exercised by the ADCP operator.  The 
following general guidelines are provided:

1.  Under steady flow conditions a minimum of four transects will be 
    made (two in each direction).  The reported discharge will be the 
    average of the transected discharges.  If any of the four transect 
    discharges differ more than 5 percent of the mean discharge, then at 
    least one more set (four transects) will be obtained.

2.  Under rapidly varying flow conditions, it may be necessary to make a 
    single transect as a discharge measurement.  The rationale for using 
    less than four transects should be documented and permanently stored 
    with the discharge measurement and documented in applicable station 

3.  Use of an ADCP does not reduce the importance of site selection for 
    discharge measurements.  The guidelines provided in Water Supply 
    Paper 2175 are still applicable.

4.  When bed movement is suspected, the vessel should be anchored for 
    about 10 minutes in a section where the possibility of bed movement 
    exists, provided that this can be done safely.  During this time ADCP 
    bed-tracking data should be collected and examined to reveal any 
    apparent upstream movement of the boat relative to the channel 
    bottom.  If apparent upstream boat movement exists, then the ADCP 
    measured water velocity may be affected by bed movement, and the 
    ADCP indicated discharge may be lower than the true discharge.

5.  As a general rule of thumb, boat speed across the transect should be 
    less than or equal to the average water velocity.  In general, a 
    transect should not take less than about 3 minutes or 
    45 ensembles to complete.


Successful application of the ADCP requires considerable experience and 
informed judgement based on an understanding of the physical and 
computational factors which affect the accuracy of measurements or 
individual components of measurements.  These factors must be understood 
and evaluated in order to optimize the set-up of the ADCP for a 
particular measurement, and to evaluate the quality of that measurement.  
Districts using or planning to use ADCP's are encouraged to develop 
expertise in the use of this device.  Parties making discharge 
measurements using the ADCP should include a person who: (1) attended 
basic training in the use of the ADCP's; (2) is familiar with the basic 
principals of ADCP operation; (3) knows the principal sources of ADCP 
velocity and discharge measurement errors and how to evaluate and 
minimize them; and (4) is knowledgeable about the Transect Software.  
This information can be gained by experience, manufacturer's manuals, 
other relevant literature, and training at a U.S. Geological Survey 
sponsored workshop.  A practical alternative training method would be 
working with experienced ADCP operators as on-the-job trainees in a 
mentoring environment.  OSW can provide information on qualified 


Measurements made with the ADCP should be documented on the standard 
form 9-275 C or G, (all applicable information) and on the attached ADCP 
Discharge Measurement Notes form or a modified ADCP form which 
documents individual transect data.  The ADCP configuration file and 
the raw data file for each of the transects making up the measurement 
must be archived. Districts may wish to archive additional files or 
data.  All ADCP discharge measurements must be reviewed by a qualified 

                                   Thomas H. Yorke
                                   Chief, Office of Surface Water