Hydrometry — Guidelines for the application of acoustic velocity meters using the Doppler and echo correlation methods

ISO 15769:2010 provides guidelines on the principles of operation and the selection and use of Doppler-based and echo correlation velocity meters for continuous-flow gauging. ISO 15769:2010 is applicable to channel flow determination in open channels and partially filled pipes using one or more meters located at fixed points in the cross-section.

Hydrométrie — Lignes directrices pour l'application des compteurs de vitesse ultrasoniques fixes utilisant l'effet Doppler et la corrélation d'échos

Hidrometrija - Smernice za uporabo akustičnih merilnikov hitrosti s pomočjo Dopplerjeve in korelacijske metode z odmevom

Ta mednarodni standard navaja smernice glede načel delovanja ter izbire in uporabe merilnikov hitrosti s pomočjo Dopplerjeve in korelacijske metode z odmevom za merjenje neprekinjenega pretoka.  Ta mednarodni standard se uporablja za ugotavljanje pretoka kanala v odprtih kanalih in delno napolnjenih ceveh z uporabo enega ali več merilnikov, ki so nameščeni na fiksnih točkah v prerezu.

General Information

Status
Published
Publication Date
05-Apr-2010
Current Stage
9093 - International Standard confirmed
Start Date
28-Sep-2015
Completion Date
08-Jun-2021

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INTERNATIONAL ISO
STANDARD 15769
First edition
2010-04-15
Hydrometry — Guidelines for the
application of acoustic velocity meters
using the Doppler and echo correlation
methods
Hydrométrie — Lignes directrices pour l'application des compteurs de
vitesse ultrasoniques fixes utilisant l'effet Doppler et la corrélation
d'échos
Reference number
ISO 15769:2010(E)
ISO 2010
---------------------- Page: 1 ----------------------
ISO 15769:2010(E)
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but

shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation

parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In

the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

COPYRIGHT PROTECTED DOCUMENT
© ISO 2010

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
ISO copyright office
Case postale 56  CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2010 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 15769:2010(E)
Contents Page

Foreword .............................................................................................................................................................v

1 Scope......................................................................................................................................................1

2 Normative references............................................................................................................................1

3 Terms, definitions and abbreviated terms..........................................................................................1

3.1 Terms and definitions ...........................................................................................................................1

3.2 Abbreviated terms .................................................................................................................................3

4 Principles of operation of the techniques...........................................................................................3

4.1 Ultrasonic Doppler ................................................................................................................................3

4.2 Operating techniques............................................................................................................................5

4.3 Bed-mounted Doppler systems ...........................................................................................................6

4.4 Side-looking/horizontal ADCPs ...........................................................................................................6

4.5 Acoustic (echo) correlation method....................................................................................................8

4.6 Velocity-index ratings .........................................................................................................................11

5 Factors affecting operation and accuracy........................................................................................11

5.1 General .................................................................................................................................................11

5.2 Characteristics of the instrument ......................................................................................................11

5.3 Channel and water characteristics ....................................................................................................16

5.4 Effect of weed ......................................................................................................................................20

6 Site selection .......................................................................................................................................20

6.1 General .................................................................................................................................................20

6.2 General site requirements for Dopplers and echo correlation devices.........................................20

6.3 Bed-mounted ultrasonic Doppler and echo correlation devices ...................................................21

6.4 Side-lookers .........................................................................................................................................22

7 Measurements .....................................................................................................................................22

7.1 Velocity.................................................................................................................................................22

7.2 Water level............................................................................................................................................23

7.3 Determination of cross-sectional area..............................................................................................23

8 Installation, operation and maintenance...........................................................................................23

8.1 Installation considerations.................................................................................................................23

8.2 General maintenance considerations ...............................................................................................25

9 Calibration, evaluation and verification ............................................................................................26

9.1 General .................................................................................................................................................26

9.2 Calibration and performance checking.............................................................................................26

10 Determination of discharge................................................................................................................27

10.1 General .................................................................................................................................................27

10.2 Velocity-index ratings .........................................................................................................................28

11 Uncertainties in discharge determinations.......................................................................................32

11.1 General .................................................................................................................................................32

11.2 Definition of uncertainty .....................................................................................................................32

11.3 General expectations of performance...............................................................................................33

11.4 Methodology of estimating the uncertainty in discharge determination ......................................33

12 Points to consider when selecting equipment.................................................................................38

Annex A (informative) Selection considerations for ultrasonic Doppler and echo correlation

devices..................................................................................................................................................39

Annex B (informative) Practical considerations ............................................................................................41

© ISO 2010 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 15769:2010(E)

Annex C (informative) Introduction to measurement uncertainty................................................................45

Annex D (informative) Performance guide for hydrometric equipment for use in technical

standards..............................................................................................................................................53

Annex E (informative) Sample questionnaire — Doppler- and echo-correlation-based flowmeters........56

Bibliography ......................................................................................................................................................61

iv © ISO 2010 – All rights reserved
---------------------- Page: 4 ----------------------
ISO 15769:2010(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 15769 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 1, Velocity

area methods.

This first edition of ISO 15769 cancels and replaces ISO/TS 15769:2000, which has been technically revised.

© ISO 2010 – All rights reserved v
---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 15769:2010(E)
Hydrometry — Guidelines for the application of acoustic
velocity meters using the Doppler and echo correlation
methods
1 Scope

This International Standard provides guidelines on the principles of operation and the selection and use of

Doppler-based and echo correlation velocity meters for continuous-flow gauging.

This International Standard is applicable to channel flow determination in open channels and partially filled

pipes using one or more meters located at fixed points in the cross-section.

NOTE A limitation of the techniques is that measurement is made of the velocity of particles, other reflectors or

disturbances.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document applies.
ISO/TS 25377:2007, Hydrometric uncertainty guidance (HUG)
ISO 772, Hydrometry — Vocabulary and symbols
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 772 and the following apply.

3.1.1
beam angle

mounting angle of the acoustic transducer relative to the normalized profiling direction

NOTE Different beam angles will be suitable for different applications.
3.1.2
beam width

width of the acoustic signal transmitted, in degrees (°), from the centre of the transducer

NOTE This, coupled with the side lobe of the acoustic signal, will affect the suitability of a particular instrument for its

application, based on the mounting location and the distance of the water volume measured from the sensor.

© ISO 2010 – All rights reserved 1
---------------------- Page: 6 ----------------------
ISO 15769:2010(E)
3.1.3
bed-mounted device

upward-looking Doppler or echo correlation device that measures velocities within a beam looking upwards at

an angle through the water column
3.1.4
bin
depth cell

portion of the water sampled by the instrument at a known distance and orientation from the transducers

NOTE The instrument determines the velocity in each cell.
3.1.5
blanking distance

portion of water close to the instrument that is not sampled by Doppler technology

NOTE 1 This is left blank to allow the transducer to stop “ringing” before it receives reflected signals.

NOTE 2 It is also used to avoid the instrument sampling velocity in the zone of flow interference created close to, and

by, the instrument.
3.1.6
broad-band Doppler

instrument that records velocity at set distances from the sensor (see range-gated Doppler, 3.1.11) using

coded acoustic pulses to make multiple velocity measurements from a single pulse pair (ping)

3.1.7
continuous Doppler

simple type of Doppler instrument that measures the Doppler shift of all the particles within the range of the

beam, taking the frequency with the largest peak as the average
3.1.8
downward-looking device

instrument that can be deployed floating on the water surface looking down into the water column

3.1.9
echo (cross) correlation

acoustic technique for recognizing echo images that can be used to determine the velocity of particles moving

in the flowing water
3.1.10
profiling Doppler

Doppler instrument that discriminates between signals from reflectors at different distances from the sensor

and uses this information to moderate the estimate of average velocity
3.1.11
range-gated Doppler

sophisticated Doppler instrument that records particle velocities at pre-set distances from the sensor

NOTE Some instruments can produce velocity profiles along the length of the beam, while others just log

measurements from one or more pre-defined cells.
3.1.12
side lobe

most transducers that are developed using current technology have parasitic side lobes that are emitted off

the main acoustic beam

NOTE The side-lobe effect needs to be allowed for in the design and operation of the instrument.

2 © ISO 2010 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 15769:2010(E)
3.1.13
side-looker
Doppler usually mounted on the side of the channel
3.1.14
stage
water level measured relative to a fixed datum
EXAMPLE The level of the lowest point in the channel.
3.1.15
upward-looking device
bed-mounted instrument that looks up through the water column
3.2 Abbreviated terms
Abbreviation Meaning Notes
ADCP acoustic Doppler current profiler
ADP acoustic Doppler profiler
This is a registered trademark of Sontek/YSI.

ADVM acoustic Doppler velocity meter Term used to describe a profiling acoustic Doppler

instrument velocity.
ADVP acoustic Doppler velocity profiler Alternative acronym and name for ADCP.
H-ADCP horizontal ADCP Side/bank-mounted acoustic Doppler velocity profiler.
H-ADVM horizontal ADVM Side/bank-mounted acoustic Doppler velocity meter.
4 Principles of operation of the techniques
4.1 Ultrasonic Doppler

The method of velocity measurement used is based upon a phenomenon first identified by Christian Doppler

in 1843. The principle of “Doppler shift” describes the difference, or shift, which occurs in the frequency of

emitted sound waves as they are reflected back from a moving body.

The sensors of Doppler systems normally contain a transmitting and a receiving device (see Figure 1). A

sound wave of high frequency (F ) is transmitted into the flow of water and intercepted and reflected back at a

different frequency by tiny particles or air bubbles (reflectors). A typical reflector n produces a frequency shift

F . The “shift” between transmitted and reflected frequencies is proportional to the movement of particles

relative to the position of the sound source (i.e. the sensor).

1) Sontek/YSI is an example of a suitable product available commercially. This information is given for the convenience

of users of this document and does not constitute an endorsement by ISO of this product.

© ISO 2010 – All rights reserved 3
---------------------- Page: 8 ----------------------
ISO 15769:2010(E)
Key
1 Doppler sensor
2 water surface
3 channel bed
a, b and c particulates
F frequency of transmitted sound pulse
F , F and F frequency of sound pulses reflected from particulates a, b and c
a b c
V , V and V velocity of particulates a, b and c
a b c
. angle between the horizontal and the angle of the sound beam
Figure 1 — Principle of Doppler ultrasonic flow measurement

Doppler shift only occurs if there is relative movement between the transmitted sound source and the reflected

sound source along the acoustic beam (but not if it is perpendicular to it). The velocity of the moving reflector n

can be calculated from
a) the magnitude of the Doppler shift,
b) the angle between the transmitted beam and the direction of movement, and
c) the velocity of sound in water.
It can be shown that
v = F • c/2F cos .
n dn s n
where
F is the Doppler frequency shift produced by reflector n;
F is the frequency of sound with no movement;
v is the relative velocity between the transmitted sound source and reflector n;
c is the velocity of sound in water;

. is the angle between the reflector's line of motion (the assumed flow path) and the direction of the

acoustic beam.
4 © ISO 2010 – All rights reserved
---------------------- Page: 9 ----------------------
ISO 15769:2010(E)

A Doppler velocity meter measures the resultant frequency shift produced by a large number of reflectors, of

which reflector n is typical, and from that computes a mean velocity. It is the velocity of moving particles, and

not water velocity, which is measured. By including the velocity of many particles, it aims to make an estimate

of the mean water velocity of the volume sampled by the acoustic beam. Although the particles, if small, will

travel at almost the same speed as the water, sampling errors may occur depending on the spatial and

velocity distribution of the particles.

The cross-sectional area is also required to apply the velocity-area calculation of discharge. Most systems

incorporate a water-level sensor, and combining the water depth with knowledge of the cross-sectional profile

allows the flow to be calculated.
4.2 Operating techniques
4.2.1 Introduction

All Dopplers fit into one of four general categories, based upon the method by which the measurements are

made:
a) continuous wave Dopplers;
b) pulsed incoherent profiling Dopplers (including narrow band);
c) pulse-to-pulse coherent;
d) spread spectrum or broad band.

The last three of these four categories are all range gated. Range gating breaks the signal into successive

segments and processes each segment independently of the others. This allows the instrument to measure

the profile of the velocity at different distances from the instrument, with precise knowledge of the location of

each velocity measurement. Reference should be made to the manufacturer's instrument manual to determine

the type of instrument in use.
4.2.2 Continuous wave Dopplers

Pulse incoherent or continuous Dopplers are the simplest type of Doppler system. A continuous Doppler

transmits a continuous signal with one transducer, while receiving the reflected signal with a separate

transducer. The instrument measures the Doppler shift, which is used to calculate the velocity of the particles

along the path of the acoustic beam. The instrument takes an average of the measured velocities calculated

from the frequency and the strength of the loudest reflected signals. The instrument cannot determine the

precise location within the water column. In some situations, this simplicity does not cause any problems but,

in channels where the sediment distribution is uneven, the loudest signal may not represent the average

velocity in the channel. In addition, in channels with a heavy sediment load, most of the signal would be

reflected back before fully penetrating the water column. Thus, the loudest signal would be from close to the

instrument and would not be representative of the average velocity in the channel.

4.2.3 Pulse incoherent

Incoherent Doppler or profiling systems are more sophisticated than continuous wave Dopplers, in that they

take into account the distance travelled by the reflected signals when calculating the average velocity. An

incoherent Doppler transmits a single pulse of sound and measures the Doppler shift, which is used to

determine the velocity of the particles along the path of the acoustic beam. Based upon the elapsed time since

the pulse was transmitted, and the speed of sound in water, the exact location of the velocity measurement is

known. By range gating the return signal at different times, the profile of velocity with the distance away from

the instrument can be determined.
© ISO 2010 – All rights reserved 5
---------------------- Page: 10 ----------------------
ISO 15769:2010(E)
4.2.4 Pulse-to-pulse coherent

Coherent Doppler systems follow many of the same measurement principles as incoherent Doppler systems,

but use a different method for determining the Doppler shift. Coherent systems transmit one relatively short

pulse, record the return signal and then transmit a second short pulse, when the return from the first pulse is

no longer detectable. The instrument measures the phase differences between the two returns and uses this

to calculate the Doppler shift. Signals too close to the instrument are rejected.

4.2.5 Spread spectrum (broad band)

Like coherent systems, broad-band Dopplers transmit two pulses and look at the phase change of the return

from successive pulses. However, with broad-band systems, both acoustic pulses are within the profiling

range at the same time. The broad-band acoustic pulse is complex, it has a code superimposed on the wave

form. The code is imposed on the wave form by reversing the phase and creating a pseudo-random code

within the wave form. This pseudo-random code allows many independent samples to be collected from a

single sound pulse. Because of the complexity of the pulse, the processing is slower than in a narrow-band

system. However, multiple independent samples are obtained from each ping.
4.2.6 Range gating

The range gating method breaks the signal into successive segments and processes each segment

independently of the others. Side-looking/horizontal ADCPs use this approach, as do several of the more

sophisticated bed-mounted devices.
4.3 Bed-mounted Doppler systems

Bed-mounted Doppler systems include all four types of Doppler instrument. They are normally used in smaller

channels, for example up to 5 m wide and 5 m deep, where they are often practical and easy to install.

However, this does not mean they cannot be used in larger channels, even though it may be difficult to install

bed-mounted instruments in particularly deep channels. If siltation is a problem, it may be possible to mount

such devices on a raised platform or on the channel sides.
4.4 Side-looking/horizontal ADCPs

These instruments are usually fixed to the side of the channel and look across the channel to determine

velocities in one horizontal layer across the full width, or a portion of the width, of the cross-section (excluding

the blanking distance). Most systems consist of two transducers, one sending a beam diagonally across the

channel in an upstream direction and the other diagonally across the channel in a downstream direction

[see Figures 2 a) and 2 b)]. A fixed, side-looking ADCP does not estimate velocity throughout the full channel

cross-section. With a known orientation of the transducers, each beam can be divided into an equal number of

cells or bins and the component average velocity in the x-, y- and resultant directions can be determined for

each cell. An integrated cell will give an average velocity, or individual cell velocities can then be averaged to

determine the index velocity/measured velocity for the sampled length for the full distance sampled, or by

selecting cells for a portion of the length. The mean velocity in the x-direction, i.e. at right angles to the

measuring cross-section or parallel with the assumed direction of flow, is usually used to derive the

velocity-index rating. Effectively, the instrument looks at a single horizontal layer across the channel

(see-Figure 3). This layer is divided into one or more sample cells or bins and the average velocity is

computed for each. The operator can usually select the size and position of these measurement cells.

6 © ISO 2010 – All rights reserved
---------------------- Page: 11 ----------------------
ISO 15769:2010(E)
Key
1 bank of channel
2 beams
3 direction of flow
a) Plan view
b) Side view
Key
1 instrument 4 channel bed
2 first cell 5 last cell
3 water surface H height of water above cell

Figure 2 — Diagram illustrating a typical H-ADCP/side-looker beam and cell arrangement

© ISO 2010 – All rights reserved 7
---------------------- Page: 12 ----------------------
ISO 15769:2010(E)

In this example, the beam is sampling the majority of the width of the channel. The average velocity in each

cell is that averaged over the full beam width in the cell.

Figure 3 — Sketch illustrating the channel cross-section sampled by a side-looking ADCP,

illustrating the spread of the beam, and the measurement cells sampled

Velocities close to the instrument typically remain unmeasured. This is for the following two reasons.

a) The area near the transducer (blank after transmit) is left blank to allow the transducer to stop “ringing”

before it receives reflected signals. The minimum blanking distance can be obtained from the

manufacturer's literature.

b) To avoid measuring in the zone of turbulence created by the instrument itself.

4.5 Acoustic (echo) correlation method

The echo (cross) correlation velocity meter is very similar to a bed-mounted ultrasonic Doppler in size and

application. However, even though it is dependent on transmitted sound pulses being reflected back from

moving particles, it works on somewhat different principles. An ultrasonic transducer transmits a short

ultrasonic pulse (or pulse code) into the water. These pulses are reflected by particles or air bubbles. The

reflected ultrasonic echo from the first pulse is received as a characteristic pattern. This is digitized and stored

as the first scan of the dated echo pattern. About 0,4 ms to 4 ms later, another ultrasonic pulse is transmitted

and the incoming echo patterns are digitized and stored. This is the second scan pattern. Using the travel time

difference between the transmission and reception time, the position of the particles in the flow cross-section

can be determined. By means of cross-correlation, the echo patterns are checked within different time

windows for agreement. The cross-correlation also delivers the temporal movement of the characteristic

pattern in the second scan. This temporal movement of the pattern under consideration can be directly

converted to the velocity of flow for this particular beam. The process is repeated a large number of times per

second and single velocities at different distances are computed in real time. The instrument effectively

divides the water column in front of it into a number of cells, so it is possible to accurately determine the

velocity profile in the vertical (see Figures 4, 5 and 6).
8 © ISO 2010 – All rights reserved
---------------------- Page: 13 ----------------------
ISO 15769:2010(E)
Key
1 scan windows (cells) 5 water surface
2 water level sensor V velocity at cell a
3 velocity sensor V maximum velocity
max
4 channel bed
Figure 4 — Sketch illustrating an echo correlation velocity meter
Key
1 E1 to E4 = reflection particle 6 measuring window 1
2 scan 1 7 sensor
3 measuring windows 4 to 16 8 water surface
4 measuring window 3 9 bed level
5 measuring window 2

Figure 5 — Sketches illustrating the principles of the echo correlation velocity meter (continued)

© ISO 2010 – All rights reserved 9
---------------------- Page: 14 ----------------------
ISO 15769:2010(E)
1 E1 to E4 = reflection particle
2 scan 2
3 measuring windows 4 to 16
4 measuring window 3
5 measuring window 2
6 measuring window 1
7 sensor
8 water surface
9 bed level

Figure 5 — Sketches illustrating the principles of the echo correlation velocity meter

Key
1 signal reception, 1st scan 4 measuring window 3
2 signal reception, 2nd scan 5 measuring window 2
3 signal evaluation 6 measuring window 1

For nth window: E is the echo in window n, t is the time between echoes in window n and n is the window number.

n n
Figure 6 — Sketch illustrating the principles of the echo (cross) corr
...

SLOVENSKI STANDARD
SIST ISO 15769:2015
01-februar-2015
+LGURPHWULMD6PHUQLFH]DXSRUDERDNXVWLþQLKPHULOQLNRYKLWURVWLVSRPRþMR
'RSSOHUMHYHLQNRUHODFLMVNHPHWRGH]RGPHYRP

Hydrometry - Guidelines for the application of acoustic velocity meters using the Doppler

and echo correlation methods
Hydrométrie - Lignes directrices pour l'application des compteurs de vitesse
ultrasoniques fixes utilisant l'effet Doppler et la corrélation d'échos
Ta slovenski standard je istoveten z: ISO 15769:2010
ICS:
17.120.20 Pretok v odprtih kanalih Flow in open channels
SIST ISO 15769:2015 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST ISO 15769:2015
---------------------- Page: 2 ----------------------
SIST ISO 15769:2015
INTERNATIONAL ISO
STANDARD 15769
First edition
2010-04-15
Hydrometry — Guidelines for the
application of acoustic velocity meters
using the Doppler and echo correlation
methods
Hydrométrie — Lignes directrices pour l'application des compteurs de
vitesse ultrasoniques fixes utilisant l'effet Doppler et la corrélation
d'échos
Reference number
ISO 15769:2010(E)
ISO 2010
---------------------- Page: 3 ----------------------
SIST ISO 15769:2015
ISO 15769:2010(E)
PDF disclaimer

This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but

shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In

downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat

accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.

Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation

parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In

the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

COPYRIGHT PROTECTED DOCUMENT
© ISO 2010

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
ISO copyright office
Case postale 56  CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2010 – All rights reserved
---------------------- Page: 4 ----------------------
SIST ISO 15769:2015
ISO 15769:2010(E)
Contents Page

Foreword .............................................................................................................................................................v

1 Scope......................................................................................................................................................1

2 Normative references............................................................................................................................1

3 Terms, definitions and abbreviated terms..........................................................................................1

3.1 Terms and definitions ...........................................................................................................................1

3.2 Abbreviated terms .................................................................................................................................3

4 Principles of operation of the techniques...........................................................................................3

4.1 Ultrasonic Doppler ................................................................................................................................3

4.2 Operating techniques............................................................................................................................5

4.3 Bed-mounted Doppler systems ...........................................................................................................6

4.4 Side-looking/horizontal ADCPs ...........................................................................................................6

4.5 Acoustic (echo) correlation method....................................................................................................8

4.6 Velocity-index ratings .........................................................................................................................11

5 Factors affecting operation and accuracy........................................................................................11

5.1 General .................................................................................................................................................11

5.2 Characteristics of the instrument ......................................................................................................11

5.3 Channel and water characteristics ....................................................................................................16

5.4 Effect of weed ......................................................................................................................................20

6 Site selection .......................................................................................................................................20

6.1 General .................................................................................................................................................20

6.2 General site requirements for Dopplers and echo correlation devices.........................................20

6.3 Bed-mounted ultrasonic Doppler and echo correlation devices ...................................................21

6.4 Side-lookers .........................................................................................................................................22

7 Measurements .....................................................................................................................................22

7.1 Velocity.................................................................................................................................................22

7.2 Water level............................................................................................................................................23

7.3 Determination of cross-sectional area..............................................................................................23

8 Installation, operation and maintenance...........................................................................................23

8.1 Installation considerations.................................................................................................................23

8.2 General maintenance considerations ...............................................................................................25

9 Calibration, evaluation and verification ............................................................................................26

9.1 General .................................................................................................................................................26

9.2 Calibration and performance checking.............................................................................................26

10 Determination of discharge................................................................................................................27

10.1 General .................................................................................................................................................27

10.2 Velocity-index ratings .........................................................................................................................28

11 Uncertainties in discharge determinations.......................................................................................32

11.1 General .................................................................................................................................................32

11.2 Definition of uncertainty .....................................................................................................................32

11.3 General expectations of performance...............................................................................................33

11.4 Methodology of estimating the uncertainty in discharge determination ......................................33

12 Points to consider when selecting equipment.................................................................................38

Annex A (informative) Selection considerations for ultrasonic Doppler and echo correlation

devices..................................................................................................................................................39

Annex B (informative) Practical considerations ............................................................................................41

© ISO 2010 – All rights reserved iii
---------------------- Page: 5 ----------------------
SIST ISO 15769:2015
ISO 15769:2010(E)

Annex C (informative) Introduction to measurement uncertainty................................................................45

Annex D (informative) Performance guide for hydrometric equipment for use in technical

standards..............................................................................................................................................53

Annex E (informative) Sample questionnaire — Doppler- and echo-correlation-based flowmeters........56

Bibliography ......................................................................................................................................................61

iv © ISO 2010 – All rights reserved
---------------------- Page: 6 ----------------------
SIST ISO 15769:2015
ISO 15769:2010(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 15769 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 1, Velocity

area methods.

This first edition of ISO 15769 cancels and replaces ISO/TS 15769:2000, which has been technically revised.

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INTERNATIONAL STANDARD ISO 15769:2010(E)
Hydrometry — Guidelines for the application of acoustic
velocity meters using the Doppler and echo correlation
methods
1 Scope

This International Standard provides guidelines on the principles of operation and the selection and use of

Doppler-based and echo correlation velocity meters for continuous-flow gauging.

This International Standard is applicable to channel flow determination in open channels and partially filled

pipes using one or more meters located at fixed points in the cross-section.

NOTE A limitation of the techniques is that measurement is made of the velocity of particles, other reflectors or

disturbances.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document applies.
ISO/TS 25377:2007, Hydrometric uncertainty guidance (HUG)
ISO 772, Hydrometry — Vocabulary and symbols
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 772 and the following apply.

3.1.1
beam angle

mounting angle of the acoustic transducer relative to the normalized profiling direction

NOTE Different beam angles will be suitable for different applications.
3.1.2
beam width

width of the acoustic signal transmitted, in degrees (°), from the centre of the transducer

NOTE This, coupled with the side lobe of the acoustic signal, will affect the suitability of a particular instrument for its

application, based on the mounting location and the distance of the water volume measured from the sensor.

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3.1.3
bed-mounted device

upward-looking Doppler or echo correlation device that measures velocities within a beam looking upwards at

an angle through the water column
3.1.4
bin
depth cell

portion of the water sampled by the instrument at a known distance and orientation from the transducers

NOTE The instrument determines the velocity in each cell.
3.1.5
blanking distance

portion of water close to the instrument that is not sampled by Doppler technology

NOTE 1 This is left blank to allow the transducer to stop “ringing” before it receives reflected signals.

NOTE 2 It is also used to avoid the instrument sampling velocity in the zone of flow interference created close to, and

by, the instrument.
3.1.6
broad-band Doppler

instrument that records velocity at set distances from the sensor (see range-gated Doppler, 3.1.11) using

coded acoustic pulses to make multiple velocity measurements from a single pulse pair (ping)

3.1.7
continuous Doppler

simple type of Doppler instrument that measures the Doppler shift of all the particles within the range of the

beam, taking the frequency with the largest peak as the average
3.1.8
downward-looking device

instrument that can be deployed floating on the water surface looking down into the water column

3.1.9
echo (cross) correlation

acoustic technique for recognizing echo images that can be used to determine the velocity of particles moving

in the flowing water
3.1.10
profiling Doppler

Doppler instrument that discriminates between signals from reflectors at different distances from the sensor

and uses this information to moderate the estimate of average velocity
3.1.11
range-gated Doppler

sophisticated Doppler instrument that records particle velocities at pre-set distances from the sensor

NOTE Some instruments can produce velocity profiles along the length of the beam, while others just log

measurements from one or more pre-defined cells.
3.1.12
side lobe

most transducers that are developed using current technology have parasitic side lobes that are emitted off

the main acoustic beam

NOTE The side-lobe effect needs to be allowed for in the design and operation of the instrument.

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3.1.13
side-looker
Doppler usually mounted on the side of the channel
3.1.14
stage
water level measured relative to a fixed datum
EXAMPLE The level of the lowest point in the channel.
3.1.15
upward-looking device
bed-mounted instrument that looks up through the water column
3.2 Abbreviated terms
Abbreviation Meaning Notes
ADCP acoustic Doppler current profiler
ADP acoustic Doppler profiler
This is a registered trademark of Sontek/YSI.

ADVM acoustic Doppler velocity meter Term used to describe a profiling acoustic Doppler

instrument velocity.
ADVP acoustic Doppler velocity profiler Alternative acronym and name for ADCP.
H-ADCP horizontal ADCP Side/bank-mounted acoustic Doppler velocity profiler.
H-ADVM horizontal ADVM Side/bank-mounted acoustic Doppler velocity meter.
4 Principles of operation of the techniques
4.1 Ultrasonic Doppler

The method of velocity measurement used is based upon a phenomenon first identified by Christian Doppler

in 1843. The principle of “Doppler shift” describes the difference, or shift, which occurs in the frequency of

emitted sound waves as they are reflected back from a moving body.

The sensors of Doppler systems normally contain a transmitting and a receiving device (see Figure 1). A

sound wave of high frequency (F ) is transmitted into the flow of water and intercepted and reflected back at a

different frequency by tiny particles or air bubbles (reflectors). A typical reflector n produces a frequency shift

F . The “shift” between transmitted and reflected frequencies is proportional to the movement of particles

relative to the position of the sound source (i.e. the sensor).

1) Sontek/YSI is an example of a suitable product available commercially. This information is given for the convenience

of users of this document and does not constitute an endorsement by ISO of this product.

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Key
1 Doppler sensor
2 water surface
3 channel bed
a, b and c particulates
F frequency of transmitted sound pulse
F , F and F frequency of sound pulses reflected from particulates a, b and c
a b c
V , V and V velocity of particulates a, b and c
a b c
. angle between the horizontal and the angle of the sound beam
Figure 1 — Principle of Doppler ultrasonic flow measurement

Doppler shift only occurs if there is relative movement between the transmitted sound source and the reflected

sound source along the acoustic beam (but not if it is perpendicular to it). The velocity of the moving reflector n

can be calculated from
a) the magnitude of the Doppler shift,
b) the angle between the transmitted beam and the direction of movement, and
c) the velocity of sound in water.
It can be shown that
v = F • c/2F cos .
n dn s n
where
F is the Doppler frequency shift produced by reflector n;
F is the frequency of sound with no movement;
v is the relative velocity between the transmitted sound source and reflector n;
c is the velocity of sound in water;

. is the angle between the reflector's line of motion (the assumed flow path) and the direction of the

acoustic beam.
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A Doppler velocity meter measures the resultant frequency shift produced by a large number of reflectors, of

which reflector n is typical, and from that computes a mean velocity. It is the velocity of moving particles, and

not water velocity, which is measured. By including the velocity of many particles, it aims to make an estimate

of the mean water velocity of the volume sampled by the acoustic beam. Although the particles, if small, will

travel at almost the same speed as the water, sampling errors may occur depending on the spatial and

velocity distribution of the particles.

The cross-sectional area is also required to apply the velocity-area calculation of discharge. Most systems

incorporate a water-level sensor, and combining the water depth with knowledge of the cross-sectional profile

allows the flow to be calculated.
4.2 Operating techniques
4.2.1 Introduction

All Dopplers fit into one of four general categories, based upon the method by which the measurements are

made:
a) continuous wave Dopplers;
b) pulsed incoherent profiling Dopplers (including narrow band);
c) pulse-to-pulse coherent;
d) spread spectrum or broad band.

The last three of these four categories are all range gated. Range gating breaks the signal into successive

segments and processes each segment independently of the others. This allows the instrument to measure

the profile of the velocity at different distances from the instrument, with precise knowledge of the location of

each velocity measurement. Reference should be made to the manufacturer's instrument manual to determine

the type of instrument in use.
4.2.2 Continuous wave Dopplers

Pulse incoherent or continuous Dopplers are the simplest type of Doppler system. A continuous Doppler

transmits a continuous signal with one transducer, while receiving the reflected signal with a separate

transducer. The instrument measures the Doppler shift, which is used to calculate the velocity of the particles

along the path of the acoustic beam. The instrument takes an average of the measured velocities calculated

from the frequency and the strength of the loudest reflected signals. The instrument cannot determine the

precise location within the water column. In some situations, this simplicity does not cause any problems but,

in channels where the sediment distribution is uneven, the loudest signal may not represent the average

velocity in the channel. In addition, in channels with a heavy sediment load, most of the signal would be

reflected back before fully penetrating the water column. Thus, the loudest signal would be from close to the

instrument and would not be representative of the average velocity in the channel.

4.2.3 Pulse incoherent

Incoherent Doppler or profiling systems are more sophisticated than continuous wave Dopplers, in that they

take into account the distance travelled by the reflected signals when calculating the average velocity. An

incoherent Doppler transmits a single pulse of sound and measures the Doppler shift, which is used to

determine the velocity of the particles along the path of the acoustic beam. Based upon the elapsed time since

the pulse was transmitted, and the speed of sound in water, the exact location of the velocity measurement is

known. By range gating the return signal at different times, the profile of velocity with the distance away from

the instrument can be determined.
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4.2.4 Pulse-to-pulse coherent

Coherent Doppler systems follow many of the same measurement principles as incoherent Doppler systems,

but use a different method for determining the Doppler shift. Coherent systems transmit one relatively short

pulse, record the return signal and then transmit a second short pulse, when the return from the first pulse is

no longer detectable. The instrument measures the phase differences between the two returns and uses this

to calculate the Doppler shift. Signals too close to the instrument are rejected.

4.2.5 Spread spectrum (broad band)

Like coherent systems, broad-band Dopplers transmit two pulses and look at the phase change of the return

from successive pulses. However, with broad-band systems, both acoustic pulses are within the profiling

range at the same time. The broad-band acoustic pulse is complex, it has a code superimposed on the wave

form. The code is imposed on the wave form by reversing the phase and creating a pseudo-random code

within the wave form. This pseudo-random code allows many independent samples to be collected from a

single sound pulse. Because of the complexity of the pulse, the processing is slower than in a narrow-band

system. However, multiple independent samples are obtained from each ping.
4.2.6 Range gating

The range gating method breaks the signal into successive segments and processes each segment

independently of the others. Side-looking/horizontal ADCPs use this approach, as do several of the more

sophisticated bed-mounted devices.
4.3 Bed-mounted Doppler systems

Bed-mounted Doppler systems include all four types of Doppler instrument. They are normally used in smaller

channels, for example up to 5 m wide and 5 m deep, where they are often practical and easy to install.

However, this does not mean they cannot be used in larger channels, even though it may be difficult to install

bed-mounted instruments in particularly deep channels. If siltation is a problem, it may be possible to mount

such devices on a raised platform or on the channel sides.
4.4 Side-looking/horizontal ADCPs

These instruments are usually fixed to the side of the channel and look across the channel to determine

velocities in one horizontal layer across the full width, or a portion of the width, of the cross-section (excluding

the blanking distance). Most systems consist of two transducers, one sending a beam diagonally across the

channel in an upstream direction and the other diagonally across the channel in a downstream direction

[see Figures 2 a) and 2 b)]. A fixed, side-looking ADCP does not estimate velocity throughout the full channel

cross-section. With a known orientation of the transducers, each beam can be divided into an equal number of

cells or bins and the component average velocity in the x-, y- and resultant directions can be determined for

each cell. An integrated cell will give an average velocity, or individual cell velocities can then be averaged to

determine the index velocity/measured velocity for the sampled length for the full distance sampled, or by

selecting cells for a portion of the length. The mean velocity in the x-direction, i.e. at right angles to the

measuring cross-section or parallel with the assumed direction of flow, is usually used to derive the

velocity-index rating. Effectively, the instrument looks at a single horizontal layer across the channel

(see-Figure 3). This layer is divided into one or more sample cells or bins and the average velocity is

computed for each. The operator can usually select the size and position of these measurement cells.

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Key
1 bank of channel
2 beams
3 direction of flow
a) Plan view
b) Side view
Key
1 instrument 4 channel bed
2 first cell 5 last cell
3 water surface H height of water above cell

Figure 2 — Diagram illustrating a typical H-ADCP/side-looker beam and cell arrangement

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In this example, the beam is sampling the majority of the width of the channel. The average velocity in each

cell is that averaged over the full beam width in the cell.

Figure 3 — Sketch illustrating the channel cross-section sampled by a side-looking ADCP,

illustrating the spread of the beam, and the measurement cells sampled

Velocities close to the instrument typically remain unmeasured. This is for the following two reasons.

a) The area near the transducer (blank after transmit) is left blank to allow the transducer to stop “ringing”

before it receives reflected signals. The minimum blanking distance can be obtained from the

manufacturer's literature.

b) To avoid measuring in the zone of turbulence created by the instrument itself.

4.5 Acoustic (echo) correlation method

The echo (cross) correlation velocity meter is very similar to a bed-mounted ultrasonic Doppler in size and

application. However, even though it is dependent on transmitted sound pulses being reflected back from

moving particles, it works on somewhat different principles. An ultrasonic transducer transmits a short

ultrasonic pulse (or pulse code) into the water. These pulses are reflected by particles or air bubbles. The

reflected ultrasonic echo from the first pulse is received as a characteristic pattern. This is digitized and stored

as the first scan of the dated echo pattern. About 0,4 ms to 4 ms later, another ultrasonic pulse is transmitted

and the incoming echo patterns are digitized and stored. This is the second scan pattern. Using the travel time

difference between the transmission and reception time, the position of the particles in the flow cross-section

can be determined. By means of cross-correlation, the echo patterns are checked within different time

windows for agreement. The cross-correlation also delivers the temporal movement of the characteristic

pattern in the second scan. This temporal movement of the pattern under consideration can be directly

converted to the velocity of flow for this particular beam. The process is repeated a large number of times per

second and single velocities at different distances are computed in real time. The instrument effectively

divides the water column in front of it into a number of cells, so it is possible to accurately determine the

velocity profile in the vertical (see Figures 4, 5 and 6).
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