ISO/TS 24154:2005
(Main)Hydrometry — Measuring river velocity and discharge with acoustic Doppler profilers
Hydrometry — Measuring river velocity and discharge with acoustic Doppler profilers
ISO/TS 24154:2005 gives the principles of operation, construction, maintenance and application of acoustic Doppler profilers to the measurement of velocity and discharge, and discusses calibration and verification issues. It is applicable to open-channel flow measurements with an instrument mounted on a moving vessel. ISO/TS 24154:2005 is not applicable to measurement of liquid flow in small channels or partly-filled pipes using a single Doppler-based flowmeter at a fixed point in the cross section.
Hydrométrie — Mesure de la vitesse et du débit des rivières au moyen de profileurs à effet Doppler
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TECHNICAL ISO/TS
SPECIFICATION 24154
First edition
2005-11-15
Hydrometry — Measuring river velocity
and discharge with acoustic Doppler
profilers
Hydrométrie — Mesure de la vitesse et du débit des rivières au moyen
de profileurs à effet Doppler
Reference number
ISO/TS 24154:2005(E)
©
ISO 2005
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ISO/TS 24154:2005(E)
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ISO/TS 24154:2005(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Background . 2
5 Principles of operation. 2
6 Application of acoustic Doppler profilers to measurement of river discharge. 3
6.1 Instrumentation and equipment requirements . 3
6.2 Making the measurement. 4
6.3 Computing the measurement . 4
7 Factors affecting operation and accuracy . 6
7.1 Characteristics of the acoustic Doppler profiler . 7
7.1.1 Transducers or beams . 7
7.1.2 Size and frequency . 7
7.2 River and channel characteristics . 7
7.3 Operator training and experience . 8
8 Verification . 8
9 Construction. 8
10 Maintenance . 9
Bibliography . 10
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ISO/TS 24154:2005(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
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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.
In other circumstances, particularly when there is an urgent market requirement for such documents, a
technical committee may decide to publish other types of normative document:
— an ISO Publicly Available Specification (ISO/PAS) represents an agreement between technical experts in
an ISO working group and is accepted for publication if it is approved by more than 50 % of the members
of the parent committee casting a vote;
— an ISO Technical Specification (ISO/TS) represents an agreement between the members of a technical
committee and is accepted for publication if it is approved by 2/3 of the members of the committee casting
a vote.
An ISO/PAS or ISO/TS is reviewed after three years in order to decide whether it will be confirmed for a
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confirmed, it is reviewed again after a further three years, at which time it must either be transformed into an
International Standard or be withdrawn.
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/TS 24154 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 5,
Instruments, equipment and data management.
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TECHNICAL SPECIFICATION ISO/TS 24154:2005(E)
Hydrometry — Measuring river velocity and discharge with
acoustic Doppler profilers
1 Scope
Acoustic Doppler profilers are instruments and software packages used to measure water velocity, channel
bathymetry, and river discharge. This Technical Specification gives the principles of operation, construction,
maintenance and application of acoustic Doppler profilers to the measurement of velocity and discharge, and
discusses calibration and verification issues. It is applicable to open-channel flow measurements with an
instrument mounted on a moving vessel.
It is not applicable to measurement of liquid flow in small channels or partly-filled pipes using a single Doppler-
based flowmeter at a fixed point in the cross section.
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 (including any amendments) applies.
ISO 772, Hydrometric determinations — Vocabulary and symbols
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 772 and the following apply.
3.1
Doppler shift
〈general〉 change in frequency of a sound source as it approaches and recedes from an observer
3.2
Doppler shift
〈acoustic Doppler instruments〉 difference or shift in frequency of emitted sound waves as they are reflected
back from moving particles in the water
3.3
Doppler-based flowmeter
class of instruments that uses the principle of Doppler shift to compute water velocity and discharge
NOTE These instruments can be deployed at a fixed point in a cross section or on a moving vessel.
3.4
acoustic Doppler profiler
ADP
instrument that uses the principle of Doppler shift to compute water velocity and discharge
NOTE The instrument is usually mounted on a vessel that transits across a river channel perpendicular to flow.
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ISO/TS 24154:2005(E)
3.5
ping
series of acoustic pulses of a given frequency transmitted by an acoustic Doppler instrument
3.6
ensemble
collection of pings
NOTE Because the measurement results from a single ping have a relatively high error, the results of more than one
ping are usually averaged to obtain a single measurement.
3.7
transect
collection of ensembles from a single pass across a river, lake, or estuary
NOTE When measuring streamflow with an acoustic Doppler profiler, one transect may constitute a single
measurement of discharge.
4 Background
Acoustic Doppler instruments for measuring water velocity have been in use for about 25 years, primarily in
the study of ocean currents and estuaries. In the late 1980s, acoustic Doppler instruments began to be used
[3], [13]
to make velocity measurements from a moving vessel . The early instruments were narrow-band
acoustic Doppler instruments that required deep water (> 3,4 m), which limited their use to deep rivers and
estuaries. In 1992, a more advanced acoustic Doppler instrument, known as a Broadband Acoustic Doppler
Current Profiler, was developed that could be used to measure velocities in shallow waters (as shallow as
1,0 m) with a high degree of vertical resolution (0,10 m).
Throughout the 1990s, acoustic Doppler profilers were continually developed and enhanced by several
manufacturers. The instruments have been refined from very cumbersome and heavy units that were 1 m in
length and weighing as much as 50 kg to compact and light units as small as 14 cm long and weighing 7 kg.
The acoustic Doppler profilers now include advanced acoustic instrumentation designed specifically for use in
rivers and software for real-time and post-processing of river velocity and discharge measurements. Acoustic
Doppler profilers (3.3) are routinely used to measure discharge in estuaries, rivers, and canals where
conventional discharge-measurement techniques are either very expensive or impossible due to stratification
of the flow. They are also routinely used to measure discharge in large rivers, in part because of cost savings
and reduced uncertainties due to smaller changes in discharge during the measurement.
5 Principles of operation
In moving vessel deployments, the acoustic Doppler instrument is mounted to a vessel (usually a motorized
boat) that moves across the water body perpendicular to the current being measured. Water velocities are
measured by the acoustic Doppler instrument, which transmits acoustic pulses along three or four beams at a
constant frequency between 75 kHz to 3 000 kHz. The beams are positioned at precise horizontal angles from
each other (120° for 3-beam instruments and 90° for 4-beam instruments (see Figure 1). The beams are
directed at a known angle from vertical, typically 20° or 30°. The instrument detects and processes echoes
throughout the water column along each beam.
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ISO/TS 24154:2005(E)
Figure 1 — Schematic diagram of an acoustic Doppler instrument with a 4-beam configuration
The difference in frequency (shift) between successive echoes is proportional to the relative velocity between
the acoustic Doppler instrument and suspended material in the water that reflects the pulses back to the
instrument. This frequency shift is known as the Doppler effect. The acoustic Doppler instrument uses the
Doppler effect to compute a water-velocity component along each beam, and the system software computes
water velocity in three directions using trigonometric relations. Velocities are determined at preset intervals
called bins along the acoustic path. The instrument setup parameters can be adjusted to optimize the system
for the river cross section being measured. These parameters include the depth cell size, the number of depth
cells, the number of pings, and velocity reference commands.
The water-velocity measurements incorporate both the true water velocity and the boat velocity. The boat
velocity can be measured by using the Doppler shift of separate acoustic pulses reflected from the river
bottom. This technique, referred to as bottom tracking, is commonly used; it was first used with early sonar to
measure the speed of a moving vessel. In addition to measuring boat velocity, the depth of the river is
estimated from the amplitude of the bottom-track echoes (echoes returned from the bottom). Real-time
differential global-positioning systems (DGPS) provide an alternative technique for measuring the boat velocity.
When the acoustic Doppler instrument is being used to measure discharge, it transmits a series of acoustic
pulses known as pings (3.5). Pings for measuring water velocities are known as water pings, and pings for
measuring the boat velocity are known as bottom-tracking pings. Normally, water pings and bottom-tracking
pings are interleaved during transmission. A group of these interleaved water and bottom-tracking pings are
referred to as an ensemble (3.6). The user sets the number of water and bottom-tracking pings per ensemble.
An ensemble is analogous to one vertical in a conventional discharge measurement. For example, a typical
ensemble is composed of a combination of water pings and bottom-tracking pings. The velocities and depths
measured for each ping are averaged to yield a single velocity profile and depth for each ensemble. In a
conventional discharge measurement, velocity is measured at one point in the vertical when the depth is less
than 0,8 m and two, three or five points in the vertical when the depth is greater than 0,8 m. Depending on its
characteristics, an acoustic Doppler profiler can measure velocities every 0,25 m in the vertical, so that one
ensemble for a vertical 10 m deep may contain as many as 34 velocity measurements.
6 Application of acoustic Doppler profilers to measurement of river discharge
6.1 Instrumentation and equipment requirements
Making discharge measurements with acoustic Doppler profilers requires three main pieces of equipment: the
acoustic instrument/transducer assembly, a vessel for mounting the instrument, and a portable computer. The
instrument includes a pressure case that contains most of the electronics and a transducer assembly (see
Figure 1). The transducer assembly may have a convex or concave assembly. The instruments come in a
variety of sizes, beam configurations, and frequencies depending on the size and characteristics of rivers to
be measured and the type of deployment. The small units are less than 30 cm tall and weigh about 7 kg; large
units are 1 m tall and weigh 50 kg.
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ISO/TS 24154:2005(E)
The type of acoustic Doppler profiler deployed depends on the river being measured. For small rivers, the
system can be mounted in the bottom of a small boat, raft or catamaran. A remote-control motor can power
the boat or a tether can be used to pull the boat and system across the river. Attaching a line from each bank
or traversing the river with a single line from a bridge or cableway can be used for a tethered deployment.
Measurements in large rivers require that the acoustic Doppler profiler be suspended in the water column from
a mounting bracket on a boat powered with a gas or diesel engine. Examples of these two types of
deployment are shown in Figure 2.
The system software processes and displays a large amount of data so a laptop computer with a minimum of
200 MHz processor and > 64 MB of RAM memory is recommended. The computer screen display should be
visible in direct and diffuse sunlight.
Figure 2 — Photographs showing acoustic Doppler profilers deployed on a small,
tethered boat (A) and a power boat (B)
6.2 Making the measurement
A discharge measurement is made with an acoustic Doppler profiler by traversing the river cross section with
the boat or tethered boat. A single traverse, called a transect (3.7), consists of a collection of ensembles.
A typical transect will contain 300 to 1 000 ensembles, whereas a conventional discharge measurement will
typically consist of 25 to 30 verticals. When measuring under relatively steady flow, four transects are made at
each measuring location. Pairs of transects on reciprocal headings are used to minimize any directional bias
that may be present. If the discharge measured on any given transect varies by more than 5 % of the mean
discharge for all the transects, a second set of four transects is made. The mean of the discharges of all
transects is used as the measured discharge. The time required to make four transects with an acoustic
Doppler profiler is typically less than 30 min whereas a conventional discharge measurement may take 1 h to
2 h or more.
With rapidly-changing stage and unsteady flow conditions, a single transect may be used as a discharge
measurement. However, two to four single-transect measurements should be made to help define and verify
the stage-discharge rating at a streamgaging station.
6.3 Computing the measurement
Acoustic Doppler profilers have some limitations for measuring discharge in a river cross section. They cannot
measure
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