ISO 4366:2007
(Main)Hydrometry — Echo sounders for water depth measurements
Hydrometry — Echo sounders for water depth measurements
ISO 4366:2007 provides information concerning the principles of operation, selection and performance criteria for echo sounders used in depth measurements for open-channel flow (and related) measurements. The use of standard terminology is promoted.
Hydrométrie — Sondeurs à écho pour le mesurage de la profondeur de l'eau
General Information
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 4366
Second edition
2007-05-15
Hydrometry — Echo sounders for water
depth measurements
Hydrométrie — Sondeurs à écho pour le mesurage de la profondeur de
l'eau
Reference number
ISO 4366:2007(E)
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ISO 4366:2007(E)
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ISO 4366:2007(E)
Contents Page
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Units of measure . 1
5 Principles of operation . 1
5.1 General . 1
5.2 Theory of operation . 2
5.3 System components . 2
5.4 Non-recording echo sounders . 3
5.5 Analog recording echo sounders . 3
5.6 Digital echo sounders . 4
6 Selection of instrument . 6
6.1 General . 6
6.2 Effect of operating frequency . 6
6.3 Effect of beamwidth . 7
6.4 Type of data display . 8
6.5 Accuracy . 8
6.6 Type of transducer system . 8
7 Instruments performance criteria . 9
7.1 General . 9
7.2 Information to be specified by the user . 9
7.3 Information to be specified by the manufacturer . 9
7.4 Housing . 10
7.5 Additional features . 10
8 Field use of echo sounders . 11
8.1 Calibration . 11
8.2 Interpretation of data . 12
8.3 Precautions . 12
9 Operations manual . 12
Bibliography . 13
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ISO 4366:2007(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 4366 was prepared by Technical Committee ISO/TC 113, Hydrometry, Subcommittee SC 5, Instruments,
equipment and data management.
This second edition cancels and replaces the first edition (ISO 4366:1979), which has been technically revised.
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INTERNATIONAL STANDARD ISO 4366:2007(E)
Hydrometry — Echo sounders for water depth measurements
1Scope
This International Standard provides information concerning the principles of operation, selection and
performance criteria for echo sounders used in depth measurements for open-channel flow (and related)
measurements. The use of standard terminology is promoted.
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
ISO 6420, Liquid flow measurement in open channels — Position fixing equipment for hydrometric boats
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 772 and the following apply.
3.1
tracking window
vertical distance of limited size that follows and automatically centres itself on the depth indicated by the last
received echo
NOTE If the next echo falls within the window, the signal is accepted as correct; if it does not, the signal is rejected. The
purpose of a tracking window is to screen out erroneous readings caused by reflecting materials in the water (fish, debris,
etc.).
4 Units of measure
The units of measurement used in this International Standard are SI units and decibels.
5 Principles of operation
5.1 General
The state-of-the-art of echo sounders is well advanced, and sounders have been put into widespread use for
many different applications. Consequently, a variety of specialized echo sounders have evolved to best meet the
specific requirements of the application. A digital echo sounder with an integrated analog chart generated by a
thermal or inkjet print head is the most common echo sounder used for open-channel applications. Multiple-
transducer systems are in common use by many professional surveyors and the use of single-transducer,
multibeam-swath systems is expanding rapidly.
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5.2 Theory of operation
The echo sounder is an electroacoustic instrument that determines the depth of water by measuring the time
required for a burst of acoustic energy to travel from a transducer to the streambed and reflect back to the
transducer (Figure 1). The travel time of the reflected wave can be converted to distance by use of the following
equation:
vt
d = + k + d (1)
r
2
where
d is the distance from the reference water surface to the streambed;
v is the average velocity of sound in the water column;
t is the travel time of the acoustic energy from the transducer to the bottom and back to the
transducer;
k is the system index constant;
d is the distance from the reference water surface to the transducer (draft).
r
NOTE All distance units are consistent.
The velocity of sound varies with the density and elastic properties of the water, which are primarily a function
of the water temperature and suspended or dissolved constituents (i.e. salinity). Large variations in temperature
and/or salinity with depth are not uncommon. For practical depth measurement with an echo sounder, the
velocity of sound is usually determined by calibration (see 8.1), since measuring and correcting for the actual
variation at each depth interval is difficult.
The travel time of the acoustic energy is recorded either electronically by a digital echo sounder or graphically
by an analog chart echo sounder. The shape, or sharpness, of the reflected acoustic energy pulse plays a
significant role in the accuracy of a depth measurement (Figure 1). The shape and magnitude of the reflected
energy pulse is a function of the acoustic attenuation, background noise and acoustic reflectivity characteristics
of the target.
The system index constant (k) contains all electrical and/or mechanical delays inherent in the measuring
system, including return signal threshold detection variations. The system index constant also contains any
constant correction due to the change in the velocity of sound between the upper surface level and the average
velocity used for the site. Therefore, the draft (d ), set during calibration, is not necessarily the actual draft of the
r
transducer that would be obtained by a physical measurement from the water surface to the transducer, but also
includes corrections for the system index constant determined during on-site calibration.
5.3 System components
The echo sounder consists of two elements: the electronic assembly, which usually includes a display and/or
recording device, and the acoustic assembly commonly called the transducer. The electronic circuitry generates
high frequency electrical energy and provides regulated bursts of this energy to the transducer. When a burst of
energy is released, time is measured until the reflected energy is received, then Equation (1) is solved and the
depth is displayed or recorded.
The transducer is an electroacoustic assembly that acts as a two-way energy conversion device. During
transmission, it converts pulses of electrical energy into pulses of acoustic energy that travel through the water
to the bottom. During reception, it receives the reflected acoustic energy (echo) from the streambed and
converts it into electrical energy for processing by the electronic circuits.
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ISO 4366:2007(E)
Key
1 depthsounder transducer
2draft
3 signal
4 time acoustic pulse is transmitted
5 reduced energy
6 acoustically reflective bottom
2
7 time reflected pulse is received, ( )(depth− k− d )
r
v
8time
[2]
Figure 1 — Illustration of an acoustic depth measurement
5.4 Non-recording echo sounders
The most common type of non-recording echo sounder has a liquid crystal display (LCD) that displays the depth
numerically. Many of these echo sounders also display the return echo graphically and are commonly used as
fish finders by fishermen. The numerical depth determination requires the same processing as a digital echo
sounder (see 5.6). The non-recording echo sounders typically have wider beamwidth transducers and no
calibration adjustments, resulting in a lower accuracy than survey-grade digital echo sounders. Some of the
non-recording echo sounders digitally output the depth to an external device through a serial communications
port.
5.5 Analog recording echo sounders
Traditionally, analog recording echo sounders have used an electric timing motor to rotate a stylus at a constant
speed across heat-sensitive paper. When the stylus passes over the zero contact, it burns a mark on the paper
and simultaneously triggers the release of acoustic energy. The stylus continues to move until reflected acoustic
energy is received at the transducer generating an electrical current that is applied to the stylus to cause it to
burn a mark on the chart again. The stylus continues to rotate until it reaches the zero contact and the cycle is
repeated. As the stylus rotates, the chart is being moved by another motor and the resulting succession of
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marks made by the stylus creates a time-time graph. The stylus speed is adjusted through calibration to equal
the speed at which the acoustic energy travels to the streambed and back, thus the distance between the zero
mark and other marks on the chart are proportional to the distance between the transducer and the streambed.
The speed at which the chart moves is arbitrary so that the chart transit does not necessarily indicate the
distance the boat travelled.
Modern analog recorders, which are often combined with a digital display and output (see 5.6), use a fixed
thermal or inkjet printing head in place of the rotating stylus. This helps reduce the potential synchronization
error and allows electronic filters and processing algorithms to be applied to the data to compensate for the
velocity of sound and allows electronic annotation of the chart. The mass, dimensions and power consumption
of the fixed-head recorders are less than the rotating stylus design.
5.6 Digital echo sounders
5.6.1 General
In the digital echo sounder, acoustic pulses are released at set intervals. When an acoustic pulse is released, a
counter is started and counts the output of an oscillator. When the reflected acoustic energy is received, the
oscillator counts are used to measure the elapsed time and the depth is computed using Equation (1). The
accuracy of the depth measurement is highly dependent on the digitization techniques and filters that are used
to determine what oscillator count represents the streambed.
Digital echo sounders are the most common echo sounders available. They range from non-recording LCD
units to survey-grade echo sounders that usually combine an analog recorder with a numerical display and
digital output.
5.6.2 Digitization techniques
Two digitization techniques are commonly used to screen erroneous data and improve the reliability of the
acoustic data. The most common technique is threshold detection. Threshold detection measures the time from
transmission of the acoustic signal until the energy of the reflected energy exceeds a predetermined threshold
or strength. The remaining acoustic energy is not analysed. The threshold value may be adjusted by the user on
advanced echo sounders, but it is often fixed and not user selectable. A more robust technique, employed on
some survey-grade echo sounders, is peak value detection. Peak value detection analyses all of the reflected
energy and computes the time from acoustic release to the peak of the reflected energy or strongest signal.
Figure 2 illustrates the difference between the two techniques on a sloping bed. The peak value detection
technique produces a measured depth more representative of the centre of the acoustic footprint of the
transducer. The peak value technique can significantly reduce the effective beamwidth of the transducer,
providing a more accurate representation of the streambed directly below the transducer.
Any material such as fish, debris or air bubbles between the transducer and the streambed can reflect acoustic
energy. Peak value detection is less sensitive to these unwanted reflections than threshold detection; however,
nearly all survey-grade echo sounders employ techniques to reduce or eliminate erroneous readings caused by
reflectors in the water column. A tracking window that rejects all signals except those within a given tolerance of
the preceding depth is commonly provided. These reflections from objects in the water column are recorded on
the analog chart in addition to the bottom echo. The analog chart is very valuable for verifying the accuracy of
the digitized depth. Despite the techniques employed in digital echo sounders, erroneous readings are still
common, particularly around obstructions such as bridge piers and sea walls. Depth measurement in such
areas without an analog presentation of the data is not recommended.
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Key
1 sea bottom
2 threshold point, v
P1
3 peak point, v
P2
t time
β beamwidth
Figure 2 — Illustration comparing threshold and peak value detection techniques
5.6.3 Multiple-transducer systems
A variety of multiple-transducer channel sweep systems have been used since the mid-1970s. These systems
are designed to provide a broad area of coverage, rather than a single line, for each pass of the vessel. Channel
sweep systems are
...
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