IEC 63305:2024

IEC 63305 ®
Edition 1.0 2024-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Underwater acoustics – Calibration of acoustic wave vector receivers in the
frequency range 5 Hz to 10 kHz

Acoustique sous-marine – Étalonnage des récepteurs vectoriels d’ondes
acoustiques dans la plage de fréquences de 5 Hz à 10 kHz

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IEC 63305 ®
Edition 1.0 2024-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Underwater acoustics – Calibration of acoustic wave vector receivers in the

frequency range 5 Hz to 10 kHz

Acoustique sous-marine – Étalonnage des récepteurs vectoriels d’ondes

acoustiques dans la plage de fréquences de 5 Hz à 10 kHz

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50  ISBN 978-2-8322-8123-9

– 2 – IEC 63305:2024 © IEC 2024
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
4 List of symbols . 14
5 Relationship of vector quantities in sound field . 16
6 General procedures for calibration . 17
6.1 General calibration requirements . 17
6.1.1 Types of calibration . 17
6.1.2 Acoustic field requirements . 17
6.2 Acoustic standing wave tube requirements . 18
6.2.1 Requirements for standing wave tube [8] . 18
6.2.2 Requirements for immersed depth of transducers . 19
6.3 Acoustic travelling wave tube requirements . 20
6.3.1 Requirements for driving signal . 20
6.3.2 Requirements for the travelling wave tube . 20
6.4 Equipment requirements . 20
6.4.1 Calibration facility . 20
6.4.2 Instrumentation . 21
6.5 Positioning and alignment . 23
6.5.1 Coordinate system . 23
6.5.2 Reference direction . 23
6.5.3 Transducer mounting and support . 23
6.5.4 Alignment . 24
6.6 Representation of the frequency response . 25
6.7 Frequency limitations . 25
6.7.1 High-frequency limit . 25
6.7.2 Low frequency limit . 25
6.8 Checks for acoustic interference . 26
7 Electrical measurements. 26
7.1 Signal type . 26
7.2 Electrical earthing . 26
7.3 Measurement of transducer output voltage. 26
7.3.1 General . 26
7.3.2 Signal analysis . 27
7.3.3 Electrical loading by measuring instrument . 27
7.3.4 Electrical loading by extension cables . 27
7.3.5 Electrical noise . 27
7.3.6 Cross-talk . 28
7.3.7 Integral preamplifiers . 28
7.4 Measurement of projector drive current . 28
7.4.1 Instrumentation . 28
7.4.2 Signal analysis . 28
8 Preparation of measurement . 28
8.1 Preparation of transducers . 28

8.1.1 Soaking . 28
8.1.2 Wetting . 29
8.2 Environmental conditions (temperature and depth) . 29
9 Free-field calibration . 29
9.1 Free-field reciprocity calibration . 29
9.1.1 General . 29
9.1.2 Principle . 30
9.1.3 Measurement . 32
9.1.4 Uncertainty . 32
9.2 Free-field calibration using optical interferometry . 32
9.2.1 General . 32
9.2.2 Principle . 32
9.2.3 Measurement . 33
9.2.4 Uncertainty . 34
9.3 Free-field calibration using a reference hydrophone . 34
9.3.1 General . 34
9.3.2 Principle . 34
9.3.3 Measurement . 35
9.3.4 Uncertainty . 35
10 Calibration in standing wave tube . 35
10.1 Calibration using reference accelerometer . 35
10.1.1 General . 35
10.1.2 Principle . 35
10.1.3 Measurement . 37
10.1.4 Uncertainty . 37
10.2 Comparison calibration using reference hydrophone in standing wave tube . 37
10.2.1 General . 37
10.2.2 Principle . 37
10.2.3 Measurement . 39
10.2.4 Uncertainty . 39
10.3 Horizontal standing wave tube calibration . 39
10.3.1 General . 39
10.3.2 Principle . 39
10.3.3 Measurement . 41
10.3.4 Uncertainty . 41
10.4 Calibration using optical interferometry in standing wave tube . 41
10.4.1 General . 41
10.4.2 Principle . 41
10.4.3 Measurement . 43
10.4.4 Uncertainty . 43
11 Calibration in a travelling wave tube . 43
11.1 General . 43
11.2 Principle . 44
11.2.1 General . 44
11.2.2 Establishment of a unidirectional, plane progressive wave field . 45
11.2.3 Sensitivity calculations . 48
11.2.4 Uncertainty . 48
12 Reporting of results . 48

– 4 – IEC 63305:2024 © IEC 2024
12.1 Sensitivity . 48
12.2 Sensitivity level . 49
12.3 Environmental considerations for calibration . 49
12.4 Calibration uncertainties . 49
12.5 Auxiliary metadata . 49
13 Recalibration periods . 50
Annex A (informative) Directional response of a vector receiver . 51
A.1 General principle . 51
A.2 Types of measurement implementation . 51
A.3 Coordinate system . 51
A.4 Measurement of vector receiver directional response . 51
A.5 Calculation of angular deviation loss . 52
A.6 Uncertainty . 52
Annex B (informative) Inertial vector receiver calibration using optical interferometry in
air . 53
B.1 General . 53
B.2 Principle . 53
B.3 Procedure . 53
B.4 Discussion . 55
Annex C (informative) Assessment of uncertainty of vector receiver calibration . 56
C.1 General . 56
C.2 Type A evaluation of uncertainty . 56
C.3 Type B evaluation of uncertainty . 56
C.4 Reported uncertainty . 56
C.5 Common sources of uncertainty . 57
Bibliography . 60

Figure 1 – The structure of the calibration chamber . 19
Figure 2 – Co-vibrating vector receiver suspended on a mounting ring . 24
Figure 3 – Measurement framework for free-field reciprocity calibration of the vector
receiver . 30
Figure 4 – Schematic diagram of free-field calibration for vector receiver using an
optical interferometer . 33
Figure 5 – Schematic diagram of free-field comparison calibration for vector receiver
using reference hydrophone . 34
Figure 6 – Schematic diagram of vertical standing wave tube calibration using
reference accelerometer . 36
Figure 7 – Schematic diagram of vertical standing wave tube calibration using
reference hydrophone . 38
Figure 8 – Schematic diagram of calibration principle and horizontal standing wave
tube calibration . 40
Figure 9 – Schematic diagram of calibration for vector receiver using optical
interferometer in standing wave tube . 42
Figure 10 – Schematic diagram of calibration for vector receiver in a
travelling wave tube . 44
Figure B.1 – Schematic diagram of calibration using optical interferometer in air for
inertial vector receiver . 54

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
UNDERWATER ACOUSTICS – CALIBRATION OF ACOUSTIC WAVE
VECTOR RECEIVERS IN THE FREQUENCY RANGE 5 Hz TO 10 kHz

FOREWORD
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IEC 63305 has been prepared by IEC technical committee 87: Ultrasonics. It is an International
Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
87/839/FDIS 87/843/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.

– 6 – IEC 63305:2024 © IEC 2024
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
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at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
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NOTE Words in bold in the text are defined in Clause 3.
The committee has decided that the contents of this document will remain unchanged until the
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specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
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INTRODUCTION
Unlike traditional piezoelectric hydrophones which are sensitive to sound pressure, vector
receivers measure sound particle motion (velocity, acceleration or displacement) or sound
pressure gradient, and have strongly directional response in their working frequency range.
The calibration of these vector receivers which measure sound particle motion or sound
pressure gradient is considered in this document.
The output voltage of a vector receiver channel to be calibrated is proportional to the sound
particle motion or sound pressure gradient at the reference centre of the receiver. The
directivity of the vector receiver channel is independent of acoustical frequency, and the ratio
of the output voltage of the receiver channel at angle θ to the maximum output voltage on the
axial direction is equal to cosθ [1] .
Recent developments of acoustic wave vector receivers for ocean acoustics, such as those
that measure sound particle velocity, have led to a number of commercial systems being
made available on the market. In addition to providing sensors which possess some useful
directivity for low-frequency applications, they are increasingly used for measurement of
underwater noise exposure for marine fauna that are sensitive to sound particle motion rather
than sound pressure (for example, fish and invertebrates). However, calibration of such sensors
poses technical challenges, and is not covered by the existing international standards such as
IEC 60565 [2], [3]. Building on work begun in China and Russia [4], where a successful bilateral
comparison has recently been concluded, this work establishes an International Standard on
calibration of vector receivers in the frequency range 5 Hz to 10 kHz.

___________
Numbers in square brackets refer to the Bibliography.

– 8 – IEC 63305:2024 © IEC 2024
UNDERWATER ACOUSTICS – CALIBRATION OF ACOUSTIC WAVE
VECTOR RECEIVERS IN THE FREQUENCY RANGE 5 Hz TO 10 kHz

1 Scope
Usually, acoustic wave vector receivers are designed and constructed based on one of two
principles. One is the sound pressure difference (gradient) principle. When measuring with this
sensor, the vector receiver is rigidly fixed on a mount and supported in water. The other is the
co-vibrating (inertial) principle. When measuring with this sensor, the vector receiver is
suspended on a mount and supported in water in a non-rigid manner, which allows the vector
receiver co-vibrate in the same direction as the sound particle in the sound wave field.
Many methods have been used to calibrate vector receivers, such as free-field calibration,
calibration in standing wave tube and calibration in a travelling wave tube. This document
specifies methods and procedures for calibration of vector receivers in the frequency range
5 Hz to 10 kHz, which are applicable to vector receivers based on the two different principles.
In addition, it describes an absolute method of inertial vector receiver calibration in air using
optical interferometry.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
IEC 60500:2017, Underwater acoustics – Hydrophones – Properties of hydrophones in the
frequency range 1 Hz to 500 kHz
IEC 60565-1:2020, Underwater acoustics – Hydrophones – Calibration of hydrophones, Part 1:
Procedures for free-field calibration of hydrophones
ISO 80000-8:2020, Quantities and units – Part 8: Acoustics
ISO 18405:2017, Underwater acoustics – Terminology
ISO/IEC Guide 98-3, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60500:2017,
IEC 60565-1:2020, ISO 80000-8:2020, ISO 18405:2017 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp

3.1
sound particle
material element
smallest element of the medium that represents the medium’s mean density
[SOURCE: ISO 80000-8:2020, 3.1]
3.2
sound particle displacement
δ
displacement of a sound particle caused by the action of sound
Note 1 to entry: Sound particle displacement is a function of time, t, which is indicated by means of an argument
t, as in δ(t).
Note 2 to entry: Sound particle displacement is expressed in metres, m.
Note 3 to entry: Sound particle displacement is a vector quantity. Spatial components of the sound particle
displacement can be indicated by assigning subscripts to the symbol. For example, in Cartesian coordinates,
δ = (δ ,δ ,δ ). By convention in underwater acoustics, the z axis is usually chosen to point vertically down from the
x y z
sea surface, with x and y axes in the horizontal plane. If the sound particle displacement is in the same direction
in which the sound wave propagates, its symbol can be simply δ.
[SOURCE: ISO 18405:2017, 3.1.2.9, modified – In the definition, "material element" has been
replaced by "sound particle".]
3.3
sound particle velocity
u
contribution to velocity of a sound particle caused by the action of sound
Note 1 to entry: Sound particle velocity is a function of time, t, which is indicated by means of an argument t, as
in u(t).
Note 2 to entry: For small-amplitude sound waves in an otherwise stationary medium, the sound particle velocity
and sound particle displacement are related by
∂δ()t
u()t =
(1)
∂t
where δ(t) is the sound particle displacement at time, t, and the partial derivative is evaluated at a fixed position.
−1
Note 3 to entry: Sound particle velocity is expressed in units of metre per second, m·s .
Note 4 to entry: Sound particle velocity is a vector quantity. Spatial components of the sound particle velocity
can be indicated by assigning subscripts to the symbol. For example, in Cartesian coordinates, u = (u ,u ,u ). By
x y z
convention in underwater acoustics, the z axis is usually chosen to point vertically down from the sea surface, with x
and y axes in the horizontal plane. If the sound particle velocity is in the same direction in which the sound wave
propagates, its symbol can be simply u.
[SOURCE: ISO 18405:2017, 3.1.2.10, modified – In the definition, "material element" has been
replaced by "sound particle".]
3.4
sound particle acceleration
a
contribution to acceleration of a sound particle caused by the action of sound
Note 1 to entry: Sound particle acceleration is a function of time, t, which is indicated by means of an argument
t, as in a(t).
– 10 – IEC 63305:2024 © IEC 2024
Note 2 to entry: For small-amplitude sound waves in an otherwise stationary medium, the sound particle
acceleration and sound particle velocity are related by
∂u()t
a()t =
(2)
∂t
where u(t) is the sound particle velocity at time, t, and the partial derivative is evaluated at a fixed position.
−2
Note 3 to entry: Sound particle acceleration is expressed in units of metre per second squared, m·s .
Note 4 to entry: Sound particle acceleration is a vector quantity. Spatial components of the sound particle
acceleration can be indicated by assigning subscripts to the symbol. For example, in Cartesian coordinates,
a = (a ,a ,a ). By convention in underwater acoustics, the z axis is usually chosen to point vertically down from the
x y z
sea surface, with x and y axes in the horizontal plane. If the sound particle acceleration is in the same direction in
which the sound wave propagates, its symbol can be simply a.
[SOURCE: ISO 18405:2017, 3.1.2.11, modified – In the definition, "material element" has been
replaced by "sound particle".]
3.5
sound pressure gradient
∇p
spatial derivative of sound pressure with respect to distance caused by the action of sound
−1
Note 1 to entry: Sound pressure gradient is expressed in units of pascal per metre, Pa·m .
Note 2 to entry: Sound pressure gradient is a vector quantity. In Cartesian coordinates, spatial components of the
sound pressure gradient can be indicated as ∇p=(∂∂p / x,∂∂p / y,∂p /∂z) . By convention in underwater acoustics, the
z axis is usually chosen to point vertically down from the sea surface, with x and y axes in the horizontal plane.
3.6
vector receiver
acoustic wave vector receiver
receiving transducer whose output voltage of its receiving channel is proportional to the sound
particle motion (displacement, velocity or acceleration) or sound pressure gradient on the
position of the reference centre of it in water
Note 1 to entry: Due to the different constructions, the vector receiver can be one-dimensional vector receiver,
two-dimensional orthogonal vector receiver or three-dimensional orthogonal vector receiver, and it has different
receiving channels. For a three-dimensional orthogonal vector receiver, the channels are usually named as
x-channel, y-channel and z-channel.
Note 2 to entry: The receiving channel of the vector receiver has very strong directional response, which is
independent of the frequency.
Note 3 to entry: According to the vector values which are perceived, there are different vector receivers, including
inertial vector receiver and sound pressure gradient receiver.
Note 4 to entry: Sometimes, the vector receiver has a sound pressure (scalar) receiving channel, and open-circuit
voltage of the sound pressure channel is proportional to the sound pressure on the position of the reference centre
of the vector receiver.
Note 5 to entry: The phase of the output signal of the vector receiving channel changes by 180 degrees when the
direction of sound wave incidence changes to the opposite direction, which can be found using the output signal of
a sound pressure receiving channel as a reference signal when the vector receiver has a sound pressure receiving
channel in it.
3.7
inertial vector receiver
receiving transducer that senses sound particle motion by measuring the reaction of a proof
mass in response to motion of the sensor body (e.g. accelerometer, geophone)

3.8
hydrophone
electroacoustic transducer that produces electrical voltages in response to water borne sound
pressure signals
[SOURCE: IEC 60500:2017, 3.17, modified – In the definition, "electrical signals" has been
replaced with "electrical voltages", and "pressure signals" with "sound pressure signals".]
3.9
sound pressure gradient receiver
receiving transducer that senses the gradient of sound pressure using two or more
hydrophones separated by distances that are small relative to the wavelength
3.10
directional response
description of the response of a vector receiver channel, as a
function of the direction of propagation of the incident plane sound wave, in a given channel
direction through the reference centre, at a specified frequency
Note 1 to entry: The directional response pattern is usually presented in the form of a two-dimensional polar
graph. The scale of the polar can be in terms of sensitivity level or in angular deviation loss (see Annex A).
Note 2 to entry: The directional response pattern of the vector receiver channel is a cosine function, that is the
ratio of the output voltage of the vector receiver channel in the direction of angle θ to the maximum output voltage
in the axial direction is equal to .
cosθ
[SOURCE: IEC 60500:2017, 3.4, modified – In the definition, "hydrophone" has been replaced
with "vector receiver channel", "a specified plane" has been replaced with "a given channel
direction", and ", generally presented graphically," has been deleted.]
3.11
axial angular deviation loss
larger value of directional response of a vector receiver channel on the principal axis minus
another value of directional response on the symmetrical direction
Note 1 to entry: The axial angular deviation loss is expressed as a level in decibels, dB (see Annex A).
Note 2 to entry: Sometimes, the axial angular deviation loss is named as asymmetry or maximum heterogeneity
of directional response on the principal axis of a vector receiver channel.
3.12
lateral angular deviation loss
larger value of directional response of a vector receiver channel on the principal axis minus
the smaller value of directional response on the lateral axis
Note 1 to entry: The lateral angular deviation loss is expressed as a level in decibels, dB (see Annex A).
3.13
sound particle displacement sensitivity
M
δ
quotient of the Fourier transform of the output voltage signal
of a vector receiver channel to the Fourier transform of the sound particle
 Ut
( ())
VR
displacement signal  δ t , for specified frequency and specified direction of plane wave
( ())
sound incidence on the position of the reference centre of the vector receiver in the
undisturbed free field if the vector receiver was removed

– 12 – IEC 63305:2024 © IEC 2024
 Ut
( ())
VR
M =
(3)
δ
 δ t
( ())
Note 1 to entry: The sound particle displacement sensitivity of a vector receiver is a complex-valued parameter.
The sound particle displacement sensitivity calculated by this equation is in the direction of the sound wave
propagation. This calibration procedure can be performed for only one aligned channel, and each channel of the
vector receiver is calibrated independently.
Note 2 to entry: The modulus of the sound particle displacement sensitivity is expressed in units of volt per
−1
metre, V·m .
Note 3 to entry: The phase angle of the sound particle displacement sensitivity is expressed in radians and
represents the phase difference between the output voltage of a vector receiver and the sound particle
displacement (see IEC 60500).
3.14
sound particle displacement sensitivity level
L
M,δ
twenty times the logarithm to the base 10 of the ratio of the modulus of the sound particle
displacement sensitivity M of a vector receiver channel to a reference value of
δ
sensitivity, M , in decibels
δ,ref
M
δ
L = 20log dB
(4)
M,δ 10
M
δ,ref
Note 1 to entry: The unit of sound particle displacement sensitivity level is expressed as a level in decibels, dB.
−1
Note 2 to entry: The reference value of sensitivity, M , is 1 V·pm .
δ,ref
3.15
sound particle velocity sensitivity
M
u
quotient of the Fourier transform of the output voltage signal
of a vector receiver channel to the Fourier transform of the sound particle
 Ut()
( )
VR
velocity signal  ut , for specified frequency and specified direction of plane wave sound
( ())
incidence on the position of the reference centre of the vector receiver in the undisturbed free
field if the vector receiver was removed
 Ut
( ())
VR
M =
(5)
u
 ut()
( )
Note 1 to entry: The sound particle velocity sensitivity of vector receivers is a complex-valued parameter. The
sound particle velocity sensitivity calculated by this equation is in the direction of the sound wave propagation.
This calibration procedure can be performed for only one aligned channel, and each channel of the vector receiver
is calibrated independently.
Note 2 to entry: The modulus of the sound particle velocity sensitivity is expressed in units of volt second per
−1
metre, V·s·m .
Note 3 to entry: The phase angle of the sound particle velocity sensitivity is expressed in radians and represents
the phase difference between the output voltage of a vector receiver and the sound particle velocity
(see IEC 60500).
3.16
sound particle velocity sensitivity level
L
M,u
twenty times the logarithm to the base 10 of the ratio of the modulus of the sound particle
M
velocity sensitivity
...