SIST EN 60500:2017
(Main)Underwater acoustics - Hydrophones - Properties of hydrophones in the frequency range 1 Hz to 500 kHz (IEC 60500:2017)
Underwater acoustics - Hydrophones - Properties of hydrophones in the frequency range 1 Hz to 500 kHz (IEC 60500:2017)
This document specifies the relevant characteristics and properties of hydrophones in the
frequency range 1 Hz to 500 kHz, and specifies how to report these characteristics. It does
not cover performance requirements for specific hydrophone types, or for specific hydrophone
applications. However, guidance on the choice of a hydrophone with appropriate performance
for a specific application is given in an informative annex.
This document is applicable to:
• hydrophones employing piezoelectric sensor elements, designed to respond to sound
pressure in water and measure underwater acoustical signals;
• hydrophones with or without an integral pre-amplifier.
Unterwasserakustik - Hydrophone - Eigenschaften von Hydrophonen im Frequenzbereich von 1 Hz bis 500 kHz
Acoustique sous-marine - Hydrophones - Propriétés des hydrophones dans la bande de fréquences de 1 Hz à 500 kHz
L'IEC 60500:2017 spécifie les caractéristiques et les propriétés pertinentes des hydrophones dans la bande de fréquences de 1 Hz à 500 kHz, ainsi que la manière de déclarer ces caractéristiques. Cette norme donne des lignes directrices relatives au choix d’un hydrophone présentant des performances appropriées pour une application spécifique. Le présent document est applicable aux:
- hydrophones employant des éléments sensibles piézoélectriques conçus pour répondre à la pression acoustique dans l’eau et mesurer les signaux acoustiques sous-marins;
- hydrophones avec ou sans préamplificateur intégré.
Cette nouvelle édition inclut les modifications techniques majeures suivantes par rapport à l’édition précédente:
- le format et le domaine d’application de l’IEC 60500 ont été modifiés de manière à les rendre compatibles avec d'autres normes IEC;
- la limite supérieure de la bande de fréquences des hydrophones a été étendue.
Podvodna akustika - Hidrofoni - Lastnosti hidrofonov v frekvenčnem območju od 1 Hz do 500 kHz (IEC 60500:2017)
Ta dokument določa ustrezne značilnosti in lastnosti hidrofonov v frekvenčnem območju od 1 Hz do 500 kHz in določa, kako poročati o teh značilnostih. Ne zajema zahtev glede zmogljivosti za določene vrste hidrofonov ali za njihovo specifično uporabo. Kljub temu so v informativnem dodatku opredeljene smernice za izbiro hidrofona z ustrezno zmogljivostjo za določeno uporabo.
Ta dokument se uporablja za:
• hidrofone s piezoelektričnimi senzornimi elementi, ki so zasnovani tako, da reagirajo na zvočni tlak v vodi in merijo podvodne zvočne signale;
• hidrofone z vgrajenim predojačevalnikom ali brez njega.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 60500:2017
01-oktober-2017
3RGYRGQDDNXVWLND+LGURIRQL/DVWQRVWLKLGURIRQRYYIUHNYHQþQHPREPRþMXRG
+]GRN+] ,(&
Underwater acoustics - Hydrophones - Properties of hydrophones in the frequency range
1 Hz to 500 kHz (IEC 60500:2017)
Ta slovenski standard je istoveten z: EN 60500:2017
ICS:
17.140.99 Drugi standardi v zvezi z Other standards related to
akustiko acoustics
SIST EN 60500:2017 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 60500:2017
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SIST EN 60500:2017
EUROPEAN STANDARD EN 60500
NORME EUROPÉENNE
EUROPÄISCHE NORM
July 2017
ICS 17.140.50
English Version
Underwater acoustics - Hydrophones -
Properties of hydrophones in the frequency range
1 Hz to 500 kHz
(IEC 60500:2017)
Acoustique sous-marine - Hydrophones - Unterwasserakustik - Hydrophone -
Propriétés des hydrophones dans la bande de fréquences Eigenschaften von Hydrophonen im Frequenzbereich
de 1 Hz à 500 kHz von 1 Hz bis 500 kHz
(IEC 60500:2017) (IEC 60500:2017)
This European Standard was approved by CENELEC on 2017-05-15. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,
Switzerland, Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 60500:2017 E
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SIST EN 60500:2017
EN 60500:2017
European foreword
The text of document 87/644/FDIS, future edition 2 of IEC 60500, prepared by IEC/TC 87 "Ultrasonics"
was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as EN 60500:2017.
The following dates are fixed:
• latest date by which the document has to be implemented at (dop) 2018-02-15
national level by publication of an identical national
standard or by endorsement
• latest date by which the national standards conflicting with (dow) 2020-05-15
the document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Endorsement notice
The text of the International Standard IEC 60500:2017 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 60565:2006 NOTE Harmonized as EN 60565:2007 (not modified).
IEC 62127-3:2007 NOTE Harmonized as EN 62127-3:2007 (not modified)
+ A1:2013 + A1:2013 (not modified).
2
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SIST EN 60500:2017
EN 60500:2017
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is
available here: www.cenelec.eu.
Publication Year Title EN/HD Year
ISO 266 1997 Acoustics - Preferred frequencies EN ISO 266 1997
3
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SIST EN 60500:2017
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SIST EN 60500:2017
IEC 60500
®
Edition 2.0 2017-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Underwater acoustics – Hydrophones – Properties of hydrophones in the
frequency range 1 Hz to 500 kHz
Acoustique sous-marine – Hydrophones – Propriétés des hydrophones dans la
bande de fréquences de 1 Hz à 500 kHz
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.140.50 ISBN 978-2-8322-4049-6
Warning! Make sure that you obtained this publication from an authorized distributor.
Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
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SIST EN 60500:2017
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CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Symbols . 11
5 Hydrophone characteristics . 12
5.1 General . 12
5.2 Basic requirements . 12
5.3 Sensitivity . 12
5.4 Frequency response . 13
5.4.1 Stated operating frequency band . 13
5.4.2 Frequency dependence . 13
5.5 Directional response . 13
5.6 Dynamic range . 13
5.6.1 Linearity and overload sound pressure level . 13
5.6.2 Equivalent noise pressure spectral density level . 14
5.6.3 Conditions required . 14
5.7 Electrical requirements . 14
5.7.1 Electromagnetic interference . 14
5.7.2 Electrical characteristics . 14
5.8 Mechanical requirements . 14
5.9 Environmental aspects . 15
5.10 Stability of the sensitivity . 15
5.10.1 Temperature stability . 15
5.10.2 Depth stability . 15
5.10.3 Time stability . 15
6 Information to be supplied by the manufacturer . 16
Annex A (informative) Recommendations for selecting hydrophones . 18
A.1 General . 18
A.2 Sensitivity . 18
A.3 Self–noise performance . 19
A.4 Frequency response . 19
A.5 Directional response . 20
A.6 Dynamic range . 20
A.7 Electrical connection . 21
A.8 Stability of the sensitivity . 21
A.8.1 Temperature stability . 21
A.8.2 Depth stability . 21
A.8.3 Time stability . 21
Bibliography . 22
Figure 1 – Angular co-ordinate system . 6
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SIST EN 60500:2017
IEC 60500:2017 © IEC 2017 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
UNDERWATER ACOUSTICS – HYDROPHONES – PROPERTIES OF
HYDROPHONES IN THE FREQUENCY RANGE 1 Hz TO 500 kHz
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60500 has been prepared by IEC technical committee 87:
Ultrasonics.
This second edition cancels and replaces the first edition published in 1974. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition.
a) The format and scope of IEC 60500 have been changed to be compatible with
IEC 62127-3:2007 in accordance with ISO/IEC Directives, and has a good conformity with
IEC 60565:2006, making the suite of available standards for underwater sound a more
coordinated and coherent system.
b) The upper limit of the frequency range of hydrophones has been expanded from 100 kHz
to 500 kHz.
c) Technical requirements of hydrophone selecting are provided in Annex A, and the depth
range of the static pressure range of hydrophones has been expanded from 10 m to 100 m.
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The text of this International Standard is based on the following documents:
FDIS Report on voting
87/644/FDIS 87/649/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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SIST EN 60500:2017
IEC 60500:2017 © IEC 2017 – 5 –
UNDERWATER ACOUSTICS – HYDROPHONES – PROPERTIES OF
HYDROPHONES IN THE FREQUENCY RANGE 1 Hz TO 500 kHz
1 Scope
This document specifies the relevant characteristics and properties of hydrophones in the
frequency range 1 Hz to 500 kHz, and specifies how to report these characteristics. It does
not cover performance requirements for specific hydrophone types, or for specific hydrophone
applications. However, guidance on the choice of a hydrophone with appropriate performance
for a specific application is given in an informative annex.
This document is applicable to:
• hydrophones employing piezoelectric sensor elements, designed to respond to sound
pressure in water and measure underwater acoustical signals;
• hydrophones with or without an integral pre-amplifier.
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.
ISO 266:1997, Acoustics – Preferred frequencies
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
angular co-ordinate system
system used to designate the directional response pattern of the hydrophone
Note 1 to entry: The terms “horizontal directional response” and “vertical directional response” are often used for
representation of directional response in the xy-plane, and xz- (or yz-) planes respectively.
Note 2 to entry: “+z” is coincident with an axis of the hydrophone, and “−z” is in the direction of the hydrophone
cable.
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z
θ
r
y
φ
x
IEC
Key
r radial distance
θ polar angle
ϕ azimuthal angle
Figure 1 – Angular co-ordinate system
3.2
end-of-cable capacitance
C
H
electrical capacitance measured at the end of the integral cable of a
hydrophone at a frequency well below any pronounced resonance
Note 1 to entry: End-of-cable capacitance is expressed in farad, F.
Note 2 to entry: The frequency is stated along with the value of end-of-cable capacitance. The end-of cable
capacitance is typically measured at a frequency of 1 kHz.
3.3
diffraction factor
ratio of the root-mean-square sound pressure averaged over the part of the hydrophone
designed to receive an incident plane wave sound pressure from a given direction to the free-
field root-mean-square sound pressure that would exist at the reference centre of the
hydrophone if the hydrophone was removed
1
[SOURCE: IEC 60565:2006 [1] , 3.4, modified – Replace “averaged pressure” with “root-
mean-square sound pressure averaged”, “receive sound” with “receive an incident plane wave
sound pressure from a given direction”, “free-field sound pressure” with “free-field root-mean-
square sound pressure”, and add “if the hydrophone was removed”.]
3.4
directional response
description, generally presented graphically, of the response of a
hydrophone, as a function of the direction of propagation of the incident plane sound wave, in
a specified plane 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 may be in terms of sensitivity level or as relative values normalized to the sensitivity
in a specified direction (often the direction of the principal axis). The relative values are sometimes presented in
decibels as a relative directional response level. See Figure 1 for description of angular co-ordinate system.
___________
1
Numbers in square brackets refer to the Bibliography.
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IEC 60500:2017 © IEC 2017 – 7 –
[SOURCE: IEC 62127-3:2007 [2], 3.1, modified – Add the specific context "
hydrophone>" and Note 1 to entry.]
3.5
dynamic range
twenty times the logarithm to the base 10 of the ratio of the overload sound pressure in a
specified frequency band that produces an undistorted hydrophone output to the equivalent
bandwidth noise pressure at the hydrophone
Note 1 to entry: Dynamic range is expressed in decibel, dB.
[SOURCE: IEC 60565:2006 [1], 3.6, modified – Replace “ratio” with “twenty times the
logarithm to the base 10 of the ratio”, “maximum free-field sound pressure” with “overload
sound pressure in a specified frequency band”, and “equivalent noise pressure” with
“equivalent bandwidth noise pressure”.]
3.6
electrical impedance
Z
complex valued quantity, the modulus of which is the ratio of the root-
mean-square voltage applied across the electrical terminals of a hydrophone to the resulting
root-mean-square current, and the argument of which is the phase difference between voltage
and current, at a specified frequency
Note 1 to entry: Electrical impedance of a hydrophone is expressed in ohm, Ω.
Note 2 to entry: Because the electrical impedance depends on the hydrostatic pressure, water temperature and
the length of the cable attached to the hydrophone, these parameters, as well as the frequency and the electrical
terminals where the electrical impedance is measured, should be specified.
3.7
electrical terminals
terminals across which the open-circuit voltage of a hydrophone is
measured
3.8
end-of-cable
specification that relates to the end of the integral cable of a hydrophone with or without an
integral pre-amplifier
Note 1 to entry: If the hydrophone is not provided with an integral cable, the specification relates to the output
connector firmly connected with the hydrophone, not any additional extension cable.
[SOURCE: IEC 62127-3:2007 [2], 3.4, modified – Replace “integral output cable if the
hydrophone or hydrophone assembly is provided with such a cable; if the hydrophone or
hydrophone assembly is not provided with an integral output cable, the specification relates to
the output connector firmly connected with the hydrophone or hydrophone assembly, not to an
extra cable” with “integral cable of a hydrophone with or without an integral pre-amplifier”. Add
Note 1 to entry.]
3.9
end-of-cable leakage resistance
R
L
ratio of the root-mean-square voltage across the end-of-cable electrical terminals of a
hydrophone to the direct root-mean-square current flowing through these terminals
Note 1 to entry: End-of-cable leakage resistance is expressed in ohm, Ω.
Note 2 to entry: The value of the voltage used during the determination of the end-of-cable leakage resistance
should be stated.
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[SOURCE: IEC 60866:1987 [3], 3.13, modified – Replace “voltage across the electrical
terminals at the end of the hydrophone cable to the direct current” with “root-mean-square
voltage across the end-of-cable electrical terminals of a hydrophone to the direct root-mean-
square current”.]
3.10
equivalent bandwidth noise pressure
p
W
ratio of the root-mean-square noise voltage in the relevant frequency band present at the
electrical terminals of the hydrophone, in the absence of sound pressure or pressure
fluctuations at the hydrophone input, to its sensitivity in a specified frequency band
Note 1 to entry: Equivalent bandwidth noise pressure is expressed in pascal, Pa.
3.11
equivalent noise pressure spectral density
p
s
equivalent bandwidth noise pressure when its bandwidth is 1 Hz
Note 1 to entry: Equivalent noise pressure spectral density is expressed in pascal per square root of hertz,
-1/2
Pa ⋅ Hz .
3.12
equivalent noise pressure spectral density level
twenty times the logarithm to the base 10 of the ratio of the equivalent noise pressure spectral
density of a hydrophone, p , to a reference pressure spectral density, p
s s0
Note 1 to entry: Equivalent noise pressure spectral density level of a hydrophone is expressed in decibel, dB.
-1/2
Note 2 to entry: The value of reference pressure spectral density, p , is 1 µPa ⋅ Hz .
s0
3.13
free field
sound field in a homogeneous and isotropic medium in which the effects of the boundaries are
negligible
[SOURCE: IEC 60565:2006 [1], 3.13]
3.14
free-field open-circuit complex sensitivity
M
f
complex valued quantity, the modulus of which is the free-field open-circuit sensitivity and the
argument of which is the sensitivity phase angle, for specified frequency and specified
direction of sound incidence at the position of the reference centre of the hydrophone if the
hydrophone was removed from the sound field
3.15
free-field open-circuit sensitivity
M
f
modulus of the free-field open-circuit complex sensitivity, which is equal to the ratio of the
open-circuit root-mean-square voltage at the end-of-cable of a hydrophone to the root-mean-
square sound pressure for specified frequency and specified direction of plane wave sound
incident on the position of the reference centre of the hydrophone in the undisturbed free field
if the hydrophone was removed
Note 1 to entry: Free-field open-circuit sensitivity is expressed in volt per pascal, V/Pa.
Note 2 to entry: The term ‘response’ is sometimes used instead of ‘sensitivity’.
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IEC 60500:2017 © IEC 2017 – 9 –
3.16
free-field open-circuit sensitivity level
twenty times the logarithm to the base 10 of the ratio of the free-field open-circuit sensitivity,
M , to a reference sensitivity, M
f ref
Note 1 to entry: Free-field open-circuit sensitivity level is expressed in decibel, dB.
Note 2 to entry: The value of reference sensitivity, M , is 1 V/µPa.
ref
3.17
hydrophone
electroacoustic transducer that produces electrical signals in response to water borne
pressure signals
Note 1 to entry: A hydrophone is designed to respond principally to underwater sound pressure.
Note 2 to entry: In general, a hydrophone may also produce a signal in response to non-acoustic pressure
fluctuations (for example, those existing in a turbulent boundary layer during conditions of high water flow).
Note 3 to entry: Hydrophone types include reference hydrophones and measuring hydrophones. Measuring
hydrophones are used in general measurements of sound fields, and reference hydrophones are principally used
for calibration purposes (for example in comparison calibrations with measuring hydrophones).
Note 4 to entry: Hydrophones are principally used for listening devices, but in reciprocity calibration, a
hydrophone is used as reciprocal transducer, not only acting as a hydrophone, but also as a projector (sound
source).
Note 5 to entry: A hydrophone which is integrated with a digital acquisition system is sometimes termed a “digital
hydrophone”, but the combination is best considered as a measuring system, not a hydrophone alone.
Note 6 to entry: If a hydrophone is connected to a charge amplifier, the sensitivity of the hydrophone is
sometimes described in terms of charge sensitivity, which is related to the voltage sensitivity of the hydrophone by
its electrical capacitance.
[SOURCE: IEC 60565:2006 [1], 3.16, modified – Replace “transducer” with “electroacoustic
transducer”, and “water borne acoustic signals” with “water borne pressure signals”. Replace
the note with Notes 1 to 6 to entry.]
3.18
open-circuit voltage
U
H
voltage appearing at the electrical terminals of a hydrophone when no current passes through
the terminals
Note 1 to entry: Open-circuit voltage at hydrophone is expressed in volt, V.
[SOURCE: IEC 60565:2006 [1], 3.19, modified – Delete "at hydrophone" from the term.]
3.19
overload sound pressure
p
o
ratio of the maximum root-mean-square sound pressure applied at the hydrophone to cause a
distorted voltage output with specified criteria (linearity) to a reference sound pressure at a
specified frequency
Note 1 to entry: Overload sound pressure is expressed in pascal, Pa.
Note 2 to entry: The distortion tolerance criteria should be specified.
3.20
overload sound pressure level
twenty times the logarithm to the base 10 of the ratio of the overload sound pressure, p , to a
o
reference sound pressure, p
o0
Note 1 to entry: Overload sound pressure level is expressed in decibel, dB.
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Note 2 to entry: The value of reference sound pressure, p , is 1 µPa.
o0
3.21
phase angle
argument of the free-field open-circuit complex sensitivity, which is equal to the phase
difference between open-circuit voltage at the end-of-cable of a hydrophone and sound
pressure for specified frequency and specified direction of plane-wave sound incident on the
position of the reference centre of the hydrophone in the undisturbed free field if the
hydrophone was removed
3.22
pre-amplifier
active electronic device, often integrated into a particular hydrophone design, reducing the
hydrophone output impedance and amplifying the hydrophone output signal
Note 1 to entry: A pre-amplifier requires an electrical power supply voltage.
Note 2 to entry: The pre-amplifier may have a forward voltage transmission factor of less than one, i.e. it need not
necessarily be a volta
...
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