IEC 60565-1 Ed. 1.0 b:2020

Underwater acoustics - Hydrophones - Calibration of hydrophones

Part 1: Procedures for free-field calibration of hydrophones

IEC 60565-1:2020 specifies methods and procedures for free-field calibration of hydrophones, as well as individual electroacoustic transducers that can be used as hydrophones (receivers) and/or projectors (source transducers). Two general types of calibration are covered within this document: absolute calibration using the method of three-transducer spherical-wave reciprocity, and relative calibration by comparison with a reference device which has already been the subject of an absolute calibration.

The maximum frequency range of the methods specified in this document is from 200 Hz to 1 MHz. The lowest acoustic frequency of application will depend on a number of factors, and will typically be in the range 200 Hz to 5 kHz depending mainly on the dimensions of the chosen test facility. The highest frequency of application for the methods described here is 1 MHz.

Procedures for pressure hydrophone calibration at low frequencies can be found in IEC 60565-2 [1]. Procedures for hydrophone calibration at acoustic frequencies greater than 1 MHz are covered by IEC 62127-2 [2].

Excluded from the scope of this document are low-frequency pressure calibrations of hydrophones, which are described in IEC 60565-2 [1]. Also excluded are calibrations of:

• digital hydrophones and systems,
• marine autonomous acoustic recorders,
• acoustic vector sensors such as particle velocity sensors and pressure gradient hydrophones,
• passive sonar arrays consisting of multiple hydrophones, and
• active sonar arrays consisting of projectors and hydrophones.

This document presents a description of the requirements for free-field calibration in terms of test facility, equipment and instrumentation, signal processing, and frequency limitations. A description of achievable uncertainty and rules for the presentation of the calibration data are provided.

Also included are informative annexes that provide additional guidance on:

• measurement of directional response of a hydrophone or projector,
• measurement of electrical impedance of hydrophones and projectors,
• electrical loading corrections,
• acoustic far-field criteria in underwater acoustic calibration,
• pulsed techniques in free-field calibrations,
• assessment of uncertainty in the free-field calibration of hydrophones and projectors,
• derivation of the formulae for three-transducer spherical-wave reciprocity calibrations,
• calibration using travelling-wave tubes,
• calibration of hydrophones using optical interferometry, and
• calibrations in reverberant water tanks using continuous signals.

IEC 60565-1:2020 together with IEC 60565-2:2019, cancels and replaces the second edition of IEC 60565 published in 2006. This edition constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous edition:

• Removal of all descriptions of methods for pressure calibrations of hydrophones – these are now included in Part 2;
• Removal of the derivations of formulae for free-field reciprocity calibration (both amplitude sensitivity and phase sensitivity) and placement of these into an informative annex;
• Inclusion within the scope of the calibration of the transmitting response of individual source transducers and hydrophones (but not sonar arrays);
• Re-ordering of the sections within the document such that the more general procedures for calibration such as guidance on obtaining conditions of acoustic free-field, far-field, and steady-state, appear before the descriptions of procedures for absolute or relative calibrations;
• Revision of informative Annex A to include guidance on measurement of directional response of a hydrophone or projector;
• Addition of a new informative Annex B on measurement of electrical impedance of hydrophones and projectors;
• Revision of the previous informative annex on electrical loading corrections to include corrections to account for electrical loading by added cables (now Annex C);
• Addition of a new informative Annex D on acoustic far-field criteria in underwater acoustic calibration;
• Revision of the previous informative annex on pulsed techniques in free-field calibrations (now Annex E);
• Revision of the previous informative annex on assessment of uncertainty in the calibration of hydrophones (now Annex F);
• Deletion of the previous informative annex on equivalent circuit of the excitation system for calibration with a vibrating column;
• Addition of a new informative Annex G on derivation of the formulae for three-transducer spherical-wave reciprocity calibration;
• Addition of a new informative Annex H on calibration using travelling-wave tubes;
• Addition of a new informative Annex I on calibration of hydrophones using optical interferometry;
• Addition of a new informative Annex J on calibration in reverberant water tanks using continuous signals.