New measurement capabilities to protect the marine environment

Underwater noise from man-made activity, such as shipping or construction work, can have a profound effect on marine organisms such as whales, damaging their hearing or driving them from their native habitats. European directives are in place to protect the most vulnerable species, but no validated calibration methods were available for underwater measurement instruments in the sound range of greatest environmental concern.


The EU Marine Strategy Framework Directive (MSFD) aims to
protect vulnerable marine ecosystems by limiting underwater
noise from man-made activity, such as shipping or construction
work, which can adversely affect marine wildlife. The sources
of greatest environmental concern radiate most of their sound
energy in the low frequency range 20 Hz to 1 kHz. However, the
response of hydrophones, that are used to detect underwater
noise, are relatively flat at these frequencies and require accurate
calibrations for which no traceable methodologies existed in
In addition, no measurement standards existed for new, emerging
technologies such as autonomous noise recorders that combine
hydrophones with data acquisition and storage capabilities.
These present particular challenges regarding low frequency
calibration given the wide variety of acoustic sensors they
can employ. If the hydrophone and recorder are calibrated as
one system, then sound waves interacting with the body may
influence the measurement result and if calibrated separately then
the measurement results require combining to form the overall
system sensitivity. Thus, new metrology was required to ensure
compliance to the MSFD. Furthermore, as underwater acoustics is
a relatively immature field, metrology strategies were required to
develop long-term capabilities in Europe within this area.


TÜBİTAK’s Marmara Research Center Materials Institute Underwater
Acoustic Laboratory (MRC MI-UAL) coordinated the EMPIR project
Underwater acoustic calibration standards for frequencies below
1 kHz which sought to address the measurement challenges
posed by low frequency measurements. During the project MRC
MI-UAL developed a calibration method for hydrophones at
frequencies from 20 Hz to 2 kHz using a novel pressure coupling
chamber method. A similar methodology was used by MRC MIUAL
and project partner NPL to establish calibration methods for
autonomous noise recorders over the range 20 Hz to 1 kHz. Project
partners FOI, CNR and ISPRA also developed free field calibration
setups and procedures for autonomous recorders and all methods
were then validated through a series of inter-comparisons. MRC
MI-UAL now offers new calibration services for hydrophones
and noise recorders in the frequency range from 20 Hz to 1 kHz,
including the 63 Hz and 125 Hz third-octave low frequency bands
specifically required by the MSFD.


RTsys, founded in 2010, is a R&D orientated company specializing
in the design and manufacturing of advanced underwater
acoustics systems. As well as manufacturing autonomous
underwater vehicles and sonar for divers the company also
produces acoustic recorders for scientific customers and people
working on marine subjects – especially those around the MSFD.
MRC MI-UAL calibrated the company’s RESEA autonomous
recorders before use in a six-month noise monitoring programme
during construction of the 1915 bridge across the Dardanelle
straits. With input from MRC MI-UAL the construction company
was able to minimize disruption to marine life by avoiding
certain sea regions, arranging the frequency and timing of their
work and generating higher frequencies during piling. RTsys
can now perform acoustic measurements at low frequencies
and provide more accurate calibration results and values to their customers, allowing them to use the RESEA recorders in a
more efficient way and improving the accuracy and relevance
of their post data collection processing. Individual strategies
for long-term measurement capabilities and new or extended
calibration services are now available in Europe for hydrophones
and noise recorders in the low frequency range 20 Hz to 1 kHz.
This will enable industry and manufactures of recorder systems
to demonstrate compliance to EU directives helping to protect
vulnerable marine species.

  • Category
  • EMPIR,
  • Environment,
Element 1 Element 2 Element 3 Element 1 Element 1 Element 1 Element 1 Element 1 Logo-Footer