Time (s)

An

gle

(d

eg

ree

s)

0 10 20 30 40 50 60

-80

-60

-40

-20

0

20

40

60

80

Pump via bottom reflection

Pump via surface reflection

Pump

Drag head

Underwater Anthropogenic Noise

www.southampton.ac.uk

BackgroundThere is a growing awareness of underwater anthropogenic (man made) noise and its potential impact on marine life. The EC has recognized this by including two indicators of underwater noise in its criteria for the good environmental status of marine waters, as part of the Marine Strategy Framework Directive (MSFD).  In addition to long term monitoring there is a need to measure and monitor the noise generated by noise sources including ships, marine construction and off-shore renewables.

The University of Southampton has been involved in a project to measure the noise generated by dredging vessels during marine aggregate extraction operations. Each year these provide 20 million tonnes of sand and gravel from the seabed in UK coastal waters for use in construction industries. For aggregate extraction, a trailing suction hopper dredger is used, which lowers a drag head and suction pipe to the sea floor to extract the sand or gravel.

ResearchThe research consortium performed measurements on 6 vessels in 3 different areas around the UK’s coast, with one vessel being measured in two different areas. The radiated underwater noise was measured using hydrophones deployed from a survey vessel, autonomous recording buoys and a vertical array with electronic position sensing.

In addition to measuring the radiated noise at given distances, the use of propagation loss models allowed the source levels of each vessel to be calculated. These source levels are an essential input to numerical models for calculating noise maps and exposures.

The cooperation of the vessel masters enabled the noise generation mechanisms to be identified by operating the vessels in various modes (e.g. pumping water but not aggregate). In addition, the use of the vertical array enabled sources to be identified in elevation, in particular the noise from the mid-water pump on the suction pipe.

CollaborationThis research was performed by a consortium led by the National Physical Laboratory, with Loughborough University, the University of Southampton and Gardline Environmental Ltd. This work was funded by MALSF under project MEPF 09/P108. The support of the vessel operators is greatly appreciated.

ImpactThis work has:

o Provided a definitive set of data on the radiated noise from a representative cross-section of vessels within the U.K. marine aggregate extraction fleet.

o Provided data that will be used as the basis for making environmental impact assessments when applying for licences for new dredging areas.

o Aided the development of techniques for measuring the radiated noise level and source level that will be used in further work and that will help guide the development of measurement standards in this area. Key investigators are on the new ISO Committee on Underwater Acoustics (ISO/TC43 SC3).

Received levels from the Sand Falcon at 100 m comparing levels for full dredging (draghead

down, pump on), pumping with draghead raised from the seabed,

and with the pump switched off. Also

shown is the ambient noise level.

Identification of noise sources

using the vertical array showing

strong radiation from the mid-

water pump. The beamformer

output has been summed over all

frequencies and is plotted as a

function of time.

The Sand Falcon undertaking dredging in Area 473 in the English Channel.

Victor Humphrey, ISVR Fluid Dynamics and Acoustics Group(vh@isvr.soton.ac.uk)