in Helsinki Peter Sigray Coordinator of the BIAS-project Helsinki - - PowerPoint PPT Presentation

Peter Sigray Coordinator of the BIAS-project

HELCOM-BIAS Workshop in Helsinki

Helsinki November 2014

Underwater Acoustics and Sources

Underwater Acoustics

• Source generating sound
• A medium wherein the sound

can propagate

• A reciever that is affected

There are natural occurring sound and human-made sound

Natural biological sound

From DOSIT Discovery of the sound in the sea; http://www.dosits.org/

Natural abiotic ambient sound

From DOSIT Discovery of the sound in the sea; http://www.dosits.org/

Anthropogenic sound

From DOSIT Discovery of the sound in the sea; http://www.dosits.org/

So Sour urces ces

Summary of sources

Natural biological sound Natural non-biological sound Anthropogenic Sound

The anthropogenic sound levels are rising.

McDonald et al., 2006

Propagation of sound in water

Wave propagation depends on several factors

• Sea surface
• Sea bed
• Sound velocity
• Absorption

Sound velocity of the deep

• ceans

Underwater sound from the perspective of a fish

Sound consists of both:

• Sound pressure variations (swim bladder involved)
• Particle motion– hearing organ (otholits)
• Two main categorize of sound: Impulsive and

continuous Both co-exists!

Particle motion Pressure

http://www.acs.psu.edu/drussell /demos/waves/wavemotion.html

Entities for Sound

ppp in [Pa] ppp = max(p(t))-min(p(t))

prms in [Pa]





T r m s

d t t p T p

2

) ( / 1

REMEMBER THIS SPL = Sound Pressure Level in dB re. 1µPa

(A explosion close by will damage your hearing)

SEL = Sound Exposure Level in [dB re 1 µPa²s]

(Loud sound in a bar will slowly damage your hearing)

Summer Winter

Propagation of sound in shallow water

Winter& Spring Summer & Autumn 50 Hz: dashed 500 Hz: solid Winter: black Summer: blue

Ambient noise in Öresund

Sound pressure dB re 1 µPa

Ambient noise in Öresund

600 m from shipping lane

Ship name Fartygstyp MMSI Speed

• Dist. tol

hydrophon Measured intesity Measured intesity Esitmated intesity @ 1 m Esitmated intesity @ 1 m number (knots) (m) 20-4000 (Hz) 123-132 (Hz) 20-4000 (Hz) 123-132 (Hz) Lillgrund Serviceboat 219010942 9 30 124 89 149 114 Finnpartner Passenger ferry 266262000 12 550 133 102 180 149 Viscaria Tanker 258897000 10 630 121 74 169 122 Finneagle Passenger ferry 265740000 11 620 129 99 176 146

Ambient noise

600 m from shipping lane

Basic physics of underwater acoustics

Measured in dB relative to 1µPa  3 dB is a doubling of pressure, 6 dB ten times larger Sound consists of both pressure variations and particle motion Echoes (reverberation) in shallow water acoustics are common – long reverberation The speed of sound in water is 1500 m/s, in air 350 m/s, localization is done differently underwater The environmental influence is large especially the thermocline and the halocline in the Baltic Sea Distinguish between impulsive and continuous sound

Source level of wind turbine 136 dB re 1μPa for a 150 Hz tone Cumulative effects has to be estimated

Cumulative effects

Sound pressure dB re 1 µPa Ambient

500 turbines 80 turbines

The MSFD Descriptor 11

Indicator 11.1.1:

There are evidences that species react to loud sound sources: Member States have to have a book keeping system to avoid exposures that will harm the marine environment

Indicator 11.2.1: The trend seems to be increasing in many places:

The Member States have to monitor the noise to establish what the trend is

Sources to be included in the Registry

• Airgun: SLz-p > 209 dB re 1 μPa m
• Low-mid frequency sonar: SL > 176 dB re 1 μPa m
• Low-mid freq. acoustic deterrent: SL > 176 dB re 1 μPa m
• Generic non-impulsive sound source: SL > 176 dB re 1 μPa m3
• Explosions: mTNTeq > 8 g
• Generic impulsive sound source SLE > 186 dB re 1 μPa² m² s