L4 : Human noise in the Sea Flashcards
1
Q
why is sound important in the sea
A
sound travel 5x faster underwater
- light penetrates only shallow depths
thus sound being main sense for marine organisms
2
Q
sound basics
A
- pressure wave
- measured in frequency (long wavelength = low freq.)
- lower frequencies travel much further than high frequencies
3
Q
sound propagation in the sea
A
speed of sound increases with the increasing water temp, increasing salinity and increasing density
4
Q
Deep sound channel
A
- sound waves in this layer get ‘trapped’ between water layers
- near bermuda, at 1000m
- shallower in temperate waters
- beyond about 60 N or S it reaches the surface
- sound can travel over 1000km
5
Q
natural noise
A
- earthquakes
- ice
- turbulance
- breaking waves
- rain
- bubbles and spray
- marine life…
6
Q
shipping
[anthropgenic noise]
A
- propeller cavitation, flow noise, engine noise
- contributes noise 95-500 Hz (low freq)
- increased low freq. noise to the ocean at a rate of 3d.b per decade (doubling every decade)
7
Q
Seismic Surveys
[anthropgenic noise]
A
- airgun : sends high energy sound into the seabed to find oil, determine seabed etc
- sound concentrated <300 Hz but energy spills into higher frequencies (up to 15 kHz recorded)
8
Q
Naval Sonar
[anthropgenic noise]
A
- use high energy mid/low freq. sonar to find subs
- low freq (LFA) = 100-500 Hz
- mid freq. (MFA) = 2-8 kHz
linked to whale strading and the bends
9
Q
Construction
[anthropgenic noise]
A
- detonations
- pile driving
a. offshore wind farm construction
b. very loud noise
c. 100 Hz - 10 kHz - temp. displacement of marine mammals
10
Q
fisheries
[anthropgenic noise]
A
- sonar to find fish
- acoustic deterrents/pingers to scare marine mammals from nets
11
Q
Science
[anthropgenic noise]
A
- side scan sonar
- fisheries sonar
- ADCP (high freq. sound to measure ocean currents)
- depth sounders
- ATOC
- play back experiments
12
Q
ADCP
A
acoustic doppler current profiler
13
Q
ATOC
A
acoustic thermometry of the oceans climate
14
Q
Noise Legislation
A
- noise classed as pollution under MSFD
- guidelines on shipping noise under IMO
- many species protected under various laws prohibiting harm or injury to protected species
- monitoring & mitigation often required under EIAs
15
Q
IMO
A
international maritime organisation