Underwater Noise Pollution

Underwater Noise Pollution

 


 

Navy SONAR testing

 

The Navy uses two different classes of SONAR, passive and active: Passive sonar listens for sound waves without emitting any sound, while active sonar propagates sound waves through the water. There are three types of active sonar: low, mid, and highfrequency active (LFA, MFA, HFA).

 

MFA and LFA are types of SONAR used by the Navy to locate objects in the water. A loud blast or sound wave is emitted into the ocean and then bounced off of an object. The reflection of the blast, called a "ping", is then listened for to judge the object’s size, distance and sometimes shape. In general, lower frequencies travel longer distances. The “loudness” or amplitude of MFA and LFA sonar is upwards of an astounding 235 dB; the deafening equivalent of a space shuttle at launch. HFA is often used as a deterrent for marine mammals or fish.

 

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Other Sources of Underwater Noise Pollution

 

Large Commercial Ships:

 

Commercial ship traffic has tripled in the last 75 years, resulting in a 3-5 dB increase per decade of noise in the marine environment. A large modern super-tanker reaches a steady-blare of 190 dB or more. This combined with the increasing traffic smothers sounds throughout the natural environment.

 

Underwater Exploration and Mining:

 

As gas and petroleum exploration increase in our oceans, so do seismic surveys. These surveys involve up to 20 high-energy air guns fired for 20-39 milliseconds at a rapid frequency (every 10-12 seconds) as loud as 250 dB. Surveys may last weeks at a time and cover hundreds of square miles, sending noise pollution out thousands of miles. Explosions and detonations involved in testing and research also occur during construction and dismantling of oil platforms. Not only harmful to marine mammals, these noises have proven to affect fisheries in Norway where catch rates of haddock and cod fell 45-70 % in the vicinity of an air gun array (A. Engas et al.1996).