Man-Made Noise in the Ocean

Sound is the only form of energy that will propagate reliably underwater, and for this reason it is used by aquatic animals for imaging, navigation and communication. Man also uses sound for the same reasons underwater, and additionally generates noise as a byproduct of offshore activity.

When sound is generated underwater, it will have a relatively high level near the source. The level of sound will be attenuated as the sound propagates away from the source, and at some distance it will decay to the level of the background noise in the ocean. The distance within which this will occur, and hence the range within which environmental effects could occur, will depend both on the level of sound generated by the source and on the rate at which the sound decays. These two parameters are therefore of great importance and have become known as the Source Level and Transmission Loss. The way in which the Source Level and Transmission Loss are measured or estimated has a bearing on the applicability of the results to other situations. Those not familiar with these concepts might wish to read the section on measurement of sound underwater.

On land, a wide range of measurements have been taken of the noise levels from all categories of man-made noise. Generally however, there is a lack of the equivalent information for underwater noise, although as a result of environmental pressures some measurements are now being made of noise from activities related to petrochemical exploration and exploitation. There are three main reasons for this:

  1. The lack, to date, of any clear need for taking measurements except for military applications
  2. The difficulty and expense of taking underwater measurements
  3. The lack of any well established criteria by which any measurements taken could be judged

This report has been produced as an initial step in remedying the lack of information; it summarises the information that is currently available in the public domain on man-made noise underwater.

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