Underwater Noise Measurement

Noise on land

The excessive and long exposure to noise in diferent areas of our live from work to our homes has various implications on our health. The most part of noise comes from industrial activity, densely populated areas and various forms of transport.

Noise in the ocean

An increase in noise generated by human activity (anthropogenic noise) on land has been followed by an increase of underwater noise at sea. Since the industrial revolution the levels of noise in the ocean has steadily increased due to the increase of industry and transport such as:

• Marine Transport (Container ships, Oil tankers, Ferries, ...)
• Exploration of oil and gas
• Military activity through the use of high power active sonars
• Fishing industry including shipping and coastal fish farms
• Various types of coastal construction

Cetaceans and underwater noise

Cetaceans (like dolphins and whales) depend on the sound they send and receive to search for food, mating, detection of predators and comunication. Cetaceans use the eco of the sound they send to locate for example fish. Anthropogenic noise can mask the sound sent by these animals to such a point that they can no longer hear their own echo or those of their own species. The problem of underwater noise became more apparent when whales stranded on beaches disoriented and some with internal organ bleeding and failure.

Legislation

In Europe we are seeing an increased interest to legislate and regulate underwater noise. In december 2007 the european comission aproved the first directive which reconizes underwater sound as a form of polution in the ocean, which must be monitored to achieve the general objectives of ambiental quality by 2020. Currently environmental impact studies recommend the need to monitor the contribution of a certain activity in terms of underwater noise.

Our service...

... includes measurements in situ which will be performed in a pre-determined area. Each measurement point is performed at various depths as underwater sound can vary significantly along depths. Using these measurements and with a knowledge of the bathymetry of the area of observation, an underwater acoustic propagation model is used to generate an underwater noise map in depths and distance.

- The in situ Measurements

Our compact measurement equipment is composed of a vertical array of reconfigurable hydrophones. This equipment permits operations in any type of ship or vessel and gives us the possibility to be prepared at any time to perform measurements as they are requested.

- The Noise Maps

The analysis of the acquired signals is performed in such a way as to determine the distribution of energy:

• in frequency
• in depth
• across the area of interest.

As it can be very expensive to measure noise in large areas of the ocean, the underwater acoustic propagation models are of great importance in the creation of underwater noise maps.