Underwater acoustics

Mis à jour le 19/07/2024

The marine environment is an excellent guide for sound waves, which can propagate over hundreds of kilometers, whereas light only penetrates a few meters. Like lighthouses in the fog, when a sound wave travels through the ocean, it is reflected at the surface or on the seabed. The backscattered energy is called reverberation.

However, the propagation of waves depends on environmental conditions such as depth, nature of the bottom, temperature, salinity, pressure and chemical constitution of seawater.

The sources are also of different natures: biological, geophonic and anthropogenic. Understanding the underwater soundscape requires mastery of all these parameters. This is a major challenge when it comes to understanding the environment.

©Shom - Acoustic propagation

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©Shom - Ambient noise linked to maritime traffic

Estimation of underwater ambient noise and reverberation

The Shom carries out statistical calculations of ambient underwater noise for all the world's seas.

Underwater noise is mainly related to maritime traffic, sea surface agitation and environmental propagation conditions./p>

Underwater reverberation is also a parameter that needs to be mastered when searching for a submarine using active sonar.

Physical measurements

Acoustic measurement using hydrophones is an effective way of gaining a general overview of the environment. In particular, it can be used to validate modeling results and assess temporal variability.

The Shom carries out underwater ambient noise measurement campaigns over long periods, using dedicated scientific equipment such as fixed or drifting buoys fitted with high-quality hydrophones.

Support for public sea and coastal policies

Many marine species exploit this property of the ocean to communicate, locate themselves or even spot their prey. Underwater noise pollution generated by human activities could endanger the health of ecosystems, whose scales of adaptation are not always as rapid as the changes initiated by our societies.

This ecological risk is recognized in Europe by the Marine Strategy Framework Directive (MSFD). Shom provides scientific support for understanding and defining this risk, as well as logistical support with the establishment of a large network of hydrophones. He participates in the European technical group on noise pollution (TG Noise).

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