From studies in marine biology it is known that the behaviour of large sea mammals as well as fish can be influenced by background noise. Cavitation of ship propellers has been identified as a main source of this background noise. The EU requires Member States to demonstrate that levels of underwater noise do not harm marine life. It is believed that cavitation noise from shipping traffic is largely responsible for low frequency ambient noise, a need has arisen for an improved understanding of the correlation between cavitation and background noise in the seas.
The EU has set out on improving the environment within its member states by adopting the Good Environmental Status. This has been further defined in the Marine Strategy Framework Directive, in which it describes descriptors for measuring the environmental status. One of these descriptors is the underwater noise linked to among others maritime transport. It is stated that the reduction of underwater noise will be a measure for the improvement of the environment.
SONIC will deliver the technical knowledge required for mapping, measuring and mitigating noise from shipping. The results of the SONIC project will contribute to quieting the oceans and improving the well-being of marine life.
The aim of the SONIC project is to develop tools to investigate and mitigate the effects of underwater noise generated by shipping, both in terms of the footprint of an individual ship (a noise footprint) and of the spatial distribution of sound from a large number of ships contribution to the sound (a noise map).
The project's first objective is to enhance the understanding of noise generated by a cavitating ship propeller. The second objective is to validate predictions of noise levels for individual ships, and to classify ships based on simplified noise models. SONICs third objective is to map the noise generated by shipping in general and to propose mitigation measures for quietening the oceans.
The SONIC consortium consists of world-leading hydrodynamic institutes, noise experts, propeller designers, reputable universities with specialised centres in this field, major European shipyards, and a class society; bringing together a wealth of knowledge on propeller cavitation and noise reduction. Interaction with the marine biology network has been established by obtaining necessary input to the project from renowned institutes in the field of marine biology.
Quieting the oceans
Researchers from multiple nations are joining forces to investigate and mitigate the effects of underwater noise generated by shipping.
Cavitation is a noisy, vibration-inducing phenomenon where water ‘cold-boils' at low pressure, causing shock waves when the cavitation bubbles collapse upon entering areas of higher pressure resulting in noise bursts. This underwater noise, created by ever-increasing maritime traffic, may negatively affect large sea mammals and fish.
The EU-funded ‘Suppression of underwater noise induced by cavitation' (SONIC) project aims to understand, map and minimise background noise caused by shipping.
SONIC has brought together world-leading hydrodynamic institutes, noise experts, propeller designers, universities, European shipyards and marine biologists to develop guidelines for determining and mitigating the underwater noise emitted by shipping in the European seas. SONIC has developed techniques to model cavitation noise computationally, and experimentally at model scale. Full scale measurements on a dedicated test vessel as well as close to a busy shipping lane, have also been performed to validate the numerical and experimental techniques.
Project members are also mapping the spatial distribution of sound caused by a single ship (a noise footprint) and sets of ships in an area (a noise map). The Automatic Identification System (AIR) data transmitted by vessels is used with radiated noise models to generate these noise maps.
At the completion of SONIC in 2015, the cavitation noise models will have been validated resulting in guidelines for determining and mitigating the underwater noise levels of ships. The European Commission can use the noise mapping methods to determine the underwater sound levels in European waters.
Quieting the oceans in this way will improve the environmental status of European waters and the welfare of marine life.