Ship underwater noise emissions: uncertainties in the measurements and in the effects on the marine environment

The underwater noise radiated by ships has been with increasing emphasis included in the list of emissions into the ambient that need to be evaluated and controlled. While from point of view of international treaties and conventions this general goal is now well assessed, from a technical point of view the quantification of the impact of underwater noise emissions from ships is not yet consolidated. The general increase of the background noise in the oceans due to the diffused shipping activity is an objective datum, but how this noise is radiated by ships and how it affects globally and locally the marine wildlife are not yet clear subjects. From the point of view of the models to be used for the assessment, two areas in particular present significant uncertainties: the characterisation of the ship source and the quantification of the noise effects on the marine fauna. Both aspects need to be handled at an experimental level and they are intimately connected, as a proper characterisation of the source levels depends on which effects of the radiation need to be modelled. The paper focuses on the present situation in the two fields, highlighting the areas that still need to be investigated in order to set a consistent normative framework for achieving the objectives.