Ines Addeo

Human activities have been causing a severe deterioration of the Earth's ecosystem. In recent years, the issue of environmental disaster has become central in the international political debate. One of the most damaged ecosystems is the marine environment and recently the underwater noise has been recognized as one of the pollutants. The latter heavily affects the vital functions of marine organisms. Therefore, it is important to investigate the sources of underwater noise and analyse the acoustic signals they produce. Noise produced by commercial ships is one of the major acoustic pollutants (Hildebrand, 2004), and cavitation plays an important role in this process. Offshore wind farms produce high levels of noise (Copping AE, 2020). Other sources are military sonar, intensive fish farming, drilling, and tools for seismic and geophysical analysis. To address the noise reduction issue, is fundamental to accurately characterize the noise source and reconstruct the propagation of sound waves. There are different techniques for assessing the noise field, and the mostly used are: acoustic analogy theory (AA), Helmholtz equation (HE), wave equation (WE). AA requires the assumption of a homogeneous infinite propagation medium, therefore, it cannot realistically describe the marine environment. When using HE, the acoustic source directivity is ignored. WE is computationally expensive, therefore, it is limited to simple geometries. Thus, the field of underwater noise modelling remains an area that demands substantial investment in research to develop new methods capable of overcoming the limitations of existing techniques.

Our final objectives are: • Construction of a new physical-space model that allows for the description of sound generation and propagation in in large scale domains (basins, gulf, ports) in presence of real acoustic sources. • Creation of detailed sound maps reproducing the major basins to assess the impact of anthropogenic noise on the marine ecosystem. • Development of strategies to reduce anthropogenic underwater noise.

The modelling phase is divided in: numerical simulation of the fluid dynamic field; modelling the acoustic source and the marine geometries; solve the acoustic field and study the propagation of sound waves. We are using Specfem3d software which is commonly used for seismic waves in solid media. It is based on spectral element method which couples the advantage of the finite element formulation for treatment of complex geometry with the accuracy supplied by the spectral representation of the spatial derivatives. Thus, it is possible to consider unstructured meshes, which are fundamental for discretizing the seabed and the coastline.

We expect to obtain detailed sound maps of real basins that can be compared with the ones already produced in important projects (JOMOPANS, SONIC) and the numerical results will be validated with experimental data collected in European projects (Marine Copernicus, SONORA).