Abstract
An increasing attention has recently been paid to the effect of the underwater noise field generated by ship activities on the marine environment. Although this problem is widely discussed in international treaties and conventions, it has not yet found a consolidated technical-scientific treatment capable of quantifying the level of underwater noise emissions produced by naval systems. As part of a national research collaboration, a novel code has been developed to predict noise propagation according to the Ray Tracing approach. Such optical geometry-based technique allows for calculating the Transmission Loss (TL) trend in its respective contributions: geometrical loss (due to the distance between the source and receiver), dissipation loss (due to the characteristics of the propagation environment), and reflection loss (due to the surfaces that delimit the field). The simulation requires as input parameters the source info as spatial position, frequency, and sound pressure level (SPL) as well as the sea properties like seabed depth, the speed of sound profile, the layers thickness the water column is divided into, the sea salinity, temperature, and pH. The simulation code provides the SPL spatial distribution useful as a fast industrial tool in the future studies addressed to identify the emission limits for the protection of marine wildlife.
Highlights
A topic of scientific interest for many years now is the study of noise propagated in the sea
In 2008, underwater noise was defined as a qualitative parameter of the state of health of the marine environment, requiring Member States to consider the problem and take precautionary measures aimed at containing cross-border pollution emissions (European Community, through the “Marine Strategy Framework Directive” [10])
The Matlab® code developed allows for simulating the mapping of hydrophones positioned at different heights of the seafloor: the focus of authors has been placed on the analysis of noise levels in the Adriatic Sea never presented in literature so far
Summary
A topic of scientific interest for many years now is the study of noise propagated in the sea. The United Nations Convention on the Law of the Sea (UNCLOS) established underwater noise produced by both coastal and offshore anthropogenic activities as a source of pollution of the marine environment [9]. The high-speed noise band is mostly given by some propulsive components with a frequency range above 100 Hz. Experimental field studies have been conducted in order to analyze the formation and propagation of the acoustic waves produced by a small ship in condition of the shallow sea [36]. In the course of this article, a fast methodology for the prediction of the noise emitted by a source will be studied by applying the Ray Tracing theory, useful for calculating the wave propagation paths as a function of characteristic parameters: the different distribution speed of sound, absorption characteristics of the region fluid, and surfaces reflection properties. The results were compared with the Pekeris model [41]: a maximum error of 3 dB was found both at the assigned heights and up to a range of 25 km
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