Definition and results of test cases for shipping sound maps

The SONIC (Suppression Of underwater Noise Induced by Cavitation) and AQUO (Achieve QUieter Oceans by shipping noise footprint reduction) projects were awarded within the European Seventh Framework Program to develop tools to investigate and mitigate the effects of underwater sound generated by shipping activities on marine life. Model generated sound maps were identified by the European Commission as a monitoring tool to complement measurements. Sound mapping tools are being developed to provide a representation of shipping sound that is both meaningful to policy makers without requiring a background in acoustics and representative of the phenomena relevant to environmental impact. The accuracy of the end result depends on the quality of the source description as well as that of the propagation model used to compute the sources' combined contributions. In this paper we concentrate on the propagation models used for this purpose. A shipping sound map is usually expected to cover a large geographical area, including a large number of sources radiating sound over a broadband spectrum of frequencies. These requirements place restrictions on the choice of a propagation model. The challenges specific to computation of sound maps and the variety of possible approaches available to address them make it worthwhile to compare the output of different approaches, as well as with reference model solutions when available. For this purpose, five test cases were defined by scientists of the AQUO (“Achieve QUieter Oceans by shipping noise footprint reduction”) and SONIC (“Suppression Of underwater Noise Induced by Cavitation”) consortia. These test cases, defined with increased complexity are specified in this paper and presented with example solutions computed with a variety of models. The purpose of these test cases and associated results is to facilitate evaluation of a given sound map computation system.