On empirical formulae to assess the source level of ships in shallow water with different hydrophone configurations

Over the last decades, actions to safeguard the environment has become a prior concern in the scientific community. Underwater acoustics specialists take part to this initiative by putting effort to reduce the impact of anthropogenic underwater noise on marine fauna. More particularly, commercial shipping has been identified as one of the main sources of noise. Work has been undertaken since the 2010s to define quantities and develop procedures related to ship radiated sound. A standard has been published in 2016 to measure underwater sound radiated from ships in deep waters (ISO 17208-1). The second part of the standard (ISO 17208-2) introduces an empirical correction factor to account for the influence of acoustic reflection on the sea surface, known as the Lloyd's mirror effect. The next step focuses on shallow water measurement, where multiple reflections of the acoustic waves on the sea bottom and surface complexify the propagation. Here, the receivers can be arranged in a vertical array, as for the deep-water procedure, or bottom-mounted. The present work compares different empirical formulae and tests their robustness against different hydrophone configurations. Test cases are solved using numerical simulations and widespread underwater acoustics computational tools (based on wavenumber integration and ray theory).