![]() As an important application of sound propagation modeling, the European Commission recommends that the Member States combine underwater sound measurements and models to ascertain levels and trends of underwater noise in the oceans and coastal areas ( Dekeling et al., 2014). More specifically, the very loud noise of relatively short exposure can harm marine mammals, fish and marine invertebrates (e.g., Hastie et al., 2015 Shannon et al., 2016). Recent research has shown that underwater noise made by human activities, such as seismic airguns, ships, sonars, explosives, or pile drivers, has the potential to impact marine ecosystems. Human activities in the ocean have increasingly added anthropogenic sounds to underwater environments (e.g., Duarte et al., 2021). According to their governing equations and numerical schemes, 3D underwater acoustic models can be divided into three main groups: parabolic equation (PE) models (e.g., Lin and Duda, 2012 Heaney and Campbell, 2016), normal mode models (e.g., Porter, 1992 DeCourcy and Duda, 2020), and ray and beam tracing models (e.g., Porter, 2016 Calazan and RodrÃguez, 2018). Still, simulating underwater sound propagation accurately for fully 3D environments involves significant scientific challenges and can demand high computational costs (e.g., Jensen et al., 2011 Lin et al., 2019). A number of 3D ocean acoustic propagation models have been developed over the past decades (e.g., Jones et al., 1986 Lee et al., 1992 Porter, 1992, Porter, 2016 Bucker, 1994 Smith, 1999 Luo and Schmidt, 2009 Heaney and Campbell, 2016 Lin, 2019 DeCourcy and Duda, 2020). Examples include the assessment of underwater noise induced by offshore wind farms ( Dahl and Dall’Osto, 2017 Lin et al., 2019) and the influence of estuarine salt wedges on sound propagation ( Reeder and Lin, 2019). Numerical models are often used to solve underwater acoustics related problems in realistic complex coastal environments. ![]() In the particular case of coastal seas, a range of physical oceanographic and geological features can cause horizontal reflection, refraction, and diffraction of sound. Three-dimensional (3D) effects can profoundly influence underwater sound propagation and hence soundscape at different scales in the ocean (e.g., Duda et al., 2011 Ballard et al., 2015 Heaney and Campbell, 2016 Reilly et al., 2016 Oliveira and Lin, 2019 Reeder and Lin, 2019). Results emphasize that when choosing an underwater sound propagation model for practical applications in a complex shallow-water environment, a compromise will be made between the numerical model accuracy, computational time, and validity. Indeed, for the complex shallow bathymetry found in some areas of Long Island Sound, it is challenging for the models to track the interference effects in the sound pattern. The TL results from 3D PE simulations indicate that sound propagating along sand bars can experience significant 3D effects. Differences found emerge with (1) increasing the bathymetry complexity, (2) expanding the propagation range, and (3) approaching the limits of model applicability. In general, transmission loss (TL) results provided by the PE, normal mode and beam tracing models tend to agree with each other. Frequencies of 5 Hz are considered in all the simulations. After that, the PE model is utilized to model sound propagation in three realistic local scenarios in the Sound. First, the 2D and 3D versions of the PE model are compared with state-of-the-art normal mode and beam tracing models for two idealized cases representing the local environment in the Sound: (i) a 2D 50-m flat bottom and (ii) a 3D shallow water wedge. In this work, the ability of a parabolic equation (PE) model to simulate sound propagation in the extremely complicated shallow water environment of Long Island Sound (United States east coast) is investigated. Various geological features and coastal oceanographic processes can cause horizontal reflection, refraction, and diffraction of underwater sound. Three-dimensional (3D) effects can profoundly influence underwater sound propagation in shallow-water environments, hence, affecting the underwater soundscape. 3Heat, Light, and Sound Research, Inc., San Diego, CA, United States.2Applied Ocean Physics and Engineering Department, Woods Hole Oceanographic Institution, Woods Hole, MA, United States.1Physics Department, Centre of Environmental and Marine Studies, University of Aveiro, Aveiro, Portugal.
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