Techniques for modeling ocean soundscapes: Detailed description for wind contributions (PDF)

iderius, M., M.A. Ainslie, J. Gebbie, A. Schafke, N. R. Chapman, S.B. Martin, and K.L. Gemba

The Journal of the Acoustical Society of America 156(5): 3446–3458 (2024)

DOI: 10.1121/10.0034236

Wind over the ocean creates breaking waves that generate air-filled bubbles, which radiate underwater sound. This wind-generated sound is a significant component of the ocean soundscape, and models are essential for understanding and predicting its impact. Models for predicting sound pressure level (SPL) from wind have been studied for many years. However, the terminology and definitions behind modeling approaches have not been unified, and ambiguity has led to differences in predicted SPL. The 2022 Ambient Sound Modeling Workshop was organized to compare ambient sound modeling approaches from different researchers. The main goal of the workshop was to quantify differences in predicted SPL and related quantities for different approaches and, to the extent possible, determine the cause of the differences for a specific, well-defined scenario. Results revealed a variation of approximately 6 dB across different research groups, with differences reaching up to 10 dB in some cases compared to the benchmark results described in this paper. These variations stemmed from differing methodologies and underlying assumptions. In this paper, step-by-step guidance is given for modeling SPL due to wind. The workshop test case will be described, and results from the modeling approaches described here will be compared with those from the workshop participants.

Verifying models of the underwater soundscape from wind and ships with benchmark scenario (PDF)

Martin, S.B., M. Siderius, M.A. Ainslie, M.B. Halvorsen, L. Hatch, M.K. Prior, D. Brooker, J. Caplinger, C. Erbe, J. Gebbie, K. D. Heaney, A.O. MacGillivray, M. Matthews, V.O. Oppeneer, A. Schafke,  R.P. Schoeman, and H.O. Sertlek

The Journal of the Acoustical Society of America 156(5): 3422–3438 (2024)

DOI: 10.1121/10.0026597

Models of the underwater acoustic soundscape are important for evaluating the effects of human generated sounds on marine life. The performance of models can be validated against measurements or verified against each other for consistency. A verification workshop was held to compare models that predict the soundscape from wind and vessels and estimate detection ranges for a submerged target. Eight modeling groups participated in the workshop which predicted sound levels with observation windows of 1 min and 1 km2. Substantial differences were found in how modelers computed the propagation losses for decidecade bands and estimated the source level of wind. Further investigations resulted in recommendations on best practices. Choices of temporal and spatial modeling resolution affected the estimates of metrics proportional to total sound energy more than distributions of sound pressure level. Deeper receivers were less sensitive to these parameters than shallow ones. A temporal resolution of 1 min and spatial resolution of 100 m is recommended. Models that follow the recommendations will yield similar results. The detection range of underwater targets is highly variable when the ambient noise depends on moving noise sources. Future work to verify models against data and understand model uncertainty is recommended.

Range versus frequency averaging of underwater propagation loss for soundscape modeling (PDF)

Zykov, M.M., and S.B. Martin

The Journal of the Acoustical Society of America 156(5): 3439–3445 (2024)

DOI: 10.1121/10.0030475

Guidance on efficient methods is needed for the practical application of modeling the sound field from broadband sources such as vessels, seismic surveys, and construction activities. These sound field models are employed for estimating how changes in the soundscape will affect marine life. For efficiency, acoustic propagation modeling is often performed in bands (decidecade or 1/3-octave), where propagation loss modeled for central frequency is assumed to represent an average propagation loss in the band. This shortcut comes at the expense of accuracy, which can be rectified by averaging the propagation loss across many frequencies in the band. Alternately, the equivalence of range and frequency averaging was shown by Harrison and Harrison [J. Acoust. Soc. Am. 97, 1314–1317 (1995)]. However, when and how to apply range averaging required further investigations. A simple environment with a flat sandy bottom and an isovelocity water-column sound speed profile was considered to test the agreement between the range and frequency averages for decidecade bands typically considered in soundscape modelling (10–1000 Hz). The optimal range smoothing window is a Gaussian window with a width of 10%–16% of the range from the source that switches to a width fixed beyond 20 km distance from the source.

Sound emissions from Ultrasonic Antifouling equipment (PDF)

Martin, S.B., A.O. MacGillivray, J.D. Wood, K.B. Trounce, D.J. Tollit, K. Angadi

The Effects of Noise on Aquatic Life (2024)

DOI: 10.1007/978-3-031-50256-9_102

The Vancouver-Fraser Port Authority-led Enhanced Cetacean Habitat and Observation (ECHO) Program has managed underwater listening stations (ULSs) on the approach to the Port of Vancouver since 2015, measuring the sound levels generated by thousands of vessels. Since 2017, these systems have measured at or above a 128 kHz sampling rate. Anomalously high sound levels were observed in 212 of the measured ships signatures at frequencies typically associated with navigational, fisheries, and scientific sonars. Sixty-one of these detections were found to originate from a novel continuous sound source in the 20–30 kHz frequency range. During a separate underwater noise monitoring program, a similar high-frequency continuous sound source was identified proximate to a berthed vessel. The vessel engineer identified it as an ultrasonic antifouling system. The sounds from these systems are detectable at 4–6 km from the vessels in deep water. The measurements indicate that echolocation by lower-frequency delphinids, such as killer whales, may be completely masked when a ship is 3 km away and that porpoises flee from the source at distances of 1.5 km. In shallow waters, a porpoise 70 m from the source is predicted to experience temporary threshold shift (TTS) after 1–2 s, and permanent threshold shift (PTS) after 200 s. It is recommended that use of these systems be restricted or prohibited when there is a possibility of exposing marine mammals to potentially harmful sound levels.

Recommendations on bioacoustical metrics relevant for regulating exposure to anthropogenic underwater sound (PDF)

Klaus, L., A.O. MacGillivray, M.B. Halvorsen, M.A. Ainslie, D. G. Zeddies, and J. A. Sisneros

The Journal of the Acoustical Society of America 156(4): 2508–2526 (2024)

DOI: 10.1121/10.0028586

Metrics to be used in noise impact assessment must integrate the physical acoustic characteristics of the sound field with relevant biology of animals. Several metrics have been established to determine and regulate underwater noise exposure to aquatic fauna. However, recent advances in understanding cause-effect relationships indicate that additional metrics are needed to fully describe and quantify the impact of sound fields on aquatic fauna. Existing regulations have primarily focused on marine mammals and are based on the dichotomy of sound types as being either impulsive or non-impulsive. This classification of sound types, however, is overly simplistic and insufficient for adequate impact assessments of sound on animals. It is recommended that the definition of impulsiveness be refined by incorporating kurtosis as an additional parameter and applying an appropriate conversion factor. Auditory frequency weighting functions, which scale the importance of particular sound frequencies to account for an animal's sensitivity to those frequencies, should be applied. Minimum phase filters are recommended for calculating weighted sound pressure. Temporal observation windows should be reported as signal duration influences its detectability by animals. Acknowledging that auditory integration time differs across species and is frequency dependent, standardized temporal integration windows are proposed for various signal types.

Source and propagation modelling scenarios for environmental impact assessment: Model verification (PDF)

Ainslie, M. A., R.M. Laws, M.J. Smith, A.O. MacGillivray

The Journal of the Acoustical Society of America 156(3): 1489–1508 (2024)

DOI: 10.1121/10.0028135

Evaluation of possible effects of underwater sound on aquatic life requires quantification of the sound field. A marine sound source and propagation modelling workshop took place in June 2022, whose objectives were to facilitate the evaluation of source and propagation models and to identify relevant metrics for environmental impact assessment. The scope of the workshop included model verification (model-model comparison) and model validation (model-measurement comparison) for multiple sources, including airguns, a low-frequency multi-beam echo sounder, and a surface vessel. Several verification scenarios were specified for the workshop; these are described herein.

Modeling the underwater sound of floating offshore windfarms in the Central Mediterranean Sea (PDF)

Baldachini, M., R.D.J. Burns, G. Buscaino, E. Papale, R. Racca, M.A. Wood, and F. Pace

Journal of Marine Science and Engineering 12(9): 1495 (2024)

DOI: 10.3390/jmse12091495

In the shift toward sustainable energy production, offshore wind power has experienced notable expansion. Several projects to install floating offshore wind farms in European waters, ranging from a few to hundreds of turbines, are currently in the planning stage. The underwater operational sound generated by these floating turbines has the potential to affect marine ecosystems, although the extent of this impact remains underexplored. This study models the sound radiated by three planned floating wind farms in the Strait of Sicily (Italy), an area of significant interest for such developments. These wind farms vary in size (from 250 MW to 2800 MW) and environmental characteristics, including bathymetry and seabed substrates. Propagation losses were modeled in one-third-octave bands using JASCO Applied Sciences’ Marine Operations Noise Model, which is based on the parabolic equation method, combined with the BELLHOP beam-tracing model. Two sound speed profiles, corresponding to winter and summer, were applied to simulate seasonal variations in sound propagation. Additionally, sound from an offshore supply ship was incorporated with one of these wind farms to simulate maintenance operations. Results indicate that sound from operating wind farms could reach a broadband sound pressure level (Lp) of 100 dB re 1 µPa as far as 67 km from the wind farm. Nevertheless, this sound level is generally lower than the ambient sound in areas with intense shipping traffic. The findings are discussed in relation to local background sound levels and current guidelines and regulations. The implications for environmental management include the need for comprehensive monitoring and mitigation strategies to protect marine ecosystems from potential acoustic disturbances.

Regional soundscape modeling of the Atlantic Outer Continental Shelf (PDF)

Heaney, K.D., M. Ainslie, J. Murray, A.J. Heaney, J. Miksis-Olds, B. Martin

The Journal of the Acoustical Society of America 156, 378-390 (2024)

DOI: 10.1121/10.0026476

The ocean soundscape is a complex superposition of sound from natural and anthropogenic sources. Recent advances in acoustic remote sensing and marine bioacoustics have highlighted how animals use their soundscape and how the background sound levels are influenced by human activities. In this paper, developments in computational ocean acoustics, remote sensing, and oceanographic modeling are combined to generate modelled sound fields at multiple scales in time and space. Source mechanisms include surface shipping, surface wind, and wave fields. A basin scale model is presented and applied to the United States Atlantic Outer Continental Shelf (OCS). For model-data comparison at a single hydrophone location, the model is run for a single receiver position. Environmental and source model uncertainty is included in the site-specific modeling of the soundscape. An inversion of the local sediment type is made for a set of sites in the OCS. After performing this inversion, the qualitative comparison of the modelled sound pressure level (SPL) time series and observed SPL is excellent. The quantitative differences in the mean root mean square error between the model and data is less than 3 dB for most sites and frequencies above 90 Hz.

Three-dimensional modelling of underwater noise produced by a bulk carrier vessel and estimation of its environmental impact (PDF)

Petrov, S.P, A.G. Tyshchenko, and A.O. MacGillivray

The Journal of the Acoustical Society of America 155 (6): 3702–3714 (2024)

DOI: 10.1121/10.0026238

This study presents the results of three-dimensional (3D) propagation modeling of noise from a transiting bulk carrier vessel. In the simulated scenario, the surface vessel is moving past a bottom-mounted hydrophone system. Sound levels are estimated in decidecade frequency bands as the vessel transits past the hydrophone, and the simulation results are compared against real measured data. The modelling is performed using the program AMPLE, which is based on the wide-angle mode parabolic equation theory for simulating 3D broadband acoustic fields in a shallow sea. The model is used to investigate the effect of 3D phenomena on the surface vessel sound propagation. It is shown that an inaccuracy of the noise simulation associated with the use of a two-dimensional model can be as high as 7–10 dB for certain distances and for frequency bands over which a major part of the source energy is distributed. An approach to the selection of data-adjusted media parameters based on the Bayesian optimization is suggested, and the influence of the various parameters on the sound levels is discussed.

Acoustic occurrence of beaked whales off eastern Canada, 2015–2017 (PDF)

Delarue, J.J.-Y., H.B. Moors-Murphy, K.A. Kowarski, E.E. Maxner, G.E. Davis, J.E. Stanistreet, and S.B. Martin

Endangered Species Research 53: 439–466 (2024)

DOI: 10.3354/esr01314.

Several beaked whale species occur off eastern Canada. However, except for the northern bottlenose whale (NBW; Hyperoodon ampullatus), their distribution and annual occurrence remain largely unknown, which complicates management efforts to assess the status of poorly known species and effectively protect those species considered at risk. The main objective of this paper is to provide a year-round and pluriannual description of the minimum acoustic occurrence of the NBW, Sowerby’s (SBW; Mesoplodon bidens), Cuvier’s (CBW; Ziphius cavirostris), True’s (TBW; M. mirus) and Gervais’ (GBW; M. europaeus) beaked whales. Twenty-five acoustic recorders were deployed off eastern Canada between May 2015 and November 2017. Beaked whale echolocation clicks were detected using a combination of automated detectors and manual validation at 12 of these stations. Detections were generally restricted to deep continental slope waters. All detected species occurred in the southern part of the study area (off the Scotian Shelf and southern Grand Banks), while only NBWs were detected at the northern edge, off southern Labrador. Clicks identified as TBW or GBW were restricted to, but occurred annually in, the southern areas. All other species were present, at least seasonally, east and north of the Grand Banks. NBWs occurred every day in the Gully Canyon, where SBWs also occurred regularly. While these results should be interpreted as minimum species presence and considered with regards to detector performance, they provide important information regarding beaked whales’ use of areas off eastern Canada where these species have generally received no or very limited monitoring effort.

Mapping past and future shipping noise in European seas (PDF)

Recca, R., M.A. Ainslie, J. Bosschers, M. Hermans, T. Lloyd, A.O. MacGillivray, F. Pace, M. Schuster, O. Sertlek and M. Wood

The Journal of the Acoustical Society of America 155, A199 (2024)

DOI: 10.1121/10.0027298

Against the backdrop of a steadily increasing demand for sea transport of goods and people, the development of a reliable marine shipping soundscape model is an essential planning requirement to assess the effect on ocean noise of operational and technological changes aimed at mitigating the environmental impact of the shipping sector. The NAVISON (Navis Sonus) project, conducted with the support of the European Maritime Safety Agency, employs a specially developed parametric vessel source model with the objective of producing shipping sound maps in European seas for past, present, and potential future conditions over a time span from 2016 to 2050. The source model is combined with historical ship tracking data from the automated identification system (AIS), or projected shipping densities and mitigation scenarios, to calculate spatial ship noise emissions data for input to a sound mapping tool. The mapping tool computes underwater sound propagation using the parabolic-equation method, drawing upon ocean-scale databases of bathymetric, oceanographic, and sediment properties. Project outputs are provided as map layers of sound pressure level and sound energy according to vessel type, season, region, year, and operational conditions; from these layers, maps can be generated for user-specified combinations of mitigation measures. Maps are presented in two frequency bands (centred at 63 Hz and 125 Hz) selected for assessing Good Environmental Status in the context of the European Union’s Marine Strategy Framework Directive.

Source level of wind-generated ambient sound in the ocean (PDF)

Chapman, N.R., M.A. Ainslie, M. Siderius

JASA Express Letter 4, 010001 (2024)

DOI: 10.1121/10.0024517

Inference of source levels for ambient ocean sound from local wind at the sea surface requires an assumption about the nature of the sound source. Depending upon the assumptions made about the nature of the sound source, whether monopole or dipole distributions, the estimated source levels from different research groups are different by several decibels over the frequency band 10–350 Hz. This paper revisits the research issues of source level of local wind-generated sound and shows that the differences in estimated source levels can be understood through a simple analysis of the source assumptions.

Soundscape of the Northeast Pacific Ocean revisited (PDF)

Ainslie, M.A. , R.K. Andrew, P.L. Tyack , M.B. Halvorsen , J.M. Eickmeier , A.O. MacGillivray , S.L. Nedelec , and S.P. Robinson

The Effects of Noise on Aquatic Life (2024)

DOI: 10.1007/978-3-031-50256-9_2

The measured changes in northeast (NE) Pacific Ocean ambient sound levels in the 63–125 Hz bands are explained by the contribution from shipping to the sound energy budget using a globally averaged sound energy model. The energy model fails to identify the dominant source of sound in the 32 and 40 Hz bands because its estimates deviate from the measured levels. More research is required to resolve this discrepancy. Ships in cold deep water contribute more to ambient sound than in warm shallow water. This suggests a potential mitigation action for the NE Pacific Ocean.

Ship source measurement in shallow water using an enhanced seabed critical angle method (PDF)

Ainslie, M.A., A.O. Macgillivray, R. Yubero, C.D. Jong, L.S. Wang

DOI: 10.25144/22249

Distant ships are a dominant source of ambient underwater sound at low frequency (50–100 Hz),1, 2 while nearby ships can cause disturbance at frequencies of multiple kilohertz.3 Measurement of a ship’s source level (SL) is needed for soundscape prediction, for quiet ship certification and for validation of prediction models. An international measurement standard exists for the determination of SL using deep water measurements (ISO 17208-24). A draft international standard (DIS) for measuring SL in shallow water, currently under development (ISO/DIS 17208-35), needs an SL formula that is both accurate and straightforward to implement.