In 2012 a seismic survey campaign involving four vessels was conducted in Baffin Bay, West Greenland. Long-distance (150 km) pre-survey acoustic modeling was performed in accordance with regulatory requirements. Four acoustic recorders, three with hydrophones at 100, 200, and 400 m depths, measured ambient and anthropogenic sound during the survey. Additional recordings without the surveys were made from September 2013 to September 2014. The results show that (1) the soundscape of Baffin Bay is typical for open ocean environments and Melville Bay's soundscape is dominated by glacial ice noise; (2) there are distinct multipath arrivals of seismic pulses 40 km from the array; (3) seismic sound levels vary little as a function of depth; (4) high fidelity pre-survey acoustic propagation modeling produced reliable results; (5) the daily SEL did not exceed regulatory thresholds and were different using Southall, Bowles, Ellison, Finneran, Gentry, Greene, Kastak, Ketten, Miller, Nachtigall, Richardson, Thomas, and Tyack [(2007) Aquat. Mamm. 33, 411-521] or NOAA weightings [National Marine Fisheries Service (2016). NOAA Technical Memorandum NMFS-OPR-55, p. 178]; (6) fluctuations of SPL with range were better described by additive models than linear regression; and (7) the survey increased the 1-min SPL by 28 dB, with most of the energy below 100 Hz; energy in the 16 000 Hz octave band was 20 dB above the ambient background 6 km from the source.
Concerns about the potential environmental impacts of geophysical surveys using air gun sources, coupled with advances in geophysical surveying technology and data processing, are driving research and development of commercially viable alternative technologies such as marine vibroseis (MV). MV systems produce controllable acoustic signals through volume displacement of water using a vibrating plate or shell. MV sources generally produce lower acoustic pressure and reduced bandwidth (spectral content) compared to air gun sources, but to be effective sources for geophysical surveys they typically produce longer duration signals with short inter-signal periods. Few studies have evaluated the potential effects of MV system use on marine fauna. In this desktop study, potential acoustic exposure of marine mammals was estimated for MV and air gun arrays by modeling the source signal, sound propagation, and animal movement in representative survey scenarios. In the scenarios, few marine mammals could be expected to be exposed to potentially injurious sound levels for either source type, but fewer were predicted for MV arrays than air gun arrays. The estimated number of marine mammals exposed to sound levels associated with behavioral disturbance depended on the selection of evaluation criteria. More behavioral disturbance was predicted for MV arrays compared to air gun arrays using a single threshold sound pressure level (SPL), while the opposite result was found when using frequency-weighted sound fields and a multiple-step, probabilistic, threshold function.
The term listening area, refers to the region of ocean over which sources of sound can be detected by an animal at the center of the space. The lost listening area assessment method has been applied to in-air sounds for a noise effects assessment on birds but not, in our knowledge, previously to the assessment of underwater noise effects on marine mammals. The lost listening area method calculates a fractional reduction in listening area due to the addition of anthropogenic noise to ambient noise. It does not provide absolute areas or volumes of space, as does the communication space method; however, a benefit of the lost listening area method is that it does not rely on source levels of the sounds of interest. Instead, the method depends only on the rate of sound transmission loss. We present a preliminary application of the method from an assessment of “cumulative and chronic effects” of noise produced by oil and gas exploration activities used in the National Marine Fisheries Service's Effects of Oil and Gas Exploration in the Arctic Ocean Final Programmatic Environmental Impact Statement.
In this paper, we compare airgun sound levels measured during an offshore seismic survey to acoustic model predictions. The survey occurred in deep water (>650 m), on and beyond the continental slope in the Canadian Beaufort Sea. The modeling was performed with JASCO Applied Sciences' Marine Operations Noise Model, which uses a parabolic-equation-based algorithm to predict N×2 D sound propagation in ocean environments. Sound levels were measured with up to five calibrated Autonomous Multichannel Acoustic Recorders at distances of 50 to 50,000 m from the airgun array in water depths between 50 and 1,500 m. The sound levels were measured in both the broadside (across-track) and endfire (along-track) directions. The high-resolution digital recordings of seismic sounds were analyzed to determine peak and root-meansquare sound pressure levels and sound exposure levels as functions of range from the airgun array, and compared to the model results. Although the modeled sound levels were generally conservative, the model results accurately predicted the existence of a shadow zone and the overall transmission loss trend. FIGURE 6. Comparison between modeled and measured sound speed profiles in the water column for the intermediate (500-1000 m; left) and deep (>1000 m; right) water regimes.Agreement between the modeled and measured sound levels was better for the SEL metric than for the rms SPL metric. This difference shows that the modeling of SEL is more robust against environmental error than rms SPL. Future research by JASCO will focus on improved methods for estimating underwater sound levels from impulsive sources, like airgun arrays.
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