Modeling cumulative sound exposure around marine seismic surveys

Abstract

This article presents a method for reducing the computation time required for estimating cumulative sound exposure levels. Sound propagation has to be computed from every source position to every desired receiver location; so if there are many source positions, then the problem can quickly become computationally expensive. The authors' solution to this problem is to extract all possible source-receiver pathways and to cluster these with a self-organizing neural net. Sound propagation is modeled only for the cluster centroids and extrapolated for the entire geographic region. The tool is illustrated for the example of a marine seismic survey over a tropical coral reef. Resident fish species were expected not to flee the reef, but to stay among the corals for the entire duration of the survey. In such cases, the modeling of cumulative sound exposure levels is sometimes requested as part of environmental impact assessments. The tool developed combines a seismic source model, a near-field sound propagation model, and a far-field sound propagation model. The neural network reduces the computation time by a factor of 55. The cost is an error in modeled received levels of less than -1+/-3 dB re 1 microPa(2) s.

The marine soundscape of the Perth Canyon

“…Anthropogenic sources include seismic exploration (Erbe and King, 2009;Greene and Richardson, 1988), pile driving (Erbe, 2009), dredging (Reine et al, 2014), petroleum production operations (Erbe et al, 2013;Wyatt, 2008), equipment such as sonars, echosounders, acoustic tags and pingers (Ainslie, 2010;Erbe and McPherson, 2012), explosions (Soloway and Dahl, 2014), as well as ships of all sizes (Erbe, 2002(Erbe, , 2013aRoss, 1976;Scrimger and Heitmeyer, 1991). Propeller cavitation is typically the strongest source of ship noise from large vessels and exhibits a broadband spectrum, amplitude modulated at the propeller blade rate (i.e.…”

Characterizing anthropogenic noise to improve understanding and management of impacts to wildlife

“…Some studies have summed the SEL over a given period of time to calculate a cumulative sound exposure level (SEL cum ). This provides an exposure under all conditions, stationary or mobile (Erbe & King 2009, Lepper et al 2012.…”

Environmental Assessment for a Marine Geophysical Survey of Parts of the Arctic Ocean, August-September 2010

“…To determine how close an airgun array would need to approach in order to elicit TTS, it is necessary to determine the total energy that a mammal would receive as an airgun array approaches, passes at various CPA distances, and moves away (for example, Erbe and King, 2009). At the present state of knowledge, it is also necessary to assume that the effect is directly related to total received energy even though that energy is received in multiple pulses separated by gaps.…”

“…However, the levels of successive pulses that will be received by a marine mammal that is below the surface as a seismic vessel approaches, passes, and moves away will tend to increase gradually and then decrease gradually, with periodic decreases superimposed on this pattern when the animal comes to the surface to breathe. To estimate how close an odontocete's CPA distance would have to be for the cumulative SEL to exceed 198 dB SEL (M mfweighted), one would (as a minimum) need to allow for the sequence of distances at which airgun shots would occur, and for the dependence of received SEL on distance in the region of the seismic operation (for example, Erbe and King, 2009). …”