Exposure radial distances

• Published in: The Journal of the Acoustical Society of America 2021-10, Vol.150 (4), p.A325-A325
• Main Authors: Küsel, Elizabeth T., Weirathmueller, Michelle, Zeddies, David
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/10.0008451

During offshore construction activities that produce underwater sound, mitigation zones are established to define protective monitoring areas for fauna in the vicinity and to establish whether animals may be exposed to sound levels exceeding regulatory criteria. Traditionally, mitigation zones have been determined by estimating the range within which the sound levels remain above given thresholds. These statically defined “acoustic ranges” have drawbacks, especially for criteria based on cumulative metrics such as SEL for marine mammal injury. A threshold distance derived solely from the acoustic footprint of a source is inadequate in establishing whether an animal moving through a (possibly time-varying) sound field would exceed a time-dependent exposure criterion. An approach to defining mitigation zones based on an understanding of the animals’ movement relative to the sound source overcomes the limitations of the static range calculation. The radial distance from a source that accounts for the exposures above threshold, or 'exposure range', can be estimated statistically from path-dependent sound exposure estimates generated through animal movement modeling. Exposure ranges can be calculated by this method also for moving and multiple sources. We present example scenarios comparing acoustic and exposure ranges in the context of seismic surveys and pile driving activities.