MODELLING EXPOSURE OF MARINE MAMMALS TO UNDERWATER NOISE FROM PULSED SOURCES IN LONG-DURATION SURVEYS

Résumé

Sound sources, such as airgun arrays, used during exploratory seismic surveys for subsea hydrocarbon deposits are typically towed by a vessel. Multiple arrays and multiple vessels may be used and firing patterns amongst the arrays can be complicated. The animals exposed to these sound fields may move as well. In order to determine the potential impacts of the sounds on animals, a method is needed to estimate received sound levels. Realistic animal movement within the sound field can be simulated, and repeated random sampling (Monte Carlo)—achieved by simulating many animals within an area—used to estimate the sound exposure history of animals during a survey. Monte Carlo methods provide a heuristic approach to determine the probability distribution function (PDF) of complex situations, such as animals moving in a sound field. A greater number of random samples, in this case more simulated animals (animats), better approximates the PDF.
In the early versions of this model development, Jasco utilized some modules from the ESME software workbench (Effects of Sound on the Marine Environment), a package made available by the Boston University Hearing Research Center and the Office of Naval Research, as well as Marine Mammal Movement and Behavior (3MB) model from the National Marine Mammal Foundation. After more experience was gained using ESME in production modelling work, Jasco found it advantageous to implement JEMS (Jasco Exposure Modelling System) a new, more specific program to interface between the animat tracks output by 3MB and the underwater noise field predictions of the Jasco acoustic propagation models, MONM (Marine Operations Noise Model).
This paper will present the reasons why JEMS development was undertaken and an overview of how JEMS solves the exposure modelling problems.