Research Document - 2009/060
The Use Of Sound Propagation Models To Determine Safe Distances From A Seismic Sound Energy Source
By J.W. Lawson
Abstract
To assess how seismic sounds used in petroleum exploration may affect wildlife, it is necessary to estimate received sound levels for the variety of ranges and depths where animals might be located. The apparent loudness of a noise source is determined by the radiated acoustic power, the propagation efficiency, the ambient noise, and the hearing sensitivity of the subject species. The amplitude of seismic sounds usually declines with distance from source, and is largely dependent on the frequency characteristics of the signal. Several factors determine the amount of weakening of seismic array sounds with distance including geometrical spreading, transmission/reflection, absorption, and scattering. Information on geology, seabed characteristics, sediment properties, and bathymetry are critical in determining acoustic propagation losses and received sound pressure levels. Sound propagation and ambient noise conditions are highly variable within and among areas, and a pan-regional “one-criteria-fits-all” regulatory approach is likely not a risk-averse management approach. Studies described in this document will support a conclusion that, while model predictions can be useful for planning and for preparing environmental impact statements, given the discrepancies between modelled and measured sound propagation it is advisable to obtain relevant empirical data as well. The document describes approaches that could improve the effectiveness of seismic sound modelling.
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