flattening of equal-loudness contours for high-amplitude sounds, although these are currently being revised by NOAA (NOAA 2013). The ‘M-weighting’ filters are plotted for each functional hearing group (as outlined in Table 9.1) in Plate 9.3.
Plate 9.3. The M-weighting functions taken from Southall et al. (2007).
9.5.3.1 Injury (Marine Mammals) 61.
The criteria for injury outlined by Southall et al. (2007) consider PTS-onset to constitute injury as sound induced PTS represents irreversible damage to the cochlear hair cells, as opposed to TTS which represents merely fatigue. As PTS has not been measured in marine mammals, the injury criteria are estimated from TTS- onset measurements and knowledge of the rate of TTS growth with increasing exposure levels above the level eliciting TTS-onset. It is assumed that a sound exposure capable of inducing 40dB of TTS will cause PTS-onset, based on available data from terrestrial mammals. The Marine Mammal Noise Exposure Criteria consider three sound types which cover the range of sound sources to which marine mammals might be exposed. These are defined as: i) Single pulses; ii) Multiple pulses; and iii) Nonpulses. Marine piling strikes (i.e., not a single pile strike) are defined by Southall et al. (2007) as multiple pulses. The relevant injury criteria for multiple pulses as stated by Southall et al. (2007) are given below:
•
Injury criteria for low, mid and high-frequency cetaceans: o SPL injury criteria: 230dB re 1 μPa (peak) (flat, un-weighted)
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm Appendix 9.1 Underwater Noise Modelling 21
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