et al. 2012) requires the distribution of loud low and mid frequency impulsive sources, in time and space, to be captured as a measure of Good Environmental Status (GES). The MSFD is further described in Chapter 3 Policy and Legislative Context. Pile driving using an impact hammer is considered such a source and is therefore to be included in a UK register of such sounds.
11.
The National Measurement Office, Marine Scotland and The Crown Estate Good Practice Guide for Underwater Noise Measurement (Robinson et al. 2014) describe the metrics which should be used when reporting underwater noise levels. It also provides guidance for the technical requirements for propagation models used for underwater noise. Consistency with these metrics has been maintained throughout this assessment and the guidance relating to the acoustic propagation model has been followed.
9.4.2 Data sources 12. No underwater noise measurement data have been collected for this assessment. Details of the sound propagation modelling and the input data are provided in Appendix 9.1. Data sources relating to the fish and marine mammals assessments are reported in Chapter 11 Fish and Shellfish Ecology and Chapter 12 Marine Mammal Ecology, respectively.
9.4.3 Impact Assessment Methodology
9.4.3.1 Background 13.
By convention, sound levels are expressed in decibels (dB) relative to a reference pressure, which is 1 Pa for underwater sound. Common parameters to describe the received level of a sound pulse are the zero to peak sound pressure level (hereafter referred to as peak pressure level) expressed in dB re 1 Pa, and the sound exposure level (SEL) expressed in dB re 1 Pa2·s which is related to the energy contained in the sound pulse.
14.
The output amplitude of a sound source is commonly described in terms of a source level, which may be considered to be the sound pressure level that would exist at a range of 1m from the acoustic centre of an equivalent simple ‘point’ source which radiates the same acoustic power into the medium as the source in question in the absence of any boundary reflections. As with received level, the source level can be described in terms of peak pressure source level (in dB re 1 μPa·m, often expressed as dB re 1 μPa at 1m) or as an SEL source level (in dB re 1 μPa2·s·m2, often expressed as dB re 1 μPa2·s at 1m). It should be noted that for marine piling, the received level measured at 1m would not be equivalent to the source level due to the complex sound field in such close proximity to the pile.
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 9 Underwater Noise Page 4
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