© Q u e e n ’ s P r i n t e r a n d C o n t r o l l e r o f H M S O , 2 0 1 3 . 1 0 6 6 5 / 1 0 1 3 www.npl.co.uk Environmental dependence of underwater sound propagation resulting from impact pile driving Tanja Pangerc 1 , Pete Theobald 1 , Lian Wang 1 , Paul Lepper 2 and Stephen Robinson 1 1 National Physical Laboratory, Hampton Road, Teddington, TW11 0LW, UK 2 School of Electronic, Electrical and Systems Engineering, Loughborough University, Leicestershire, LE11 3TU, UK • Receptor position in the water column is an important consideration. • Sound speed profiles, even in shallow water, can have a significant influence on acoustic propagation. • Variation in sediment properties, typical to the North Sea, result in substantial differences in acoustic propagation ranges for piling noise. References Ainslie, M. A., de Jong, C. A. F., Robinson, S. P. and Lepper, P . A. (2010) What is the Source Level of Pile Driving Noise in Water? Proceedings of the 2nd International Conference on the Effect of Noise on Aquatic Life, Cork, Ireland, August, 2010. Percussive pile driving, often used to install offshore wind turbine foundations, has the potential to radiate high amplitude sound into the water column. The amplitude of the radiated sound will depend on both the sound source characteristics (e.g. frequency, source level) and the propagation environment. Consequently, variation between different offshore wind farms should be expected. Environmental parameters influencing the propagating may include: • Bathymetry • Acoustic properties of the seabed • Properties of the water column • Sea-surface state Propagation loss is frequency dependent. AIM: Illustrate, with modelling, the potential effect of seasonality and sediment type on underwater noise propagation, for common environmental conditions in the UK North Sea, in relation to pile driving. Parameters considered: • Typical parameters consi dered for the North Sea (East Coast of England) • Seasonal sound speed data profiles (WOA2005) • Sediment: sand and gravelly sand • Water depth kept constant (30 m) to reduce variables in the model • Flat sea surface assumed to reduce variables in the model • Sound source based on Ainslie et al. (2012) Numerical propagation model: • Parabolic equation solution propagation model used - RAM (Range-dependent Acoustic Model) (RAMGeo, AcTUP V2.2L) • Source level propagated in third octave bands • Calculation of broadband pulse SEL Spring Summer Autumn Winter Spring Summer Autumn Winter Constant depth and sound speed profile, variable sediment Constant depth, fixed sediment type (gravelly sand), variable sound speed profile Gravelly sand Gravelly sand Sand