Abstract
This study is part of the research programme Wozep (‘Wind op Zee Ecologisch Programma’), which investigates the ecological effects of offshore wind energy development in The Netherlands. It addresses the following research questions:
Is it correct to assume that harbour porpoises are more sensitive to the underwater sounds produced by piling for the offshore wind turbine foundations in the North Sea than harbour and grey seals?
Is there a need to incorporate in the impact assessment the frequency spectrum of the piling sound in relation to the frequency sensitive hearing of porpoises and seals? What are the consequences of frequency weighting for the threshold values for hearing loss and behavioural response?
Are the available acoustic models sufficiently accurate to incorporate the frequency weighting in the impact assessment? If not, how can uncertainty be reduced?
These questions will be addressed by a Dutch national expert group on underwater noise, organized by Rijkswaterstaat. TNO was asked to prepare this report as input for the working group meetings.
The following approach has been followed:
1. A review of the available literature on the application of frequency weighting in the assessment of the impact of underwater sound on harbour porpoise (Phocoena phocoena), harbour seal (Phoca vitulina) and grey seal (Halichoerus grypus).
2. A numerical analysis on the available data from measurements and calculations of piling sound, to evaluate the effects of different forms of frequency weighting on impact assessment and threshold levels.
The current version of this report presents the results of the literature review and data analysis. A first attempt to answer the research questions is made in chapter 5. Knowledge gaps and proposals for further research are addressed in Chapter 6.