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Literature179 15beyond the zone of possible physical injury, where thenumber may not be optimum to describe an animal’sresponse to noise. This has several reasons: First, thenumber is an unweighted broadband level, with allfrequency components of the sound treated equally.But an animal’s auditory system is not equally sensitiveto all frequencies. And noise mitigation techniqueslike bubble curtains do not reduce the level ofall frequency components by the same amount; theyalter the shape of the frequency spectrum. Hence ifthe efficacy of mitigation is described in terms of thebroadband level, this may not adequately reflect theimprovement for the animals. Secondly, unlike withthe SEL, an animal’s auditory system does not averagethe sound energy over one second to produce a‘loudness’ sensation (actually the averaging time ofa porpoise’s hearing system is much shorter, in theorder of 0.1 second). And finally, the installation of apile needs more than one pile driving strike. That is,the parameter ‘impact duration’, which is not unlikelyto affect the pressure on the marine environment, isnot reflected in the current standard. Hence a futuretask should be to develop a noise descriptor that ismore closely related to animals’ perception of sound.15.5 AcknowledgementsSpecial thanks to: R. Matuschek, B. Meenen, D. Galinski,A. Diederichs, G. Nehls, K. Blasche, T. Verfuß,C. Honnef, and the crews of R/V Tine Bødkerand F/V Orion.Measuring instruction for underwatersound monitoringAnika BeiersdorfAs part of licensing procedures and during theconstruction and operation of offshore installations,it is essential to analyse the impact ofunderwater noise on the marine environment.The temporal and spatial scope of acoustic investigationsis laid down in the BSH ‘Standard forEnvironmental Impact Assessment’ (StUK4, BSH2013). This requires underwater sound measurementsto be carried out prior to construction,during construction and during operation of anoffshore windfarm.BSH published a standardised guidance ‘Offshorewindfarms: Measuring instruction for underwatersound monitoring’ in October 2011(BSH 2011). Based on initial results from acousticinvestigations at the alpha ventus test site (seeabove in this chapter) and offshore researchplatforms, the instruction gives detailed informationon performing and analysing acousticmeasurements. It became the legal basis forconducting investigations of underwater noiseat offshore windfarms and supplements theStUK4. The instruction describes the generalprocedure for measuring underwater soundconnected with the construction and operationof offshore windfarms. It covers the four licensingand enforcement phases for offshore installationsin the German EEZ:a) Baseline study/ preliminary investigationsb) Construction phasec) Operation phased) Decommissioning phaseThe institutions in charge of carrying out soundmeasurements must provide an accreditationaccording to DIN EN ISO/IEC 17025 or equivalent.The required certification must be presentedon request to BSH.Detailed information on the BSH measuring instructionis provided on ▶ www.bsh.de.LiteratureBSH (2013). Standard Investigation of the Impacts of OffshoreWind Turbines on the Marine Environment (StUK4).Bundesamt für Seeschifffahrt und Hydrographie, Hamburgand Rostock, 86 p.BSH (2011). Offshore wind farms: Measuring instruction for underwatersound monitoring, Current approach with annotations.Bundesamt für Seeschifffahrt und Hydrographie,Hamburg and Rostock, 31 p.Betke, K (2012). Underwater construction and operational noiseat alpha ventus. RAVE (Research At alpha ventus) InternationalConference, May 8–10, 2012.Betke K & Matuschek M (2012). Messungen von Unterwasserschallbeim Betrieb der Windenergieanlagen im Offshore-Windpark alpha ventus. Oldenburg, May 2012 (report onbehalf of the Federal Ministry for the Environment, NatureConservation and Nuclear Safety (BMU) and Stiftung Offshore-Windenergie.