Proceedings of the 3rd Underwater Acoustic Measurement: Technology and Results Conference
Marine piling is the most commonly-used method for offshore windfarm construction, and consists of steel monopiles being driven into the sea-bed using powerful hydraulic hammers. This is a source of high-level impulsive sound that can travel considerable distance in the water column. This paper describes a methodology that has been developed for measuring marine piling noise, which is designed to record the temporal, spatial and spectral characteristics of the radiated sound field. In the method, a number of recording systems are simultaneously deployed at various ranges and depths. Fixed recording buoys allow the full piling sequence to be measured, and variations in the temporal and spectral characteristics to be assessed. This enables the effect of any source level variation with time to be determined, for example that due to a soft start procedure. To assess spatial variations in the radiated acoustic field, recording samples are also made using hydrophones deployed from a vessel which traverses the field along a radial transect from the pile location. This latter set of measurements allows an estimate of the effective source level to be made if a suitable transmission loss model is used. To illustrate the method, some results are presented of measurements made on marine piling in shallow coastal waters during the construction phase of offshore windfarms.
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