On the use of noise budgets to assess the effects of offshore wind farms on marine life.

Abstract

An ocean noise budget is a list of sources of noise along with their average intensity in a particular frequency band [Frisk et al. (2003)]. The budget can be calculated from acoustic data collected by the passive aquatic listener (PAL) systems [Nystuen and Howe (2005); Miller et al. (2008)]. In the far field, the average acoustic intensity of plane waves can be computed in 1/3-octave bands over some duration. The assumption is made that the noise in the band at any one time is dominated by a single, identifiable source such as wind, rain, shipping, fish, marine mammals, etc. The duration and instantaneous intensity of the acoustic signal is used to calculate the average. Identification is carried out using the ratios of various spectral levels as outlined in the work of Ma et al. [(2005)]. We apply the concept of noise budgets to the assessment of the impact of long term noise from offshore wind turbines on marine life. A developer has proposed to construct more than 200 wind turbines south of Rhode Island. A noise budget has been calculated for the region from data collected on PALs. The addition of the 200 turbines will be incorporated into the budget parametrized on source level.