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.

The University of Rhode Island recently completed an assessment of the potential acoustic and other effects of the wind farms on the ecosystem. A developer has proposed to initially construct eight 3.6-MW wind turbines on lattice jacket structures 5 km south of Block Island and approximately 100 turbines in a second stage 20 km east of Block Island. Construction on the first stage is tentatively planned for summer of 2011, and pile driving will be the main source of noise. The main source of operational noise will likely be vibration from the turbine conducted through the lattice jacket structure into the water. Two passive aquatic listener (PAL) systems were deployed 5 km of Block Island from October 6 to November 11, 2008. Two more PAL systems were deployed on meteorological buoys, one near the first farm and one near the larger farm, for 12 months in 2009/2010. Using data from the PALs, ambient noise budgets and histograms were computed for this pre-construction phase. The largest sources of noise were found to be shipping, wind, rain, and biological sources. An assessment of the effects of the offshore wind farms will be presented for both the construction and operational phases.