The project’s goal was to provide a statistical description of ambient sound levels for one year at two locations likely to be developed for offshore wind-energy production. The chosen sites were offshore Delaware Bay and Nantucket Sound. The preconstruction description of ambient sound levels provides a baseline that can later be used for comparisons, such as during construction, operation, and maintenance of the wind farms. These baseline descriptions can also be used for comparison with other sites. The statistical description of ambient sounds levels was presented as percentile spectral-level histograms of the spectral density values. As a measure of relative overall sound levels and as an indication of possible sources of sound, the percentile levels were compared with the envelope values of the Wenz curves (Wenz 1962). In general, the Wenz curves are reasonable predictors of the ambient noise levels at the two locations; however, there are frequency bands and seasons when sound levels are greater than those predicted by the Wenz curves.
Both manual and automated detection and classification were performed on the recordings to identify prominent sources of sound. Anthropogenic sources, such as heavy shipping, were found at each site throughout the year and could exceed the maximal predictions of the Wenz curves. Large storms, including hurricanes and Nor’easters, produce rain and wind with high waves and are natural sources of sound.
Biological sound activity included marine mammal and fish sounds. Delphinids (likely bottlenose dolphins (Tursiops truncatus) and some unidentified species) and fin whales (Balaenoptera physalus) were the most commonly detected marine mammals at offshore Delaware Bay. North Atlantic right whale (Eubalaena glacialis) calls were detected on a few occasions at both sites. Humpback whale (Megaptera novaeangliae) call detections occurred only at the offshore Delaware Bay site. Fish choruses were heard in late summer and fall at offshore Delaware Bay and in winter and summer at Nantucket Sound. These events occasionally exceeded the Wenz curves.
Ambient sound levels differ throughout the year at each site and between each site, but the differences are largely attributable to identifiable events and sources.