Horizontal refraction and diffraction of underwater sound around an island.

The three-dimensional (3D) propagation effects of horizontal refraction and diffraction were measured on a tetrahedral hydrophone array deployed near the coast of Block Island, RI. Linear frequency modulated chirp signals, centered at 1 kHz with a 400 Hz bandwidth, were transmitted from a ship moving out of the acoustic shadow zone blocked by the island from the perspective of the hydrophone array. The observed shadow zone boundary was consistent with the prediction made by a 3D sound propagation model incorporating high-resolution bathymetry and realistic sound speed obtained from a data-assimilated regional ocean model. The 3D modal ray calculation provided additional insight into the frequency dependence of the signal spreading. This analysis found that the modes at higher frequencies can propagate closer to the coast of the island with shallower modal cutoff depths, where the sound energy penetrates the sloping seafloor at supercritical incidence. The evidence of horizontal caustics of the sound was shown in the parabolic equation and modal ray models by comparing to the arrival pattern observed in the data. The arrival angle measurements on the tetrahedral array show the complex propagation patterns, including the diffracted energy in the island shadow and acoustic energy refracted away from the island.

Characterization of impact pile driving signals during installation of offshore wind turbine foundations.

Impact pile driving creates intense, impulsive sound that radiates into the surrounding environment. Piles driven vertically into the seabed generate an azimuthally symmetric underwater sound field whereas piles driven on an angle will generate an azimuthally dependent sound field. Measurements were made during pile driving of raked piles to secure jacket foundation structures to the seabed in waters off the northeastern coast of the U.S. at ranges between 500 m and 15 km. These measurements were analyzed to investigate variations in rise time, decay time, pulse duration, kurtosis, and sound received levels as a function of range and azimuth. Variations in the radiated sound field along opposing azimuths resulted in differences in measured sound exposure levels of up to 10 dB and greater due to the pile rake as the sound propagated in range. The raked pile configuration was modeled using an equivalent axisymmetric FEM model to describe the azimuthally dependent measured sound fields. Comparable sound level differences in the model results confirmed that the azimuthal discrepancy observed in the measured data was due to the inclination of the pile being driven relative to the receiver.

A three-dimensional underwater sound propagation model for offshore wind farm noise prediction.

A three-dimensional underwater sound propagation model with realistic ocean environmental conditions has been created for assessing the impacts of noise from offshore wind farm construction and operation. This model utilizes an existing accurate numerical solution scheme to solve the three-dimensional Helmholtz wave equation, and it is compared and validated with acoustic transmission data between 750 and 1250 Hz collected during the development of the Block Island Wind Farm (BIWF), Rhode Island. The variability of underwater sound propagation conditions has been investigated in the BIWF area on a temporal scale of months and a spatial scale of kilometers. This study suggests that future offshore wind farm developments can exploit the seasonal variability of underwater sound propagation for mitigating noise impact by scheduling wind farm construction during periods of high acoustic transmission loss. Discussions on other applications of soundscape prediction, planning, and management are provided.

Stochastic Modeling of Behavioral Response to Anthropogenic Sounds.

The effect of anthropogenic sounds on marine wildlife is typically assessed by convolving the spatial, temporal, and spectral properties of a modeled sound field with a representation of animal distribution within the field. Both components benefit from stochastic modeling techniques based on field observations. Recent studies have also highlighted the effect of context on the probability and severity of the animal behavioral response to sound. This paper extends the stochastic approach to three modeling scenarios, including key contextual variables in aversion from a given level of sound and as a means of evaluating the effectiveness of passive acoustic monitoring.

Discovery of Sound in the Sea: Resources for Educators, Students, the Public, and Policymakers.

There is increasing concern about the effects of underwater sound on marine life. However, the science of sound is challenging. The Discovery of Sound in the Sea (DOSITS) Web site ( http://www.dosits.org ) was designed to provide comprehensive scientific information on underwater sound for the public and educational and media professionals. It covers the physical science of underwater sound and its use by people and marine animals for a range of tasks. Celebrating 10 years of online resources, DOSITS continues to develop new material and improvements, providing the best resource for the most up-to-date information on underwater sound and its potential effects.