The demand for renewable energy has led to construction of offshore wind farms with high-power turbines, and many more wind farms are being planned for the shallow waters of the world's marine habitats. The growth of offshore wind farms has raised concerns about their impact on the marine environment. Marine mammals use sound for foraging, orientation and communication and are therefore possibly susceptible to negative effects of man-made noise generated from con- structing and operating large offshore wind turbines. This paper reviews the existing literature and assesses zones of impact from different noise-generating activities in conjunction with wind farms on 4 representative shallow-water species of marine mammals. Construction involves many types of activities that can generate high sound pressure levels, and pile-driving seems to be the noisiest of all. Both the literature and modeling show that pile-driving and other activities that generate intense impulses during construction are likely to disrupt the behavior of marine mammals at ranges of many kilometers, and that these activities have the potential to induce hearing impairment at close range. The reported noise levels from operating wind turbines are low, and are unlikely to impair hearing in marine mammals. The impact zones for marine mammals from operating wind turbines depend on the low-frequency hearing-abilities of the species in question, on sound-propagation conditions, and on the presence of other noise sources such as shipping. The noise impact on marine mammals is more severe during the construction of wind farms than during their operation.

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Wind turbine underwater noise and marine mammals: implications of current knowledge and data needs

An overview is given of the July-August 1995 SWARM shallow-water internal wave acoustic scattering experiment. This experiment studied both acoustic propagation through and scattering by the linear and nonlinear internal waves found on the Mid-Atlantic Bight continental shelf, as well as the physical oceanography of the internal wavefield. In order that their goal of explaining the nature of the acoustic scattering should not be hindered by incomplete environmental knowledge, numerous instruments, both ship-deployed and moored, measured the acoustics, geophysics, and oceanography. In this paper, the authors show some of the results from the first year's analysis of the environmental and acoustic data. The environmental measurements, which are a key input to the analyses of the acoustic data, are given slightly more emphasis at this point in time. Some of the more interesting oceanographic, geophysical, and acoustical results the authors present are: evidence for the dominance of the lee-wave mechanism for soliton production, evidence for the "solibore internal tide" the "dnoidal wave" description of solitons, the inversion of chirp sonar data for bottom properties, propagation loss extraction from air-gun data, and the intensity and travel-time fluctuations seen in propagating acoustic normal modes. Directions for future research are outlined.

An overview of the 1995 SWARM shallow-water internal wave acoustic scattering experiment

Translated from the official German naval history of the First World War, this account is based upon the war diaries of the commanding officers involved and makes extensive use of the texts of naval staff memoranda andinstructions, operation and war orders, and German wireless messages. Concentrating on the North Sea area, the volume begins with an examination of the background of the conflict and the preliminary German preparations for the warvis-a-vis those of the British Navy, and then proceeds to the early operations of the two fleets during August 1914. The detailed treatment reflects theimportance of this initial stage of the contest, in which are exhibited the maritime planning and determinations that set the course of the entire naval conduct of the war: the blockade by Britain and the German employment of the submarine and mine warfare. Relevant appendices, tables, and charts accompany each part. English translation of Der krieg in der Nordsee ________. The War in the North Sea. Volume I. From the Beginning of the War to the First of September, 1914. Part 2. Chapters 5,6; Appendices 14-21; Charts 1835. Newport, RI: Naval War College, 1937. (ADA003032). 220 p. English translation of Der krieg in der Nordsee. Halpern, Paul G. A naval history of World War I. Annapolis, MD: Naval Institute Press, c1994. 591 p. NPS/DKL Location: RESERVE D580 .H34 1994 Hoehling, Adolph A. The Great War at sea: a history of naval action, 1914-1918. Crowell, [1965]. 336 p. NPS/DKL Location: GENERAL D580 .H6 ________. The Great War at sea: a history of naval action 1914-18. New York: Galahad Books, [1975] c1965. 336 p. Originally published: New York, Crowell, 1965. ________. The Great War at sea: a history of naval action, 1914-18. Westport, CT: Greenwood Press, 1978, c1965. 336 p. Reprint of the edition published by Crowell, New York, 1965. Newbolt, Henry John, Sir. A naval history of the war. London, Hodder & Stoughton limited, [1920]. 350 p. Plaschka, Richard Georg. Matrosen, Offiziere, Rebellen: Krisenkonfrontationen zur See, 1900-1918: Taku, Tsushima, Coronel/Falkland, "Potemkin," Wilhelmshaven, Cattaro. Wien: H. Bohlau, 1984. (Veroffentlichungen des Osterreichischen Ostund Sudosteuropa-Instituts; Bd. 12-13). 2 v. Reynolds, Francis Joseph et al, ed. The story of the Great War. New York, P.F. Collier & son, [c1916-1920]. 16 v. NPS/DKL Location: BUCKLEY D521 .R4

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Submarine Warfare in the 20 th & 21 st Centuries: A Bibliography

Underwater noise modelling for environmental impact assessment

During August 1992, a combined acoustics/physical oceanography experiment was performed to study both the acoustical properties and the ocean dynamics of the Barents Sea Polar Front in the region near Bear Island. Oceanographic observations from shipboard hydrography and moored sensors allowed the construction of the internal wave frequency spectrum for the area. A rapidly sampled tomographic section from a 224‐Hz, 16‐Hz‐bandwidth acoustic source to a 16‐element vertical receiving array enabled the monitoring of travel‐time fluctuations over the internal wave frequency band. To describe the measured acoustic fluctuations, theoretical expressions have been developed for the travel‐time variances which are functions of the internal wave oceanographic field, the local acoustic propagation characteristics, and the acoustical system’s properties. Both ray and mode theory expressions are generated, as the experiment was performed in shallow water and both ray and mode arrivals were resolvable. Comparison of the...

http://oce.uri.edu/facultypages/miller/Lynchetal1996.pdf

Acoustic travel-time perturbations due to shallow-water internal waves and internal tides in the Barents Sea Polar Front: Theory and experiment

Fundamentals of Shallow Water Acoustics

shallowand deep-water acoustics. But during the cold war, the research emphasis shifted abruptly to deep water, where the ballistic missile submarine threat lurked (see box 1). After the cold war, the onset of regional conflicts in coastal countries shifted the focus again to shallow water. Those waters encompass about 5% of the world’s oceans on the continental shelves, roughly the region from the beach to the shelf break, where water depths are about 200 meters. To a significant extent, the problems of shallow-water acoustics are the same as those encountered in nondestructive testing, medical ultrasonics, multichannel communications, seismic processing, adaptive optics, and radio astronomy. In these fields, propagating waves carry information, embedded within some sort of noise, to the boundaries of a minimally accessible, poorly known, complex medium, where it is detected.1,2 Although submarine detection has driven much of the acoustics research, other important applications have emerged, such as undersea communications, mapping of the ocean’s structure and topography, locating mines or archaeological artifacts, and the study of ocean biology. Shallow water is usually a noisy environment because shipping lanes exist along coastlines. Submarines typically radiate in the same frequency band as shipping noise, less than 1 kilohertz. The proliferation of quiet submarine technology has restimulated the development of active sonar systems, which send out pulses and examine their echoes, rather than the more stealthy, passive approach of listening and exploiting the relevant physics. However, the ultimate limits of passive acoustics in terms of signal-tonoise ratio (SNR), acoustic aperture (or antenna) size, and the ocean environment are ongoing research issues. The sound speed in water is about 1500 m/s, so wavelengths of interest are on the order of a few meters. In shallow water, with boundaries framed by the surface and bottom, the typical depth-to-wavelength ratio is about 10–100. That ratio makes the propagation of acoustic waves there analogous to electromagnetic propagation in a dielectric waveguide. But the shallow ocean is an exceedingly complicated place. The surface and the ocean’s index of refraction have a spatial and time dependence, and the presence of ocean inhomogeneities and loud ships can frequently scatter, jam, or mask the most interesting sounds. So, whether using active or passive techniques, scientists are ultimately concerned with the physics of extracting a signal that propagates in a lossy, dynamic waveguide from noise influenced by that same waveguide’s complexity. In that light, and considering our still imperfect understanding of coastal oceanography, one can begin to appreciate shallow-water acoustics as an interdisciplinary blend of physics, signal processing, physical oceanography, marine geophysics, and even marine biology.

Shallow Water Acoustics

We investigated the specific features low-frequency (50–300 Hz) sound propagation in shallow-water areas to relatively small distances r ≈ 3H–50H from the sound source, where H is the waveguide depth. The bottoms of water areas were assumed to be fluid homogeneous gas-containing media. Situations were compared in which the sound velocity in the bottom is higher and lower than in the water layer (hard and soft bottom). It was confirmed in experiment that the average effective sound velocity in the bottom may have rather low values (≈100 m/s). The mode description of the acoustic field was used in calculations, and both propagating and outgoing modes, including quasi-modes, were taken into account. The averaged dependences of the field intensity decay on distance were obtained for different frequencies and sound velocities in the bottom. The sound damping factors β in the waveguide were found as functions of frequency and sound velocity in the bottom. It is shown that for a soft bottom, the value of β monotonically increases with an increase in the sound velocity in the bottom, while for a hard bottom, β monotonically decreases. The maximum of β depends on the sound frequency and is reached at the approximate equality of the sound velocities in the bottom and water.

Attenuation of sound in shallow-water areas with gas-saturated bottoms

The space-time spectral characteristics of the field of background internal waves (IW) are obtained for two oceanic shelf regions (the Atlantic shelf of the United States and the Kamchatka shelf) and analyzed. Within the framework of a numerical experiment, it is shown that the observed anisotropy of the IW field may considerably affect the low-frequency sound fluctuations in the aforementioned regions and, in particular, may change the interference invariant of the sound field.

Anisotropic field of background internal waves on a sea shelf and its effect on low-frequency sound propagation

Considerable shifts Δf/ϕ ≈ 10−1 of the low-frequency sound field interference pattern in the frequency domain, associated with barotropic tide and internal tidal waves, were observed in the Shallow Water’06 experiment on the New Jersey shelf in the summer of 2006. The acoustic frequency shifts appear to be strongly dependent on the modes of the sound field. By examining different modal structure, it is possible to analyze the overall interference pattern and find which part is more sensitive either to the surface tide or the internal waves. This feature can be exploited to acoustically monitor tidal waves of different kinds.

Valery Petnikov

Papers

Fundamentals of Shallow Water Acoustics

Shallow Water Acoustics

Attenuation of sound in shallow-water areas with gas-saturated bottoms

Anisotropic field of background internal waves on a sea shelf and its effect on low-frequency sound propagation

Frequency shifts of the sound field interference pattern on oceanic shelf in summer conditions