Ocean Noise and Marine Mammals (2003) / Chapter Skim
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4. Modeling and Databases of Noise in the Marine Environment
4. Modeling and Databases of Noise in the Marine Environment
Pages 109-126
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From page 109... ...
ACOUSTIC MODELING OF THE MARINE ENVIRONMENT Noise in the ocean is usually broken into two broad categories based on the type of source. The first type of noise is generated by a single, identifiable, and usually close source of noise, such as an air-gun array or one or more marine mammals or other biological sources.
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From page 110... ...
Models are used to assess the interactions of sound fields created by multiple sources, propagation through space and time, and interactions with marine mammals. The term "models" refers to a variety of tools, including empirical fits to measured data, such as the Wenz curves, computer simulation models, and numerical models, which can be either physics or empirical based.
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From page 111... ...
Each of these different categories represents a different approach to simplifying either the acoustic wave equation (the fundamental mathematical equation that contains all the basic physics of sound propagation) or the mode!
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From page 114... ...
114 o :~ 0 o O 0 Q to ~ to ~ to O o C Cp o o o o o o o Cal Cal o o o o o o o o ~ o ~ o C" ~ ~ ~ o ·_ Ct ·_ .= Ct ~ U
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From page 115... ...
. Below 10 Hz, microseisms caused by the nonlinear interaction of ocean surface waves are the dominant source of ocean noise.
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From page 116... ...
, , , ~ , ~ The initial attempts to define and measure noise directionality were confined to studies of the variations either in the vertical direction only or the azimuthal direction only. Later, as the sonar arrays became even more spatially discriminating, beam noise estimates were required where both horizontal and vertical limits were used.
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From page 117... ...
is capable of predicting the effects of distributed noise sources on marine mammals. An omnidirectional ambient noise mode!
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From page 118... ...
The ocean noise input to the system of marine mammals consists of all types of ocean noise, including those generated naturally by physical and biological means and those generated from human activities (Chapter 2~. The system being evaluated consists of marine mammals and in the simplest terms can be treated as multiple environmental and physical factors on which the ocean acts to produce the output.
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From page 119... ...
of effects that predicts the impact of acoustic signals on marine mammals should consist of six main components: (1) a description of
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From page 120... ...
physical oceanographic and geoacoustic databases, (3) models of marine mammals distribution in three dimensions to determine exposure, (4)
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From page 121... ...
in order to modify the inner ear response models to accurately represent stiffness and mass variations in marine mammals compared to smaller land mammals. This will affect both sensitivity and frequency responses in marine ears.
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From page 122... ...
Another program, the Living Marine Resources Information System, is developing databases of global distributions of marine animal species with no acoustic data. The primary sources of information presently are the National Marine Fisheries Service visual survey reports, as well as other publications in the open literature; however these data are confined largely to coastal areas.
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From page 123... ...
Lloyds of London maintains information about the merchant fleets of the world, the number of ships in each ship-type category, and gross tonnage. Oil industry activity that contributes most to ocean noise can be monitored by subscribing to any of a number of commercial information services.
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From page 124... ...
It is beyond the scope of this report to discuss this topic here other than to say that in some instances it is crucial to know the details of the seafloor topography, the details of the water column sound speed and absorption properties, and the details of the seismic velocities, densities, and absorption properties of the strata below the seafloor. Although there is an extensive literature on the effects of sound on marine mammals, it is patchy and inconclusive.
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From page 125... ...
Etter's Table 10.3 lists the Advanced Environmental Acoustic Support data bank as well as the NAVOCEANO database, and Table 10.5 contains noise databases that reside in the OAML. These OAML-approved databases include three shipping noise databases that cover all of the northern hemisphere as a function of season, Arctic noise near the marginal ice zone on a monthly basis, and the wind and residual noise database, which provides monthly variations in noise levels not containing shipping for the northern hemisphere.
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From page 126... ...
Development of a long-term ocean noise monitoring system requires careful consideration of which types and in what ways this supporting information will be collected. SUMMARY Sound sources in the ocean can be categorized and modeled as two main types: unknown distributed sources (that is, unknown location, source level, and spectral content)
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