The Marine Seismic Source

Parkes, Gregg; Hatton, Les

doi:10.1007/978-94-017-3385-4

Cited by 45 publications

(26 citation statements)

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“…Imploders generate the signal by the collapse of a volume, created for instance by cavitation. We can further distinguish between chemical, mechanical, electrical, and pneumatic/hydraulic sources (Parkes and Hatton, 1986). Chemical sources comprise various explosives.…”

Section: Seismic Energy Sourcesmentioning

confidence: 99%

Reflection/Refraction Seismology

Hübscher

Gohl

2014

Encyclopedia of Marine Geosciences

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SynonymsControlled-source seismology; Multichannel reflection seismics; Wide-angle reflection/refraction profiling (WARRP) DefinitionsMethods to image and to physically parameterize the subsurface geologic structures and conditions by means of artificially generated shock waves that travel through the subsurface and return to the surface. OverviewControlled-source seismology comprises a variety of geophysical methods to image and to physically parameterize the subsurface geologic structures and conditions. All these methods base upon the principle that artificially generated shock waves travel through the subsurface and that the returned signal can be analyzed regarding the properties of the subsurface. During the last decades the discrepancies between marine seismic equipment as used by the academic marine research community and that used by the hydrocarbon (HC) exploration industry increased significantly, caused by different research targets and the simple fact that gear commonly used for HC exploration is much too costly. In this chapter we will focus on those systems which are typical for academic marine research.In principle, seismic data acquisition requires an energy source, a receiver, and a recording system. The two most important seismic methods are reflection and refraction seismology (Fig. 1).Reflection seismologists deal mainly with steep angle reflections, which means that the source to receiver distance is small compared to the target depth. This method utilizes the fact that a small part of the down-going energy is reflected on geological layer boundaries. The main fraction of the energy is transmitted and travels deeper where reflections occur at the next layer boundary and so on. This method results in a good vertical and horizontal structural resolution of the subsurface. Earth scientists benefit from the technical and methodical developments of the exploration industry which uses reflection seismology for the detection of oil and gas in depths of up to several kilometers below the seafloor.

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Section: Seismic Energy Sourcesmentioning

confidence: 99%

Reflection/Refraction Seismology

Hübscher

Gohl

2014

Encyclopedia of Marine Geosciences

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“…Airguns generate sound by rapidly releasing compressed air from an airgun cylinder, creating an oscillating air bubble that acts as a source of loud, broadband impulsive sound. The oscillating air bubble also produces a sequence of exponentially decaying bubble pulses following the initial pulse (Parkes and Hatton, 1986). Airguns are generally deployed as horizontal planar towed arrays, minimizing the bubble pulses and directing the main beam of low-frequency sound toward the seafloor (Parkes and Hatton, 1986).…”

Section: Modeling Acoustic Propagation Of Airgun Array Pulses Recordementioning

confidence: 99%

“…The oscillating air bubble also produces a sequence of exponentially decaying bubble pulses following the initial pulse (Parkes and Hatton, 1986). Airguns are generally deployed as horizontal planar towed arrays, minimizing the bubble pulses and directing the main beam of low-frequency sound toward the seafloor (Parkes and Hatton, 1986). Airgun arrays are reported to have theoretical on-axis (directly downward) signatures with peak energy in the 10-200 Hz range, and far-field measure- Pages: 4100-4114 ments yield typical peak-to-peak source levels in the range 222-261 dB re 1 ,Pa when corrected to a source range of 1 m, treating the full array as a point source .…”

Section: Modeling Acoustic Propagation Of Airgun Array Pulses Recordementioning

confidence: 99%

“…This reflected arrival is equivalent to the sound that would be received from a virtual mirror image source located above the sea surface, with approximately the same source amplitude as the airgun array but with opposite polarity [the exact mirror source amplitude depends on sea-surface roughness and source frequency (Jovanovich et al, 1983)]. Interference between the direct pulse and the surface reflection affects the time and frequency structure of pulses recorded at distant receivers, lengthening the pulse and introducing frequency nulls into the source spectrum Parkes and Hatton, 1986). The effect varies with airgun array tow depth: as tow depth increases, frequency nulls occur at more closely spaced intervals in the source spectrum, and source pressure amplitude increases at frequencies below 100 Hz (Parkes and Hatton, 1986).…”

Section: A Sound Sources: Airgun Arraysmentioning

confidence: 99%

“…Interference between the direct pulse and the surface reflection affects the time and frequency structure of pulses recorded at distant receivers, lengthening the pulse and introducing frequency nulls into the source spectrum Parkes and Hatton, 1986). The effect varies with airgun array tow depth: as tow depth increases, frequency nulls occur at more closely spaced intervals in the source spectrum, and source pressure amplitude increases at frequencies below 100 Hz (Parkes and Hatton, 1986). The beampattern of a planar array composed of identical point sources has grating lobes when the spacing between array elements, d, is greater than X/2 (where h is source wavelength).…”

Section: A Sound Sources: Airgun Arraysmentioning

confidence: 99%

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Echolocation-based foraging by harbor porpoises and sperm whales, including effects of noise and acoustic propagation

DeRuiter¹

2008

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In this thesis, I provide quantitative descriptions of toothed whale echolocation and foraging behavior, including assessment of the effects of noise on foraging behavior and the potential influence of ocean acoustic propagation conditions on biosonar detection ranges and whale noise exposure. In addition to presenting some novel basic science findings, the case studies presented in this thesis have implications for future work and for management.In Chapter 2, I describe the application of a modified version of the Dtag to studies of harbor porpoise echolocation behavior. The study results indicate how porpoises vary the rate and level of their echolocation clicks during prey capture events; detail the differences in echolocation behavior between different animals and in response to differences in prey fish; and show that, unlike bats, porpoises continue their echolocation buzz after the moment of prey capture.Chapters 3-4 provide case studies that emphasize the importance of applying realistic models of ocean acoustic propagation in marine mammal studies. These chapters illustrate that, although using geometric spreading approximations to predict communication/target detection ranges or noise exposure levels is appropriate in some cases, it can result in large errors in other cases, particularly in situations where refraction in the water column or multi-path acoustic propagation are significant.Finally, in Chapter 5, I describe two methods for statistical analysis of whale behavior data, the rotation test and a semi-Markov chain model. I apply those methods to test for changes in sperm whale foraging behavior in response to airgun noise exposure. Test results indicate that, despite the low-level exposures experienced by the whales in the study, some (but not all) of them reduced their buzz production rates and altered other foraging behavior parameters in response to the airgun exposure. Sincere thanks also to the many other people who have helped with data collection and analysis over the course of my graduate work, and also to everyone who offered comments on drafts of this thesis. More detailed acknowledgments can be found at the end of each chapter, but here I would especially like to thank the following. Thesis Objectives and Chapter 1 OverviewThe goal of my thesis research has been to provide quantitative descriptions of toothed whale echolocation and foraging behavior (Chapters 2 and 5), including assessment of the effects of noise on foraging behavior (Chapter 5) and the potential influence of ocean acoustic propagation conditions on biosonar detection ranges (Chapter 3) and whale noise exposure (Chapter 4). I have focused on two study species, the harbor porpoise (Phocoena phocoena, Chapters 2-3) and the sperm whale (Physeter macrocephalus, Chapters 4-5).The following sections present background information relevant to the research presented in the rest of the thesis, beginning with a review of previous research on the use of echolocation by foraging animals. This review is followed by b...

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Petroleum production and its environmental impacts

Yuretich¹

Encyclopedia of Earth Science

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The Marine Seismic Source

Cited by 45 publications

References 0 publications

Reflection/Refraction Seismology

Reflection/Refraction Seismology

Echolocation-based foraging by harbor porpoises and sperm whales, including effects of noise and acoustic propagation

Petroleum production and its environmental impacts

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