摘要 :
Seabed geoacoustic structure exhibits variability on a wide spectrum of spatial scales. An experiment was designed and conducted (under the TREX13 experiment) to measure those scales in an inner shelf ridge and swale environment o...
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Seabed geoacoustic structure exhibits variability on a wide spectrum of spatial scales. An experiment was designed and conducted (under the TREX13 experiment) to measure those scales in an inner shelf ridge and swale environment off the coast of Panama City, Florida. One of the surprising results was the observation that significant scales of lateral variability in the sub-bottom exist at scales of 1-10 m. This was observed at both measurement sites, one on a small ridge and one in a swale. Very large differences were observed between the gross sediment properties on the ridge and in the swale despite there being only 30 cm difference in water depth between them. Some of the physical properties could be estimated, but many of the geoacoustic results are rather qualitative. New techniques are required for fully quantifying the geoacoustic variability in such a heterogeneous environment.
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Results of a 5-year program to measure the seismoacoustic properties ofunlithified sediments in the seafloor are presented. A field technique utilizing an impulsive source and a geophone array located on the seafloor was used to o...
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Results of a 5-year program to measure the seismoacoustic properties ofunlithified sediments in the seafloor are presented. A field technique utilizing an impulsive source and a geophone array located on the seafloor was used to obtain detailed travel-time curves which permit a number of different kinds of analysis. A new signal source powered by electrically detonated, 8-gauge shotgun shells was used to focus energy into the bottom and eliminate much of the high-frequency water-borne noise that accompanies the usual explosive sources. Both interface waves and wide-angle refractions were analyzed. A variety of data inversion techniques including slant stacking and cross multiplication were used to obtain dispersion curves, and constrained, least-squares inversion using partial derivatives was used to develop an iterative inversion method to obtain velocity and attenuation as a function of depth. Examples of data from a wide range of different kinds of sediment ranging from soft Holocene mud to stiff overconsolidated clay are presented.
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摘要 :
Our long-term objective is to develop an inversion scheme for the estimation of acoustic properties of sediments in shallow water at long range using broadband explosive sources.
摘要 :
An acoustic subbottom profiling study has been performed along the center line ofthe Delaware River Main Channel from the Ben Franklin Bridge in Philadelphia, PA, to the entrance of the ship channel near the east end of Delaware B...
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An acoustic subbottom profiling study has been performed along the center line ofthe Delaware River Main Channel from the Ben Franklin Bridge in Philadelphia, PA, to the entrance of the ship channel near the east end of Delaware Bay for the purpose of identifying sediment units within areas scheduled for dredging. The study is focused on deepening of the Delaware River Main Channel from 40 to 45 ft. The specific objective was to quantify the bottom and subbottom sediments in terms of in situ density and soil type to a depth of about 20 ft, where possible, below the bottom of the existing ship channel. Data from 29 vibracores collected
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摘要 :
The long-term scientific objective of this research is to develop a geoacoustic model of the seafloor using laboratory studies for better understanding the physics of interaction between sound and marine sediments. The emphasis is...
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The long-term scientific objective of this research is to develop a geoacoustic model of the seafloor using laboratory studies for better understanding the physics of interaction between sound and marine sediments. The emphasis is on phenomena encountered in the interaction of high-frequency acoustic signals with littoral ocean bottoms.
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摘要 :
The shear modulus of a sediment is directly related to shear wave velocity, and essential geoacoustic parameter not easily measured in the laboratory. Further, both shear modulus and shear wave velocity are a function of the effec...
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The shear modulus of a sediment is directly related to shear wave velocity, and essential geoacoustic parameter not easily measured in the laboratory. Further, both shear modulus and shear wave velocity are a function of the effective stress on a sediment. The objective of this research is to develop a simple laboratory test procedure to measure the shear modulus of a sediment under controlled loading conditions. To do this, a Duomorph has been constructed similar to ones designed by Briar at al. (1). Compressional wave velocity has been measured using the NORDA compressional wave transducers before and after consolidation to validate the duomorph results. Initial results indicate that the concept is feasible and continued testing is planned. Duomorph, Shear modulus, Geotechnical properties, Reprints. (mjm)
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摘要 :
Our work focuses on understanding the frequency and depth dependence of compressional wave attenuation and developing new inversion schemes for shear wave properties. Our initial investigations have indicated that water-borne acou...
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Our work focuses on understanding the frequency and depth dependence of compressional wave attenuation and developing new inversion schemes for shear wave properties. Our initial investigations have indicated that water-borne acoustic arrival properties such as their Airy Phase are sensitive to sediment shear properties. Our major emphasis this year has been to develop and test inversion schemes for simultaneous estimation of compressional and shear properties. The long term goals of our research are to: * Improve inversion schemes for the estimation of sediment geoacoustic properties using low frequency broadband acoustic signals at short and long ranges. * Continue fine-tuning our Shear Measurement System, recently developed under a DURIP grant, for short range interface/Scholte wave-based inversions for shear properties. * Adapt our long range sediment tomography technique for compressional and shear wave speeds, and attenuation profiles utilizing the broadband Combustive Sound Source (CSS) developed at the Applied Research Laboratories (ARL), University of Texas.
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