Journal of the Acoustical Society of America, May 1, 2008
Grain roughness and packing may be important sediment properties for newer acoustic models. We pr... more Grain roughness and packing may be important sediment properties for newer acoustic models. We present Scanning Electron Stereomicroscopic imagery of natural sand grains of varying shape and roughness for evaluation of potential grain interactions of individual grains. The grain shape and presence of microasperities will determine the probability of the contact with surrounding grains being a point or a broader area. Moreover, the use of a micro-roughness power spectrum in characterizing the sand grain roughness may be appropriate. Grain contact information is an essential starting point for developing and evaluating acoustic models that address acoustic losses at high frequencies. This information provides the basis to understand contact mechanics, such as grain slip and frame dilation, during insonification. Because media frame stiffness depends, at the grain scale, on the number and type of grain-to-grain contacts, ultimately we would like to characterize sand sediments with imagery identifying such grain contact information. The natural shapes of grains, their variations, and their packing density present a variety of non-ideal (point) contacts. X-ray micro-focus Computed Tomography shows great promise for documenting of the number and size (area) of grain contacts within grain aggregations, and a demonstration of these data will also be presented.
The interaction of high-frequency sound with the seafloor is inherently a stochastic process. Inv... more The interaction of high-frequency sound with the seafloor is inherently a stochastic process. Inversion techniques must, therefore, employ good stochastic models for bottom acous- tic scattering. An assortment of physical models for bottom backscattering strength is tested by comparison with scattering strength data obtained at 40 kHz at three shallow water sites spanning a range of sediment types from fine silt to coarse sand. These acoustic data are accompanied by sediment physical property data obtained by core sample analysis and in situ probes. In addition, stereo photography was used to measure the power spectrum of bottom relief on centimeter scales. These physical data provided the inputs needed to test the backscatter models, which treat scattering from both the rough sediment-water in- terface and the sediment volume. For the three sites considered here, the perturbation model for scattering from a slightly rough fluid seafloor performs well. Volume scattering is predicted...
Abstract—Variation in the spatial and temporal extent of hypoxia in coastal bottom waters ofthe n... more Abstract—Variation in the spatial and temporal extent of hypoxia in coastal bottom waters ofthe northern Gulf of Mexico leads to changes in benthic community structure and sediment physical properties. Past and present benthic community structure determines what types of biogenic structures are present in the sediment as well as faunal mixing rates. Therefore, hypoxia has an important effect upon biorurbation. This study focuses upon the effects of hypoxia on biorurbation specifically on the continental shelf of Louisiana, where hypoxia has become an important issue due to its seasonal reoccurrence and increasing expansion across the northern Gulf of Mexico over the past 30 years. In this project, characteristics of biogenic structures in the sediment including number, diameter, and depth are correlated with benthic communities dwelling in hypoxic, intermittently hypoxic, and normoxic conditions using non-destructive Computed Tomography (CT) imagery of sediment cores and Sediment Pr...
The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection
: Our long-term goal is to improve sonar performance through interpretation of geological data an... more : Our long-term goal is to improve sonar performance through interpretation of geological data and high-frequency acoustic modeling. This work should improve understanding of the variability of the salient geoacoustic properties of the sea floor that control acoustic propagation and scattering.
The Pearson and Rosenberg (P-R) conceptual model of macrobenthic succession was used to assess th... more The Pearson and Rosenberg (P-R) conceptual model of macrobenthic succession was used to assess the impact of hypoxia (dissolved oxygen concentration ≤2 mg L–1) on the macrobenthic community on the continental shelf of the northern Gulf of Mexico. The stress-response relationship between bottom-water oxygen concentration and the macrobenthic community was used to determine the ecological condition of the benthic habitat. In lieu of testing the effect of decreasing influence of organic enrichment on the macrobenthic community as a function of distance from the source of organic pollution, we tested the effect of bottom-water dissolved oxygen concentration as a proxy for distance from the source. To include the seasonal response in the long-term cumulative effect of recurring hypoxia on the macrobenthic community, samples were collected during early spring (April 2009), late summer (September 2009), and midsummer (August 2010). The cumulative effect of annual hypoxia on the macrobenthos at each site was apparent from the species diversity, abundance, and biomass. High diversity values at site H7 and low diversity values at site A6 indicated the existence of a westward-diminishing hypoxic gradient on the Louisiana/Texas shelf, interrupted by the Atchafalaya River discharge. Unsurprisingly, the macrobenthos collected during midsummer were generally the most stressed community, with the exception of site E4. Assessment of successional stages of the benthic communities of the four sites with multivariate analyses of nonmetric multidimensional scaling, distance-based redundancy analysis, and principal component analysis identified the influence of bottom-water hypoxia. The study demonstrated the applicability of the P-R model in predicting successional change in the macrobenthic community on the Louisiana continental shelf. Site H7 was in the advanced phase of stage II, sites E4 and D5 were in the intermediate phase of stage II, and site A6 was in the intermediate phase of stage I in the P-R successional continuum
Physical and geoacoustic property data were collected during the Key West Campaign as a part of t... more Physical and geoacoustic property data were collected during the Key West Campaign as a part of the Coastal Benthic Boundary Layer research program.
: Long term goals are to (1) to develop/improve inversion techniques for normal incidence sedimen... more : Long term goals are to (1) to develop/improve inversion techniques for normal incidence sediment classification systems and remotely determine sediment physical and geoacoustic properties; (2) determine mechanisms responsible for scattering of high frequency energy.
Public reporting burden for this collection of information is estimated lo average 1 hour per res... more Public reporting burden for this collection of information is estimated lo average 1 hour per response, including the lime for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of
Journal of the Acoustical Society of America, 2017
Four sites on the continental shelf off Louisiana, each subjected to different historical exposur... more Four sites on the continental shelf off Louisiana, each subjected to different historical exposures to low concentrations of bottom-water dissolved oxygen, are investigated in terms of their macrobenthos species composition, sediment physical properties, and sediment geoacoustic properties (sound speed, attenuation, and impedance). From macrobenthos species composition, feeding type is identified, which allows categorization of some bioturbation activity as either dilation or compaction of sediment. Dilation and compaction should affect sediment properties of bulk density and porosity, which are significant predictor variables of geoacoustic properties. Different levels of oxygen stress correspond with statistically separable macrobenthos assemblages, abundance and diversity of biogenic structures (burrows and voids), and ratios of dilators to compactors. Sediment sound speed and attenuation values measured in subcores from box cores are compared at each of the four sites with diffe...
Journal of the Acoustical Society of America, May 1, 2008
Grain roughness and packing may be important sediment properties for newer acoustic models. We pr... more Grain roughness and packing may be important sediment properties for newer acoustic models. We present Scanning Electron Stereomicroscopic imagery of natural sand grains of varying shape and roughness for evaluation of potential grain interactions of individual grains. The grain shape and presence of microasperities will determine the probability of the contact with surrounding grains being a point or a broader area. Moreover, the use of a micro-roughness power spectrum in characterizing the sand grain roughness may be appropriate. Grain contact information is an essential starting point for developing and evaluating acoustic models that address acoustic losses at high frequencies. This information provides the basis to understand contact mechanics, such as grain slip and frame dilation, during insonification. Because media frame stiffness depends, at the grain scale, on the number and type of grain-to-grain contacts, ultimately we would like to characterize sand sediments with imagery identifying such grain contact information. The natural shapes of grains, their variations, and their packing density present a variety of non-ideal (point) contacts. X-ray micro-focus Computed Tomography shows great promise for documenting of the number and size (area) of grain contacts within grain aggregations, and a demonstration of these data will also be presented.
The interaction of high-frequency sound with the seafloor is inherently a stochastic process. Inv... more The interaction of high-frequency sound with the seafloor is inherently a stochastic process. Inversion techniques must, therefore, employ good stochastic models for bottom acous- tic scattering. An assortment of physical models for bottom backscattering strength is tested by comparison with scattering strength data obtained at 40 kHz at three shallow water sites spanning a range of sediment types from fine silt to coarse sand. These acoustic data are accompanied by sediment physical property data obtained by core sample analysis and in situ probes. In addition, stereo photography was used to measure the power spectrum of bottom relief on centimeter scales. These physical data provided the inputs needed to test the backscatter models, which treat scattering from both the rough sediment-water in- terface and the sediment volume. For the three sites considered here, the perturbation model for scattering from a slightly rough fluid seafloor performs well. Volume scattering is predicted...
Abstract—Variation in the spatial and temporal extent of hypoxia in coastal bottom waters ofthe n... more Abstract—Variation in the spatial and temporal extent of hypoxia in coastal bottom waters ofthe northern Gulf of Mexico leads to changes in benthic community structure and sediment physical properties. Past and present benthic community structure determines what types of biogenic structures are present in the sediment as well as faunal mixing rates. Therefore, hypoxia has an important effect upon biorurbation. This study focuses upon the effects of hypoxia on biorurbation specifically on the continental shelf of Louisiana, where hypoxia has become an important issue due to its seasonal reoccurrence and increasing expansion across the northern Gulf of Mexico over the past 30 years. In this project, characteristics of biogenic structures in the sediment including number, diameter, and depth are correlated with benthic communities dwelling in hypoxic, intermittently hypoxic, and normoxic conditions using non-destructive Computed Tomography (CT) imagery of sediment cores and Sediment Pr...
The public reporting burden for this collection of information is estimated to average 1 hour per... more The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection
: Our long-term goal is to improve sonar performance through interpretation of geological data an... more : Our long-term goal is to improve sonar performance through interpretation of geological data and high-frequency acoustic modeling. This work should improve understanding of the variability of the salient geoacoustic properties of the sea floor that control acoustic propagation and scattering.
The Pearson and Rosenberg (P-R) conceptual model of macrobenthic succession was used to assess th... more The Pearson and Rosenberg (P-R) conceptual model of macrobenthic succession was used to assess the impact of hypoxia (dissolved oxygen concentration ≤2 mg L–1) on the macrobenthic community on the continental shelf of the northern Gulf of Mexico. The stress-response relationship between bottom-water oxygen concentration and the macrobenthic community was used to determine the ecological condition of the benthic habitat. In lieu of testing the effect of decreasing influence of organic enrichment on the macrobenthic community as a function of distance from the source of organic pollution, we tested the effect of bottom-water dissolved oxygen concentration as a proxy for distance from the source. To include the seasonal response in the long-term cumulative effect of recurring hypoxia on the macrobenthic community, samples were collected during early spring (April 2009), late summer (September 2009), and midsummer (August 2010). The cumulative effect of annual hypoxia on the macrobenthos at each site was apparent from the species diversity, abundance, and biomass. High diversity values at site H7 and low diversity values at site A6 indicated the existence of a westward-diminishing hypoxic gradient on the Louisiana/Texas shelf, interrupted by the Atchafalaya River discharge. Unsurprisingly, the macrobenthos collected during midsummer were generally the most stressed community, with the exception of site E4. Assessment of successional stages of the benthic communities of the four sites with multivariate analyses of nonmetric multidimensional scaling, distance-based redundancy analysis, and principal component analysis identified the influence of bottom-water hypoxia. The study demonstrated the applicability of the P-R model in predicting successional change in the macrobenthic community on the Louisiana continental shelf. Site H7 was in the advanced phase of stage II, sites E4 and D5 were in the intermediate phase of stage II, and site A6 was in the intermediate phase of stage I in the P-R successional continuum
Physical and geoacoustic property data were collected during the Key West Campaign as a part of t... more Physical and geoacoustic property data were collected during the Key West Campaign as a part of the Coastal Benthic Boundary Layer research program.
: Long term goals are to (1) to develop/improve inversion techniques for normal incidence sedimen... more : Long term goals are to (1) to develop/improve inversion techniques for normal incidence sediment classification systems and remotely determine sediment physical and geoacoustic properties; (2) determine mechanisms responsible for scattering of high frequency energy.
Public reporting burden for this collection of information is estimated lo average 1 hour per res... more Public reporting burden for this collection of information is estimated lo average 1 hour per response, including the lime for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of
Journal of the Acoustical Society of America, 2017
Four sites on the continental shelf off Louisiana, each subjected to different historical exposur... more Four sites on the continental shelf off Louisiana, each subjected to different historical exposures to low concentrations of bottom-water dissolved oxygen, are investigated in terms of their macrobenthos species composition, sediment physical properties, and sediment geoacoustic properties (sound speed, attenuation, and impedance). From macrobenthos species composition, feeding type is identified, which allows categorization of some bioturbation activity as either dilation or compaction of sediment. Dilation and compaction should affect sediment properties of bulk density and porosity, which are significant predictor variables of geoacoustic properties. Different levels of oxygen stress correspond with statistically separable macrobenthos assemblages, abundance and diversity of biogenic structures (burrows and voids), and ratios of dilators to compactors. Sediment sound speed and attenuation values measured in subcores from box cores are compared at each of the four sites with diffe...
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