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- Title
- Three-Dimensional Inversion Technique in Ocean Acoustics Using the Parabolic Equation Method.
- Creator
- Roa, Camilo Carlos, Frisk, George V., Florida Atlantic University, College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
-
A three-dimensional parabolic equation (PE) and perturbation approach is used to invert for the depth- and range-dependent geoacoustic characteristics of the seabed. The model assumes that the sound speed profile is the superposition of a known range-independent profile and an unknown depth- and range-dependent perturbation. Using a Green’s function approach, the total measured pressure field in the water column is decomposed into a background field, which is due to the range-independent...
Show moreA three-dimensional parabolic equation (PE) and perturbation approach is used to invert for the depth- and range-dependent geoacoustic characteristics of the seabed. The model assumes that the sound speed profile is the superposition of a known range-independent profile and an unknown depth- and range-dependent perturbation. Using a Green’s function approach, the total measured pressure field in the water column is decomposed into a background field, which is due to the range-independent profile, and a scattered field, which is due to the range-dependent perturbation. When the Born approximation is applied to the resulting integral equation, it can be solved for the range-dependent profile using linear inverse theory. Although the method is focused on inverting for the sound speed profile in the bottom, it can also invert for the sound speed profile in the water column. For simplicity, the sound speed profile in the water column was assumed to be known with a margin of error of ± 5 m/s. The range-dependent perturbation is added to the index of refraction squared n2(r), rather than the sound speed profile c(ro). The method is implemented in both Cartesian (x,y,z) and cylindrical (r,q,z) coordinates with the forward propagation of the field in x and r, respectively. Synthetic data are used to demonstrate the validity of the method [1]. Two inversion methods were combined, a Monte Carlo like algorithm, responsible for a starting approximation of the sound speed profile, and a steepest descent method, that fine-tuned the results. In simulations, the inversion algorithm is capable of inverting for the sound speed profile of a flat bottom. It was tested, for three different frequencies (50 Hz, 75 Hz, and 100 Hz), in a Pekeris waveguide, a range-independent layered medium, and a range-dependent medium, with errors in the inverted sound speed profile of less than 3%. Keywords: Three-dimensional parabolic equation method, geoacoustic inversion, range-dependent sound speed profile, linear inversion, Born approximation, Green’s functions.
Show less - Date Issued
- 2017
- PURL
- http://purl.flvc.org/fau/fd/FA00004868, http://purl.flvc.org/fau/fd/FA00004868
- Subject Headings
- Ocean tomography., Ocean bottom., Born approximation., Green's functions.
- Format
- Document (PDF)
- Title
- Prey selectivity of the fishes Stephanolepis hispidus and Histrio histrio on the Sargassum shrimps Latreutes fucorum and Leander tenuicornis.
- Creator
- Hutchinson, Kimberly A., Florida Atlantic University, Brooks, W. Randy
- Abstract/Description
-
Predator-prey relationships were studied between the shrimps Latreutes fucorum and Leander tenuicornis and the predatory fishes Stephanolepis hispidus and Histrio histrio, all found within pelagic Sargassum communities. Average survival times of shrimps were compared in species, size/density, and habitat selection studies. The results showed that S. hispidus had a preference for prey species while H. histrio did not. 30 mm shrimp survived longer than the 10 mm shrimp for both S. hispidus and...
Show morePredator-prey relationships were studied between the shrimps Latreutes fucorum and Leander tenuicornis and the predatory fishes Stephanolepis hispidus and Histrio histrio, all found within pelagic Sargassum communities. Average survival times of shrimps were compared in species, size/density, and habitat selection studies. The results showed that S. hispidus had a preference for prey species while H. histrio did not. 30 mm shrimp survived longer than the 10 mm shrimp for both S. hispidus and H. histrio. Density was a factor in the survival times of the 20 mm shrimps with S. hispidus only. L. tenuicornis survived longer in artificial Sargassum habitats with H. histrio. The larger shrimps survived longer in the artificial habitats than the smaller shrimps with S. hispidus. Both fish predators employ optimal foraging strategies with similarities and differences, the latter of which are likely related to behavioral differences in the these predator and prey.
Show less - Date Issued
- 2004
- PURL
- http://purl.flvc.org/fcla/dt/13156
- Subject Headings
- Predation (Biology), Fishes--Ecology, Ocean bottom ecology, Marine animals
- Format
- Document (PDF)
- Title
- An investigation of the acoustic field in wedge-shaped scale models of continental shelf regions.
- Creator
- House, Ian Geoffrey., Florida Atlantic University, Glegg, Stewart A. L., College of Engineering and Computer Science, Department of Ocean and Mechanical Engineering
- Abstract/Description
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The acoustic field in the ocean is difficult to model theoretically, due to the complexity of the environment. This is particularly true if the water depth is range dependent, such as in the coastal region, where a fully three dimensional description is required. Propagation effects result in horizontal refraction, shadow zones, and the existence of regions with strong interference patterns. As a result, all of the existing theoretical models are based on significant simplifying assumptions....
Show moreThe acoustic field in the ocean is difficult to model theoretically, due to the complexity of the environment. This is particularly true if the water depth is range dependent, such as in the coastal region, where a fully three dimensional description is required. Propagation effects result in horizontal refraction, shadow zones, and the existence of regions with strong interference patterns. As a result, all of the existing theoretical models are based on significant simplifying assumptions. One such assumption is to model a region of the ocean as a water column overlying a planar sloping bottom. To test the accuracy of these theories model scale measurements of the acoustic field under highly controlled conditions have been undertaken in this study. Two experiments were performed on models with a sloping bottom. The first model consisted of a fast fluid bottom, and the second model consisted of a thin epoxy layer, to model a sediment, overlying a concrete layer, which modelled the substrate rock. The measurements performed included pulse, CW traverse, and depth profile measurements in both the across slope and down slope directions, in order to demonstrate the three dimensional features of the field. The features of the results are discussed and where possible are compared with existing theories. The results indicated that the three dimensional propagation effects in a fluid bottom wedge are described accurately by a theoretical model which uses an effective depth correction. No three dimensional theory was available for the shear wave supporting bottom case but the fluid bottom theory was found to provide accurate predictions. Down slope propagation over a shear wave supporting bottom was also shown to be accurately predicted using a two dimensional finite element parabolic equation code.
Show less - Date Issued
- 1991
- PURL
- http://purl.flvc.org/fcla/dt/12284
- Subject Headings
- Underwater acoustics--Measurement, Ocean bottom, Continental shelf
- Format
- Document (PDF)
- Title
- Interpretation of seafloor topologies based on IKONOS satellite imagery of a shallow-marine carbonate platform: Florida Bay to the Florida Reef Tract.
- Creator
- Steinle, Jacob Thomas., Charles E. Schmidt College of Science, Department of Geosciences
- Abstract/Description
-
A benthic environments classification system is devised from digital interpretations of multi-spectral IKONOS satellite imagery for 1,360 km2 of the carbonate platform and presented in a comprehensive digitized map. The classification scheme is designed as a 7th order hierarchical structure that integrates 5 Physiographic Realms, 24 Morphodynamic Zones, 11 Geoforms, 39 Landforms, 6 dominant surface sediment types, 9 dominant biological covers and 3 densities of biological covers for the...
Show moreA benthic environments classification system is devised from digital interpretations of multi-spectral IKONOS satellite imagery for 1,360 km2 of the carbonate platform and presented in a comprehensive digitized map. The classification scheme is designed as a 7th order hierarchical structure that integrates 5 Physiographic Realms, 24 Morphodynamic Zones, 11 Geoforms, 39 Landforms, 6 dominant surface sediment types, 9 dominant biological covers and 3 densities of biological covers for the description of benthic environments. Digital analysis of the high-resolution (4 m) IKONOS imagery employed ESRI's ArcMap to manually digitize 412 mapping units at a scale of 1:6,000 differentiated by spectral reflectance, color tones, and textures of seafloor topologies. The context of each morphodynamic zone is characterized by the content and areal distribution (in km2) of geomorphic forms and biological covers. Over 58% of the mapping area is occupied by sediment flats, and seagrasses are colonized in almost 80% of the topologies.
Show less - Date Issued
- 2011
- PURL
- http://purl.flvc.org/FAU/3174075
- Subject Headings
- Submarine topography, Marine sediments, Remote sensing, Marine ecosystem management, Ocean bottom, Sampling, Ocean bottom, Sampling, Coral reef ecology
- Format
- Document (PDF)
- Title
- A 3-D laser line scanner for outcrop scale studies of seafloor features.
- Creator
- Kocak, D. M., Caimi, F. M., Das, Partha S., Karson, J. A., Harbor Branch Oceanographic Institute
- Date Issued
- 1999
- PURL
- http://purl.flvc.org/FCLA/DT/3351977
- Subject Headings
- Scanning systems, Cartography--Laser use in, Geological maps, Submersibles, Ocean bottom--Maps
- Format
- Document (PDF)
- Title
- Sediment classification of the sea floor using the Chirp Sonar and the Biot model.
- Creator
- Beaujean, Pierre-Philippe, Florida Atlantic University, LeBlanc, Lester R.
- Abstract/Description
-
A new method is proposed to infer the geotechnical properties of the sea floor from its response to the frequency-modulated pulses emitted by the subbottom profiler called Chirp Sonar. The environment is assumed to be a multilayered medium, composed of homogeneous layers, or an inhomogeneous half-space with depth-dependent properties. The acoustic response of the sediment is computed using the Biot-Stoll theory. The Levenberg-Marquardt method is applied to fit the synthetic response to the...
Show moreA new method is proposed to infer the geotechnical properties of the sea floor from its response to the frequency-modulated pulses emitted by the subbottom profiler called Chirp Sonar. The environment is assumed to be a multilayered medium, composed of homogeneous layers, or an inhomogeneous half-space with depth-dependent properties. The acoustic response of the sediment is computed using the Biot-Stoll theory. The Levenberg-Marquardt method is applied to fit the synthetic response to the experimental response of an homogeneous layer overlying the sea floor. The porosity, the permeability, the mean grain diameter, the mass density, the bulk modulus and the shear modulus within this sediment layer can be estimated. A multilayered medium with depth-dependent properties could be applied to this inversion technique in the future.
Show less - Date Issued
- 1995
- PURL
- http://purl.flvc.org/fcla/dt/15208
- Subject Headings
- Marine sediments--Acoustic properties, Underwater acoustics--Measurement, Ocean bottom, Sonar
- Format
- Document (PDF)
- Title
- Summary of seafloor mapping and benthic sampling in 200-2000m, from North Carolina through Florida.
- Creator
- Arendt, M. D., Barans, C. A., Sedberry, G. R., Van Dolah, R. F., Reed, John K., Ross, S. W.
- Date Issued
- 2003
- PURL
- http://purl.flvc.org/FCLA/DT/3318904
- Subject Headings
- Submarine topography--Atlantic Coast (U.S.)--Maps, Ocean bottom--Maps, Benthos--Habitat--Maps, Benthos--Sampling
- Format
- Document (PDF)