Scattering by objects buried in underwater sediments: Theory and experiment

Lim, Raymond; Lopes, Joseph L.; Hackman, Roger H.; Todoroff, Douglas G.

doi:10.1121/1.406719

Cited by 57 publications

(39 citation statements)

References 6 publications

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“…For simple near-spherical target shapes proud or buried in a flat ocean bottom, scattering predictions are generated from high-fidelity solutions based on the T-matrix method [4]. Last year [5],…”

Section: Approachmentioning

confidence: 99%

Modeling Sonar Responses of Targets Deployed On or In the Seafloor

Lim

2011

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Document Number: N0001411WX20015 LONG-TERM GOALRecent interest in understanding the potential advantages of nonconventional detection configurations, such as bistatic vs monostatic, has driven efforts to initiate the model refinements needed to study these configurations for simple targets deployed proud or buried on the seafloor. A benchmark quality capability for these targets is utilized so that unambiguous results are available for physical interpretation and analysis, both in laboratory sonar measurements as well as in sonar field tests using the Naval Surface Warfare Center Panama City Division's (NSWC PCD) synthetic aperture sonar (SAS) systems. The long term goal of this effort is to investigate and compare how the physics of a target embedded in a given environment and sensed under different detection modes can affect both target signal-to-noise (SNR) and classification. This knowledge can then be used to improve sonar detection and classification of bottom targets. OBJECTIVESOne objective is to generate high fidelity datasets to help understand carefully controlled measurements in the scale-model sonar test bed operated at NSWC PCD [1], which can be configured to collect SAS target data along both linear and circular tracks. Interest in circular tracks has grown recently because circular SAS (CSAS) processing may provide imagery with better shape resolution for classification purposes. The comparisons made were used to gain insight to the fidelity of data that can be collected in the test bed by helping to separate target from noise phenomena and by helping to interpret target phenomena that might be useful for target classification. Furthermore, the datasets created are used to study the effectiveness of processing algorithms for isolating signal from noise.A second objective this year is to test solutions recently proposed by Waterman [2] for stabilizing the spherical-basis T-matrix for nonspherical shapes at high frequencies. This would yield a more practical T-matrix solution than the spheroidal-basis version [3] currently used for elongated shapes, which can still be limited by how accurately high order spheroidal functions can be computed. APPROACHFor simple near-spherical target shapes proud or buried in a flat ocean bottom, scattering predictions are generated from high-fidelity solutions based on the T-matrix method [4]. Last year [5],

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Section: Approachmentioning

confidence: 99%

Modeling Sonar Responses of Targets Deployed On or In the Seafloor

Lim

2011

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“…For example, elimination of the first assumption is necessary to take into account scatterers located on the bottom surface or not buried completely but rather exposed in the water. In this case, analytical solutions are complicated, but can be analyzed numerically [Lim et al 1993and Lim 1998, Fawcett 1996, Fawcett and Lim 2003, Zampolli et al 2008. There is also a simpler semi-phenomenological approach, using ray considerations, that can be useful at high enough frequencies.…”

Section: °30mentioning

confidence: 99%

Scattering from inclusions in Marine Sediments: SAX04 Data/Model Comparisons

Ivakin¹

2008

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Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching 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 information, including suggestions for reducing this burden to Washington Headquarters Service, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188) Washington, DC 20503. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY) 08-14-2008 REPORT TYPE Final Technical DATES COVERED (From -To AUTHOR(S)Ivakin, Anatoliy N. 5f. WORK UNIT NUMBER PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)Applied SPONSOR/MONITOR'S ACRONYM(S)APL-UW SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)Office of Naval Research 875 North Randolph St. Arlington, VA 22203-1995 SPONSORING/MONITORING AGENCY REPORT NUMBER DISTRIBUTION AVAILABILITY STATEMENTApproved for public release; distribution is unlimited SUPPLEMENTARY NOTES ABSTRACTThe role of discrete scatterers in marine sediments is evaluated based on acoustic and environmental measurements at the shallow water sediment acoustics experiment, SAX04, and shown to be significant. The sediment at SAX04 site was complicated and characterized as a mostly medium sand / mud mixture. Analysis of the sediment samples showed presence of a small volume portion of arger particles, such as coarse sand fraction and shell fragments, which were considered as inclusions, or sparsely distributed discrete scatterers, embedded in a homogeneous effective fluid with parameters corresponding to medium sand or mud sediment frame. This analysis provided also the size distributions for both types of inclusions, coarse sand particles and shells, which were used as inputs to a model of incoherent discrete scattering in the sediment. It is demonstrated that this approach in general is capable to provide a reasonable explanation of both frequency and angular dependencies of the SAX04 bottom backscattering strength, and discrete scattering from the sediment inclusions can be a significant mechanism of the SAX04 high frequency reverberation in a wide range of grazing angles (15 to 50 degrees) and frequencies (30 kHz to 500 kHz). SUBJECT TERMSbackscattering strength, medium sand and mud sediments, shell fragments, coarse sand inclusions, particle size distribution Abstract-The role of discrete scatterers in marine sediments is evaluated based on acoustic and environmental measurements at the shallow water sediment acoustics experiment, SAX04, and shown to be significant. The sediment at SAX04 site was complicated and characterized as a mostly medium sand / mud mixture. Analysis of the sediment samples showed presence of a small volume portion of larger particles, such as coarse sand fract...

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“…A sound wave that reaches the interface not only is reflected by the surface of sea bottom but also is affected by refraction and scattering. Lim et al [3] concluded that if the beam is scanned over the object at shallow grazing angles, the scattering of evanescent waves may be an important part of the received echo.…”

Section: Introductionmentioning

confidence: 99%

“…Swift and Stephen [2] computed the two-dimensional scattered field by the finite-difference method for an incident Gaussian pulse beam at 15 grazing angle. Lim et al [3] studied the scattering of sound by objects buried in underwater sediments in the context of an exactly soluble model. The main problem in studying the detection of a buried object is existence of the interface between the water and the sediment.…”

Section: Introductionmentioning

confidence: 99%

Sound beam scanning in sediment layer using phase conjugated pseudo sound source

Tsurugaya¹,

Kikuchi

Iwase

et al. 2008

Acoust. Sci. & Tech.

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When an object that is buried underwater in a sediment layer is detected from the diagonal, detection is often hampered by reflection from the bottom surface. Stated in different terms, the sound-wave energy that reaches the object is small because of reflection and refraction that occurs at the bottom surface when a sound wave is applied to the object in the sediment for diagonal detection. To alleviate that problem, a pseudo sound source can be set up in the sediment layer. The sound wave radiated from the pseudo sound source is then received by a time-reversal array. The sound wave can be injected into the sediment layer by reversing the received signal with time, and radiating it again from the time-reversal array. The beam can hit the target through movement of this pseudo sound source along the bottom surface. The sound wave that hits the target is reflected and returns in water. The sound wave is subsequently reflected many times at the surface and bottom, and is diffused over time. The passive-phase conjugate processing is then given to the received diffusing signal to reduce this diffusion. The pulse is compressed by this processing, thereby obtaining the target position.

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Scattering by objects buried in underwater sediments: Theory and experiment

Cited by 57 publications

References 6 publications

Modeling Sonar Responses of Targets Deployed On or In the Seafloor

Modeling Sonar Responses of Targets Deployed On or In the Seafloor

Scattering from inclusions in Marine Sediments: SAX04 Data/Model Comparisons

Sound beam scanning in sediment layer using phase conjugated pseudo sound source

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