Environmental Effects on Low Frequency Transmission Loss in the Gulf of Mexico

Brunson, Burlie A.; Truxillo, M. M.; Evans, Richard B.

doi:10.21236/adc029543

“…9 The range-averaged maximum slope of the margin surrounding the Catoche Tongue is 18:58, which is comparatively steep for ocean environments. To put this in context, typical angles are 38 to 68 for continental slopes and submarine canyons, and 0:58 to 18 for continental rises.…”

Section: Description Of Experimentsmentioning

confidence: 98%

“…The positive attenuation gradient in the upper 300 m of ooze is consistent with previous modeling efforts. 9 The acoustic field is insensitive to the attenuation values deeper than 300 m because of the upward refracting sound-speed profile in the ooze. The combination of the nonlinear sound-speed profile and positive attenuation gradient created a relatively abrupt transition between low-order modes that were weakly attenuated and high-order modes that were highly attenuated.…”

Section: B Environmental Representationmentioning

confidence: 99%

“…Portions of the acoustic record from the CSIII experiment have been analyzed previously, 9,10 but the SUS events displaying the second class of arrivals are presented here for the first time. These data and the analysis presented in this manuscript are unique in that the two arrival classes are visible in the omnidirectional time series and that the timing between the arrivals is the primary feature by which 3D propagation is explained.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Evidence of three-dimensional acoustic propagation in the Catoche Tongue

Sagers

¹

,

Ballard

²

,

Knobles

³

2014

The Journal of the Acoustical Society of America

12

0

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This paper presents observations of two classes of acoustic arrivals recorded on a sparsely populated vertical line array (VLA) moored in the center of the Catoche Tongue, a major reentrant in the Campeche Bank in the southeastern Gulf of Mexico. The acoustic signals were generated by signals underwater sound (SUS) located 50-80 km from the VLA. The first class of arrivals was identified as resulting from a direct (non-horizontally refracted) path. Then following a quiescent period, a second, more diffuse class of arrivals is observed and is believed to be the result of horizontal refraction from the margin of the Tongue. A spectral analysis of the measured data revealed that both classes of arrivals were characterized by the source spectrum associated with SUS. Additionally, the difference in time between the onset of the first and second class of arrivals observed as a function of range from the VLA is consistent with the relative difference in the length of the direct and refracted paths. The observations are further supported by a three-dimensional (3D) acoustic propagation computation that reproduces many of the features of the measured data and provides additional insight into the details of the 3D propagation.

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“…3(a). assessed the stratigraphic structure of the seabed was from seismograms and core data [Buffler et al (1984); Worzel (1973); Shaub (1987); Brunson et al (1980)]. Fig.…”

Section: Modeling Of 3d Propagation Effects Observed In the Church Stmentioning

confidence: 99%

Acoustic Modeling Using a Three-Dimensional Coupled-Mode Model

Ballard¹

2013

0

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The overall goal of this research is the development of an accurate and reliable propagation model applicable to environments which exhibit strong range dependence in all three spatial dimensions. OBJECTIVES The objective of this work is to gain an understanding the physics of propagation in continental shelf areas, specifically horizontal refraction and mode coupling induced by three-dimensional (3D) inhomogeneities in the waveguide. A coupled-mode approach has been applied for this purpose. The coupled-mode approach is attractive for solving problems involving 3D propagation for several reasons. First, this technique provides intuitive results for understanding the features responsible for observed propagation effects in range-dependent environments. For example, upslope propagation is characterized by acoustic energy radiated into the bottom at discrete depths associated with mode cutoff. The modal decomposition of the acoustic field has also been used to describe horizontal refraction in a wedge-shaped ocean, for which the single-mode interference pattern associated with rays launched up and across the shelf has been well documented [Weinberg and Burridge (1974)]. Furthermore, coupled-mode solutions can be highly accurate and have been used for benchmarking solutions to range-dependent problems [Jensen and Ferla (1990)]. In order to appreciate the limitations of existing 3D models, it is necessary to have methods which can provide reference solutions for comparison. APPROACH A 3D acoustic propagation model based on the stepwise coupled-mode approach [Evans (1983)] implemented as a single-scatter solution has been developed. This technique is based on a hybrid modeling approach for which normal modes supply the vertical dependence and a parabolic equation (PE) solution provides the horizontal dependence. The inhomogeneous Helmholtz equation for pressure P(r, θ , z) at range r, azimuth θ , and depth z from a point continuous wave source of amplitude S(ω), 1 DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.

show abstract

Acoustic Modeling Using a Three-Dimensional Coupled-Mode Model

Ballard

¹

2012

0

View full text Add to dashboard Cite

The overall goal of this research is the development of an accurate and reliable propagation model applicable to environments which exhibit strong range dependence in all three spatial dimensions. OBJECTIVES The objective of this work is to gain an understanding the physics of propagation in continental shelf areas, specifically horizontal refraction and mode coupling induced by three-dimensional (3D) inhomogeneities in the waveguide. A coupled-mode approach has been applied for this purpose. The coupled-mode approach is attractive for solving problems involving 3D propagation for several reasons. First, this technique provides intuitive results for understanding the features responsible for observed propagation effects in range-dependent environments. For example, upslope propagation is characterized by acoustic energy radiated into the bottom at discrete depths associated with mode cutoff. The modal decomposition of the acoustic field has also been used to describe horizontal refraction in a wedge-shaped ocean, for which the single-mode interference pattern associated with rays launched up and across the shelf has been well documented [Weinberg and Burridge (1974)]. Furthermore, coupled-mode solutions can be highly accurate and have been used for benchmarking solutions to range-dependent problems [Jensen and Ferla (1990)]. In order to appreciate the limitations of existing 3D models, it is necessary to have methods which can provide reference solutions for comparison. APPROACH A 3D acoustic propagation model based on the stepwise coupled-mode approach [Evans (1983)] implemented as a single-scatter solution has been developed. This technique is based on a hybrid modeling approach for which normal modes supply the vertical dependence and a parabolic equation (PE) solution provides the horizontal dependence. The inhomogeneous Helmholtz equation for pressure P(r, θ , z) at range r, azimuth θ , and depth z from a point continuous wave source of amplitude S(ω), 1 DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.

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Environmental Effects on Low Frequency Transmission Loss in the Gulf of Mexico

Cited by 3 publications

References 0 publications

Evidence of three-dimensional acoustic propagation in the Catoche Tongue

Evidence of three-dimensional acoustic propagation in the Catoche Tongue

Acoustic Modeling Using a Three-Dimensional Coupled-Mode Model

Acoustic Modeling Using a Three-Dimensional Coupled-Mode Model

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