Computation of Noise Directionality, Coherence and Array Response in Range Dependent Media With Canary

Harrison, Chris H.; Brind, R. J.; Cowley, Angela

doi:10.1142/s0218396x01000528

Cited by 6 publications

(3 citation statements)

References 8 publications

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“…Here, a simpler ray approach is used which involves far fewer calculations yet provides (arguably) a better solution than full-wave models [7]. A broad-band of frequencies can be computed at arbitrarily high frequency in a fraction of the time needed for wave calculations and this type of calculation is included in the noise coherence model CANARY [8,9]. A ray based derivation will be presented here for the noise cross-spectral density function that follows Harrison [7] but simplified by only considering vertically separated…”

Section: High Frequency Ambient Noise Modeling and Estimating Reflectmentioning

confidence: 99%

High-Frequency Geoacoustic Inversion of Ambient Noise Data Using Short Arrays

Siderius¹,

Harrison²

2004

AIP Conference Proceedings

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Ocean ambient noise is generated in many ways such as from winds, rain and shipping. A technique has recently been developed (Harrison and Simons, J. Acoust. Soc. Am, Vol. 112 no. 4, 2002) that uses the vertical directionality of ambient noise to determine seabed properties. It was shown that taking a ratio of upward looking beams to downward produces an estimate of the reflection loss. This technique was applied to data in the 200-1500 Hz band using a 16-m vertical array. Extending this to higher frequencies allows the array length to be substantially shortened and greatly reduces interference from shipping. If array lengths can be reduced to about 1 m then it may be possible to hull-mount or tow such an array from a surface ship or submerged vehicle (e.g. an autonomous underwater vehicle). Although this seems attractive the noise is primarily generated by wind which in turn causes a rough sea-surface and bubbles and these factors combined with increased volume attenuation may degrade this type of reflection loss estimate at high frequencies.In this paper, we examine measured noise data from the October 2003 ElbaEx experiment using a 5.5 m array in the 1-4 kHz frequency band. Results indicate the noise field is predictable with modeling and the ratio of upward looking to downward looking beams produces an approximation to the reflection loss which can be inverted for seabed properties. For short arrays (a 1 m aperture is considered here), the beamforming is not ideal over a broad-band of frequencies. The beams are broadened and this leads to an up/down ratio that does not produce a good estimate of reflection loss. This can be especially problematic at low grazing angles which is the part of the reflection loss curve that is often most important to estimate correctly. Techniques will be presented for mitigating the impact of beamwidth and grating lobes on estimating the seabed properties.

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Section: High Frequency Ambient Noise Modeling and Estimating Reflectmentioning

confidence: 99%

High-Frequency Geoacoustic Inversion of Ambient Noise Data Using Short Arrays

Siderius¹,

Harrison²

2004

AIP Conference Proceedings

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“…The calculation of the vertical noise directivity is based on [7], but modified to allow for arbitrary surface source directionality [6] and also includes a volume scattering mechanism [5]. Once the ambient noise directionality is obtained, we calculate a Cross Spectral Density (CSD) matrix for an array of elements, as described by [7,9]. The CSD for shipping is separately calculated by incoherently summing the CSD matrices of individual ships.…”

Section: Theorymentioning

confidence: 99%

“…Of note are the significant differences in the shape of VND for angles outside the notch. Via [9,10], VND can be mapped to a CSD matrix for an arbitrary array of elements. The implementation is straightforward and is not repeated here.…”

Section: Wind-generated Ambient Vertical Noise Directivitymentioning

confidence: 99%

Mid- to high-frequency ambient noise anisotropy and notch-filling mechanisms

Ferat

Arvelo

2003

The Journal of the Acoustical Society of America

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Mid to high-frequency (1-20 kHz) noise is generally dominated by wind-driven wave activity but under certain conditions potentially exploitable ambient noise fields can be severely degraded by nearby ships, especially in the lower end of the band. The use of directive elements and adaptive methods are shown as possible ways to mitigate this problem. For a submerged receiver in a downward-refracting environment without nearby ships, a vertical noise notch that can offer increased array gain over the directivity index can be filled in by scattering from volume inhomogeneities. Just outside the notch, the ambient noise vertical directivity is sensitive to the assumed surface source directionality. A ray-based model is used to assess the sensitivity of the performance of a vertical line array and a volumetric array to these mechanisms in a tactically relevant environment.

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Research Issues and Applications of Oceanic Noise

Carey

Evans²

2010

Ocean Ambient Noise

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Computation of Noise Directionality, Coherence and Array Response in Range Dependent Media With Canary

Cited by 6 publications

References 8 publications

High-Frequency Geoacoustic Inversion of Ambient Noise Data Using Short Arrays

High-Frequency Geoacoustic Inversion of Ambient Noise Data Using Short Arrays

Mid- to high-frequency ambient noise anisotropy and notch-filling mechanisms

Research Issues and Applications of Oceanic Noise

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