Recovering the Acoustic Green’s Function from Ambient Noise Cross Correlation in an Inhomogeneous Moving Medium

Godin, Oleg A.

doi:10.1103/physrevlett.97.054301

Cited by 100 publications

(78 citation statements)

References 15 publications

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“…Theoretically predicted possibility of retrieving flow-induced non-reciprocity of the deterministic GFs from cross-correlation of diffuse sound fields (Godin, 2006) has been confirmed by Monte-Carlo simulations and verified in a field experiment .…”

Section: Work Completedmentioning

confidence: 70%

“…Deterministic acoustic travel times between receivers emerge as peaks of the envelope of the noise cross-correlation function evaluated through time-averages of products of acoustic pressures recorded at two points. In the case of moving fluids, our model shows the theoretically predicted (Godin, 2006) asymmetry in the position of the correlation peaks at positive and negative time delays, which reflects acoustic non-reciprocity and enables determination of the flow velocity vector .…”

Section: Resultsmentioning

confidence: 99%

“…Our theoretical approach is based on the flow reversal theorem (Godin, 1997), which is an extension of the reciprocity principle to moving media. The approach proved to be instrumental in deriving exact representations of the noise fields and their statistics in arbitrarily inhomogeneous, moving media in terms of deterministic GFs (Godin, 2006(Godin, , 2007(Godin, , 2009a(Godin, , 2010a. Moreover, the flow reversal theorem leads to important identities (often termed Ward identities), which relate surface and volume integrals of certain products of GFs to the GF value at a point and underlie exact and asymptotic local relations between diffuse noise cross-correlations and deterministic GFs (Godin, 2006(Godin, , 2007(Godin, , 2009a(Godin, , 2010a.…”

Section: Approachmentioning

confidence: 99%

“…Asymptotic approaches based on the stationary phase approximation (Snieder, 2004;Godin, 2006) and its extensions (Godin, 2009d(Godin, , 2010a have been used to determine the information content of two-point cross-correlation function of acoustic noise in the ocean. The asymptotic approaches have been also used to investigate the role of a finite correlation length of noise sources and of motion of the sources on the noise cross-and auto-correlation functions.…”

Section: Approachmentioning

confidence: 99%

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Emergence of the Green's Functions from Noise and Passive Acoustic Remote Sensing of Ocean Dynamics

Godin¹

2010

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LONG-TERM GOALS• To evaluate feasibility and determine physical limits of performance of a passive acoustic system for characterization of a time-varying ocean where ambient acoustic noise is utilized as a probing signal.• To develop a passive remote sensing technique for acoustic characterization of oceanic currents. OBJECTIVES1. To demonstrate theoretically emergence of the deterministic Green's functions (GFs) from crosscorrelations of noise due to sources distributed in a volume and on boundaries in inhomogeneous, fluid-solid environments with dissipation.2. To investigate a relation between the deterministic GFs and a two-point correlation function of noise in a low-frequency regime where stationary-point arguments become inapplicable.3. To quantify degradation of performance of passive remote sensing techniques due to ocean surface motion and other variations of underwater sound propagation conditions in time.4. To retrieve flow-induced non-reciprocity of acoustic phase and amplitude of the deterministic GFs from cross-correlation of diffuse sound fields generated as a result of scattering by inhomogeneities in the water column and/or by seafloor and sea surface roughness.5. To determine accuracy of current velocity measurements using acoustic travel time nonreciprocity retrieved from a two-point noise cross-correlation.6. To evaluate, for shallow-and deep-water scenarios, optimal parameters of a passive acoustic system for ocean temperature and current velocity measurements using cross-correlation of ambient noise and/or sound fields generated by sources of opportunity.

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Section: Work Completedmentioning

confidence: 70%

Section: Resultsmentioning

confidence: 99%

Section: Approachmentioning

confidence: 99%

Section: Approachmentioning

confidence: 99%

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Emergence of the Green's Functions from Noise and Passive Acoustic Remote Sensing of Ocean Dynamics

Godin¹

2010

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“…Wavefields generated by spatially distributed random sources are known to remain partially coherent at points separated by distances that are large compared to the wavelength, with the twopoint cross-correlation function of the random wavefields approximating the Green's function, which describes deterministic wave propagation between the two observation points (Lobkis & Weaver 2001;Snieder 2004;Roux et al 2004;Wapenaar 2004;Godin 2006;Gouédard et al 2008). Cross-correlation functions of pressure fluctuations in the ocean have been investigated in the 0.5-30 mHz band, where the correlations characterize deep-water infragravity waves and their sources (Webb 1986;Godin et al 2014b), and at acoustic frequencies above 1 Hz, where geoacoustic parameters of the seafloor (Brown et al 2014), spatial (Godin et al 2010) and temporal (Woolfe et al 2015) variations of the sound speed in water and ocean current velocity (Godin et al 2014a) have been retrieved from noise cross-correlations.…”

Section: Introductionmentioning

confidence: 99%

Long-range correlations of microseism-band pressure fluctuations in the ocean

Ball

Godin

Evers

et al. 2017

The Journal of the Acoustical Society of America

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We investigate the spatial coherence of underwater infrasonic noise using a yearlong time series measured by hydrophones moored off Ascension Island. Qualitative agreement with observed cross-correlations is achieved using a simple range-dependent model, constrained by earlier, active tomographic studies in the area. In particular, the model correctly predicts the existence of two weakly dispersive normal modes in the microseism frequency range, with the group speed of one of the normal modes being smaller than the sound speed in water. The agreement justifies our interpretation of the peaks of the measured cross-correlation function of ambient noise as modal arrivals, with dispersion that is sensitive to crustal velocity structure. Our observations are consistent with Scholte to Moho head wave coupled propagation, with double mode conversion occurring due to the bathymetric variations between receivers. We thus demonstrate the feasibility of interrogating crustal properties using noise interferometry of moored hydrophone data at ranges in excess of 120 km.

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Interferometry of infragravity waves off New Zealand

et al. 2014

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Wave interferometry is a remote sensing technique, which is increasingly employed in helioseismology, seismology, and acoustics to retrieve parameters of the propagation medium from twopoint cross-correlation functions of random wavefields. Here we apply interferometry to yearlong records of seafloor pressure at 28 locations off New Zealand's South Island to investigate propagation and directivity properties of infragravity waves away from shore. A compressed cross-correlation function technique is proposed to make the interferometry of dispersive waves more robust, decrease the necessary noise averaging time, and simplify retrieval of quantitative information from noise cross correlations. The emergence of deterministic wave arrivals from cross correlations of random wavefields is observed up to the maximum range of 692 km between the pressure sensors in the array. Free, linear waves with a strongly anisotropic distribution of power flux density are found to be dominant in the infragravity wavefield. Lowest-frequency components of the infragravity wavefield are largely isotropic. The anisotropy has its maximum in the middle of the spectral band and decreases at the high-frequency end of the spectrum. Highest anisotropy peaks correspond to waves coming from portions of the New Zealand's shoreline. Significant contributions are also observed from waves propagating along the coastline and probably coming from powerful sources in the northeast Pacific. Infragravity wave directivity is markedly different to the east and to the west of the South Island. The northwest coast of the South Island is found to be a net source of the infragravity wave energy.

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Recovering the Acoustic Green’s Function from Ambient Noise Cross Correlation in an Inhomogeneous Moving Medium

Cited by 100 publications

References 15 publications

Emergence of the Green's Functions from Noise and Passive Acoustic Remote Sensing of Ocean Dynamics

Emergence of the Green's Functions from Noise and Passive Acoustic Remote Sensing of Ocean Dynamics

Long-range correlations of microseism-band pressure fluctuations in the ocean

Interferometry of infragravity waves off New Zealand

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