Correlation of deep ocean noise (0.4–30 Hz) with wind, and the Holu Spectrum—A worldwide constant

McCreery, Charles S.; Duennebier, F. K.; Sutton, George H.

doi:10.1121/1.405838

Cited by 69 publications

(75 citation statements)

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“…8). The data from this study are not directly comparable to the McCreery et al (1993) analysis because the previous study removed loud transient signals (earthquakes, close ships, seismic airgun activity) with a power level at least 3 dB greater than the level of the two adjacent samples in the time series, whereas the spectra presented in Fig. 8 include all transients.…”

Section: Discussionmentioning

confidence: 58%

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Is low frequency ocean sound increasing globally?

Miksis‐Olds

Nichols

2016

The Journal of the Acoustical Society of America

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Low frequency sound has increased in the Northeast Pacific Ocean over the past 60 yr [Ross (1993) Acoust. Bull. 18, 5–8; (2005) IEEE J. Ocean. Eng. 30, 257–261; Andrew, Howe, Mercer, and Dzieciuch (2002) J. Acoust. Soc. Am. 129, 642–651; McDonald, Hildebrand, and Wiggins (2006) J. Acoust. Soc. Am. 120, 711–717; Chapman and Price (2011) J. Acoust. Soc. Am. 129, EL161–EL165] and in the Indian Ocean over the past decade, [Miksis-Olds, Bradley, and Niu (2013) J. Acoust. Soc. Am. 134, 3464–3475]. More recently, Andrew, Howe, and Mercer's [(2011) J. Acoust. Soc. Am. 129, 642–651] observations in the Northeast Pacific show a level or slightly decreasing trend in low frequency noise. It remains unclear what the low frequency trends are in other regions of the world. In this work, data from the Comprehensive Nuclear-Test Ban Treaty Organization International Monitoring System was used to examine the rate and magnitude of change in low frequency sound (5–115 Hz) over the past decade in the South Atlantic and Equatorial Pacific Oceans. The dominant source observed in the South Atlantic was seismic air gun signals, while shipping and biologic sources contributed more to the acoustic environment at the Equatorial Pacific location. Sound levels over the past 5–6 yr in the Equatorial Pacific have decreased. Decreases were also observed in the ambient sound floor in the South Atlantic Ocean. Based on these observations, it does not appear that low frequency sound levels are increasing globally.

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Section: Discussionmentioning

confidence: 58%

“…Although this work showed a recent decreasing trend in specific components of low frequency sound levels at Wake Island, it is likely that there has been an overall increase compared to the early 1980s (McCreery et al, 1993) (Fig. 8).…”

Section: Discussionmentioning

confidence: 99%

Is low frequency ocean sound increasing globally?

Miksis‐Olds

Nichols

2016

The Journal of the Acoustical Society of America

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“…The noise at the southern hydrophone, U26, may differ because the instrument is deeper than the others. McCreery et al (1988 and1993) has found from using hydrophones near Wake Island that the noise levels between 3 and 6 Hz do not vary much with depth. They do see differences in the 10 to 20…”

Section: Instrumentationmentioning

confidence: 99%

Performance of an island seismic station for recording T-phases

Hanson¹

1998

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As part of the International Monitoring System (IMS) a worldwide hydroacoustic network consisting of 6 hydrophone and 5 island seismic stations has been planned which will monitor for underwater or low altitude atmospheric explosions. Data from this network is to be integrated with other IMS networks monitoring the Comprehensive Nuclear Test-Ban Treaty. The seismic (T-phase) stations are significantly less sensitive than hydrophones to ocean borne acoustic waves. T-phase signal strength-at seismic stations depends on the amplitude of the signal in the water column, the hydroacoustic-seismic conversion efficiency, and loss on the seismic portion of the path through the island. In order to understand how these factors influence the performance of T-phase stations seismic and hydroacoustic data are examined from instruments currently deployed on or around Ascension Island in the South Atlantic Ocean.T-phase recordings for the last 3 years have been collected from the GSN seismic station ASCN on Ascension Island. Surrounding the island are 5 hydrophones which are part of the U.S. Air Force Missile Impact Locating System (MILS). Data from this system have been obtained for some of the events observed at ASCN. Four of the hydrophones are located within 30 km of the coast while the fifth instrument is 100 km to the south.Amplitude spectral estimates of the signal-to-noise levels (SNL) are computed and generally peak between 3 and 8 Hz for both the seismometer and hydrophone data. The seismic SNL generally decays to 1 between 10 and 15 Hz while the hydrophone SNL is still large well above 20 Hz. The ratios of the hydrophone-to-seismometer SNL, at their peak in energy, range between 10 and 100 (20-40 dB) unless a hydrophone is partially blocked by the Ascension Island landmass. This ratio varies with respect to the azimuth of the arriving T-phase due to amplitude variations in both the hydrophone and seismic data. Signal loss at the hydrophones due to island blockage is modeled numerically and then corrected for. Variations between the corrected hydroacoustic amplitudes and seismic amplitudes are 3 compared with physical parameters such as the gradient of the topography at the islandocean interface. T-phases can have various modal structures which will couple into the island differently. Thus events from the same direction have different signal loss.

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“…, sound in the deep ocean is almost invariant (McCreery et al 1993). This is taken to indicate that, at any wave frequency 0.5 , f w , 5 Hz (6.5 , l , 0.06 m), the wavenumber spectrum under these conditions is both isotropic in direction and also constant in amplitude.…”

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confidence: 99%

Wind Sea behind a Cold Front and Deep Ocean Acoustics

Farrell¹,

Berger

Bidlot

et al. 2016

Journal of Physical Oceanography

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A rapid and broadband (1 h, 1 , f , 400 Hz) increase in pressure and vertical velocity on the deep ocean floor was observed on seven instruments comprising a 20-km array in the northeastern subtropical Pacific. The authors associate the jump with the passage of a cold front and focus on the 4-and 400-Hz spectra. At every station, the time of the jump is consistent with the front coming from the northwest. The apparent rate of progress, 10-20 km h 21 (2.8-5.6 m s 21 ), agrees with meteorological observations. The acoustic radiation below the front is modeled as arising from a moving half-plane of uncorrelated acoustic dipoles. The half-plane is preceded by a 10-km transition zone, over which the radiator strength increases linearly from zero. With this model, the time derivative of the jump at a station yields a second and independent estimate of the front's speed, 8.5 km h 21 (2.4 m s 21). For the 4-Hz spectra, the source physics is taken to be Longuet-Higgins radiation. Its strength depends on the quantity F 2 z I, where F z is the wave amplitude power spectrum and I the overlap integral. Thus, the 1-h time constant observed in the bottom data implies a similar time constant for the growth of the wave field quantity F 2 z I behind the front. The spectra at 400 Hz have a similar time constant, but the jump occurs 25 min later. The implications of this difference for the source physics are uncertain.

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Correlation of deep ocean noise (0.4–30 Hz) with wind, and the Holu Spectrum—A worldwide constant

Cited by 69 publications

References 0 publications

Is low frequency ocean sound increasing globally?

Is low frequency ocean sound increasing globally?

Performance of an island seismic station for recording T-phases

Wind Sea behind a Cold Front and Deep Ocean Acoustics

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