Tidal modulation of very-low-frequency and ultra-low-frequency ambient noise levels.

Several years of continuous low-frequency underwater ambient noise data from 0.1 to 125 Hz have been made available for examination by the United Nations Comprehensive Nuclear Test Ban Treaty Organization. Narrow-band noise time records between 0.

Bearing Stake 1977 revisited: An understanding of ambient sound sources in the Indian Ocean.

A previous analysis of 1977 passive acoustic recordings in the Indian Ocean focused on sound pressure levels (SPLs) and showed that SPLs were slightly depth dependent and highly influenced by shipping activities [Wagstaff and Aitkenhead, IEEE J. Ocean. Eng.

Use of noise correlation matrices to interpret ocean ambient noise.

Oceanic ambient noise is a dynamic mixture of biologic, geophysical, and anthropogenic sound sources. A goal of research is to put some order in this cacophony of information, understand the received spectral content and determine the primary contributors to the ambient noise. This paper compares three methods to assist in that process (with emphasis on noise correlation techniques): noise correlation matrices, manual selection of noise spectra, and principal component analysis.

Global examination of the wind-dependence of very low frequency underwater ambient noise.

Ocean surface winds play a key role in underwater ambient noise generation. One particular frequency band of interest is the infrasonic or very low frequency (VLF) band from 1 to 20 Hz. In this spectral band, wind generated ocean surface waves interact non-linearly to produce acoustic waves, which couple into the seafloor to generate microseisms, as explained by the theory developed by Longuet-Higgins.

Decadal trends in Indian Ocean ambient sound.

The increase of ocean noise documented in the North Pacific has sparked concern on whether the observed increases are a global or regional phenomenon. This work provides evidence of low frequency sound increases in the Indian Ocean. A decade (2002-2012) of recordings made off the island of Diego Garcia, UK in the Indian Ocean was parsed into time series according to frequency band and sound level.

Consistency in statistical moments as a test for bubble cloud clustering.

Frequency dependent measurements of attenuation and/or sound speed through clouds of gas bubbles in liquids are often inverted to find the bubble size distribution and the void fraction of gas. The inversions are often done using an effective medium theory as a forward model under the assumption that the bubble positions are Poisson distributed (i.e.

Divergence of a stereotyped call in northern resident killer whales.

Northern resident killer whale pods (Orcinus orca) have distinctive stereotyped pulsed call repertoires that can be used to distinguish groups acoustically. Repertoires are generally stable, with the same call types comprising the repertoire of a given pod over a period of years to decades. Previous studies have shown that some discrete pulsed calls can be subdivided into variants or subtypes.

St. Lawrence blue whale vocalizations revisited: characterization of calls detected from 1998 to 2001.

From 1998 to 2001, 115 h of acoustic recordings were made in the presence of the well-studied St. Lawrence population of blue whales, using a calibrated omnidirectional hydrophone [flat (+/- 3 dB) response from 5 to 800 Hz] suspended at 50 m depth from a surface isolation buoy. The primary field site for this study was the estuary region of the St.

On the relationship between signal bandwidth and frequency correlation for ocean surface forward scattered signals.

The relationship between the bandwidth of a signal and the correlation of that signal with its ocean surface reflected arrival, a quantity we term frequency correlation, has been investigated experimentally and compared with two theories. Decorrelation of wideband surface scattered signals is a direct consequence of time spread. The acoustic measurement utilized a very short pure tone signal, from which time spread has been estimated, and four broadband signals with different bandwidths, for which correlation with the transmitted signal has been measured.