Robustness and constraints of ambient noise inversion

This paper applies Bayesian inversion to bottom-loss data derived from wind-driven ambient noise measurements from a vertical line array to quantify the information content constraining seabed geoacoustic parameters. The inversion utilizes a previously proposed ray-based representation of the ambient noise field as a forward model for fast computations of bottom loss data for a layered seabed. This model considers the effect of the array's finite aperture in the estimation of bottom loss and is extended to include the wind speed as the driving mechanism for the ambient noise field. The strength of this field relative to other unwanted noise mechanisms defines a signal-to-noise ratio, which is included in the inversion as a frequency-dependent parameter. The wind speed is found to have a strong impact on the resolution of seabed geoacoustic parameters as quantified by marginal probability distributions from Bayesian inversion of simulated data. The inversion method is also applied to experimental data collected at a moored vertical array during the MAPEX 2000 experiment, and the results are compared to those from previous active-source inversions and to core measurements at a nearby site.

Section: Forward Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Bayesian geoacoustic inversion using wind-driven ambient noise

Quijano

Dosso

Dettmer

et al. 2012

“…Marine ambient noise generated at the surface by breaking waves, wind, and rain has received increased interest lately as an acoustic source, allowing the development of passive techniques for surveying the sea bottom, such as Harrison and Simons' technique for bottom-loss estimation [5][6][7][8][9][10] (and its extension to the investigation of bottom layering 11,12 ) and the passive fathometer. [13][14][15][16][17] Harrison and Simons' technique produces an estimate of the bottom loss, as a function of frequency and grazing angle, by beamforming ambient-noise data collected by a vertical line array of hydrophones.…”

Section: Introductionmentioning

confidence: 99%

High-resolution bottom-loss estimation using the ambient-noise vertical coherence function

Muzi

Siderius

Quijano

et al. 2015

The seabed reflection loss (shortly "bottom loss") is an important quantity for predicting transmission loss in the ocean. A recent passive technique for estimating the bottom loss as a function of frequency and grazing angle exploits marine ambient noise (originating at the surface from breaking waves, wind, and rain) as an acoustic source. Conventional beamforming of the noise field at a vertical line array of hydrophones is a fundamental step in this technique, and the beamformer resolution in grazing angle affects the quality of the estimated bottom loss. Implementation of this technique with short arrays can be hindered by their inherently poor angular resolution. This paper presents a derivation of the bottom reflection coefficient from the ambient-noise spatial coherence function, and a technique based on this derivation for obtaining higher angular resolution bottom-loss estimates. The technique, which exploits the (approximate) spatial stationarity of the ambient-noise spatial coherence function, is demonstrated on both simulated and experimental data.

“…[9][10][11][12] The possibility of dispensing with active sound sources makes the technique particularly attractive, because of the reduced environmental impact, equipment complexity, and power consumption. 10,13 However, the technique can produce inaccurate results in conditions of low wind and/or waves, 14 and whenever the natural-noise field is contaminated by an interferer, such as the engine of a nearby ship. 15 It is shown in this study that ships can actually be used as sources of opportunity, to obtain passive estimates of the bottom reflection loss with Harrison and Simons's technique.…”

Section: Introductionmentioning

confidence: 99%

Passive bottom reflection-loss estimation using ship noise and a vertical line array

Muzi

Siderius

2017

An existing technique for passive bottom-loss estimation from natural marine surface noise (generated by waves and wind) is adapted to use noise generated by ships. The original approach-based on beamforming of the noise field recorded by a vertical line array of hydrophones-is retained; however, additional processing is needed in order for the field generated by a passing ship to show features that are similar to those of the natural surface-noise field. A necessary requisite is that the ship position, relative to the array, varies over as wide a range of steering angles as possible, ideally passing directly over the array to ensure coverage of the steepest angles. The methodology is illustrated through simulation and applied to data from a field experiment conducted offshore of San Diego, CA in 2009.