A sound projector for acoustic tomography and global ocean monitoring

Multimegameter-range acoustic data obtained by bottom-mounted receivers show significant acoustic energy penetrating several hundred meters into geometric shadow zones below cusps (caustics) of timefronts computed using climatological databases [B. D. Dushaw et al., IEEE J. Ocean. Eng. 24, 202-214 (1999)]. This penetration is much larger than predicted by diffraction theory. Because these receivers are horizontal arrays, they do not provide information on the vertical structure of the shadow-zone arrivals. Acoustic data from two vertical line array receivers deployed in close proximity in the North Pacific Ocean, together virtually spanning the water column, show the vertical structure of the shadow-zone arrivals for transmissions from broadband 250-Hz sources moored at the sound-channel axis (750 m) and slightly above the surface conjugate depth (3000 m) at ranges of 500 and 1000 km. Comparisons to parabolic equation simulations for sound-speed fields that do not include significant internal-wave variability show that early branches of the measured timefronts consistently penetrate as much as 500-800 m deeper into the water column than predicted. Subsequent parabolic equation simulations incorporating sound-speed fluctuations consistent with the Garrett-Munk internal-wave spectrum at full strength accurately predict the observed energy level to within 3-4-dB rms over the depth range of the shadow-zone arrivals.

Section: Methodsmentioning

confidence: 99%

The vertical structure of shadow-zone arrivals at long range in the ocean

Uffelen

Worcester

Dzieciuch

et al. 2009

“…The model is based on the similarity of mechanical differential equations and equations for ordinary electrical elements, such as capacitors, inductors, resistors, and transformers. 20 The model is simpler than the finite element analysis, 20 and it does not need special software or powerful computers to facilitate the prediction of precise projector parameters. This model was continuously compared with experimental data from the actual projector test.…”

Section: Tunable Resonator Tubementioning

confidence: 99%

“…During manufacture, the wall thickness was changed from 0.0095 m, as was used during simulation, to 0.0125 m. As a result, the resonance frequency increased to 25 Hz and sources were sweeping from 225 to 325 Hz. The prototype source manufactured with a 0.0095 m wall 20 swept in the expected 200-300-Hz frequency band. Unfortunately, the first prototype used an actuator with a very low rate, which did not allow testing of high-rate frequency sweeping.…”

Section: Experimental Testing Of Tunable Organ Pipesmentioning

confidence: 99%

“…A simple and practical model of a tunable organ pipe 20 will be used further for simulation of the frequency and time responses of a tunable organ-pipe source. This paper's objective is to consider general aspects of tunable resonant sound-source theory and to provide detailed analysis of time-response processes in the practical design of a real tunable organ pipe.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Underwater tunable organ-pipe sound source

Morozov

Webb

2007

A highly efficient frequency-controlled sound source based on a tunable high-Q underwater acoustic resonator is described. The required spectrum width was achieved by transmitting a linear frequency-modulated signal and simultaneously tuning the resonance frequency, keeping the sound source in resonance at the instantaneous frequency of the signal transmitted. Such sound sources have applications in ocean-acoustic tomography and deep-penetration seismic tomography. Mathematical analysis and numerical simulation show the Helmholtz resonator's ability for instant resonant frequency switching and quick adjustment of its resonant frequency to the instantaneous frequency signal. The concept of a quick frequency adjustment filter is considered. The discussion includes the simplest lumped resonant source as well as the complicated distributed system of a tunable organ pipe. A numerical model of the tunable organ pipe is shown to have a form similar to a transmission line segment. This provides a general form for the principal results, which can be applied to tunable resonators of a different physical nature. The numerical simulation shows that the "state-switched" concept also works in the high-Q tunable organ pipe, and the speed of frequency sweeping in a high-Q tunable organ pipe is analyzed. The simulation results were applied to a projector design for ocean-acoustic tomography.

“…Ideally, these alternative sound sources should be capable of producing a signal that maintains the wide bandwidth of explosive charges with reduced amplitude to satisfy environmental concerns. Sound sources such as low frequency shakers [5] and resonators [6] have been developed, but often do not have the bandwidth, convenience, and efficiency of explosive charges. A number of other sources are described in Dobrin [7], but the CSS differs from all of these, and is more similar to an explosive source in the following manner: The CSS generates pressure directly in the water, and no energy is lost through motion of an elastic membrane, as in the Aquapulse (trademark of Western Geophysical Co.) or through the motion of any mechanical piston or valve as in sparkers or boomers [7].…”

Section: Introductionmentioning

confidence: 99%

An investigation of the combustive sound source.

McNeese

Sagers

Wilson

et al. 2010

The combustive sound source (CSS) is a versatile impulsive underwater sound source with an adjustable bandwidth and output amplitude. Unlike typical impulsive acoustic sources, CSS can maintain a wide bandwidth at low amplitude; hence, it is a more environmentally friendly impulsive source for ocean acoustics experiments and surveys. The CSS consists of a submersible combustion chamber, open to the water, which is filled with a combustible fuel/oxidizer mixture. The mixture is ignited and a combustion wave propagates through the mixture. During this process the ensuing bubble expands due to an increase in temperature and can collapse to a smaller volume than before ignition. This bubble activity radiates acoustic pulses. The CSS can be used as a source for low-frequency sediment characterization and TL measurements, and when deployed on the bottom can produce seismic interface waves. In addition to stationary deployments in the water column, CSS can be deployed in a tow body and as an array. Discussion will focus on the latest CSS design including functionality, acoustic output, long-term operational stability, and future development plans.