27 research outputs found
Waterfalls in space, and other problems of "underwater" acoustics on a small planet
No full textWhilst extraterrestrial liquids do occur in the Solar System, today's acoustical oceanographers have fewer sites to which they can apply their experience of Earth's oceans than perhaps they would have had in the early Solar System, with its magma oceans. Possible sites are Saturn's moons Titan and Enceladus, and Jupiter's moon Europa. The ability to transfer our understanding of Earth's acoustical oceanography to other moons and planets is particularly valuable, given that current understanding is sufficient to undertake complex inversions to estimate Earth's ocean environmental parameters from relatively sparse, or even naturally-occurring, acoustical signals. However such transference should be done with care, as terms familiar in Earth's acoustical oceanography may not be correct on other worlds. For example, in a deep ocean on a small world (such as Europa), the hydrostatic pressure will not equal the product of the density, the depth, and the surface value of the acceleration due to gravity, since the latter can vary with depth, and because vertical lines are not parallel on a small planet. This paper explores two cases of transferring our terrestrial experience off world, to the ice seas of Europa, and to the methane lakes and waterfalls of Titan. ©2008 Acoustical Society of Americ
The problems with acoustics on a small planet
No full textIn recent years increased attention has been paid to the potential uses of acoustics for extraterrestrial exploration. This paper concerns two aspects which should be taken into account when transposing terrestrial experience with acoustics to smaller worlds. These are, specifically, the effect on the acoustics of the variation of gravity with depth, and the curvature of the world's surface. A case resembling Europa is used quantitatively to illustrate these effects, indicating significant errors if these factors are neglected
Cavitación y cetáceos. [Cavitation and cetacean]
No full textBubbles are the most acoustically active naturally occurring
entities in the ocean, and cetaceans are the most
intelligent. Having evolved over tens of millions of years
to cope with the underwater acoustic environment,
cetaceans may have developed techniques from which we
could learn. This paper outlines some of the possible interactions,
ranging from the exploitation of acoustics in
bubble nets to trap prey, to techniques for echolocating in
bubbly water, to the possibility that man-made sonar signals
could be responsible for bubble generation and death
within cetaceans.ResumenLas burbujas son las entidades naturales del océano más activas acústicamente, y los cetáceos las más inteligentes. Tras decenas de millones de años de evolución para adaptarse al entorno acústico submarino, los cetáceos pueden haber desarrollado una serie de técnicas de las que bien podríamos aprender.Este artículo pone de relieve algunas posibles interacciones, que van desde la explotación de la acústica en redes de burbujas utilizadas como trampas para presas, hasta técnicas para la ¿ecolocación¿ en aguas burbujeantes, o la posibilidad de que las señales sonares provocadas por el hombre sean responsables de la generación de burbujas y de muerte de cetáceos
The sounds of seas in space
No full textOn 14 January 2005 the Huygens space probe landed on Titan, the surface of which had previously been obscured by smog. This exercise was undertaken prior to the probe’s successful landing, in an attempt to calculate the sounds which would be associated with splashdowns and methane-falls, in the hypothetical scenario that (of the many sensing systems on Huygens) only the acoustic information was available in order to interpret conditions on Titan. The exercise includes innovations in the inversion of bubble entrainment noise to estimate bubble populations, and illustrates the benefits of using acoustics for space exploration
Wake penetrating sonar
No full textThis paper describes a sonar which can operate in bubbly water. It is here deployed to penetrate the wake of a ship of 3,953 gross register tonnage. Orthodox Cold War sonar technology is not optimized for the shallow coastal waters that typify many current operations. The United States use dolphins in such waters, and the Twin Inverted Pulse Sonar (TWIPS) described here arose as a demonstration that echolocation was possible in bubbly water in response to a video showing dolphins generating bubble nets when hunting: if echolocation were impossible in these nets, then during this hunt the dolphins would have compromised their sonar. In this paper TWIPS detects and classifies targets against clutter by distinguishing between linear and nonlinear scatterer. For other applications, it has the potential to distinguish those nonlinear targets which scatter energy at the even-powered harmonics from those which scatter in the odd-powered harmonics. TWIPS can also, in some manifestations, require no range correction (and therefore does not require the a priori environment knowledge necessary for many remote detection technologies). The method applies to a range of sensors, including the use of radar to distinguish between circuitry, metal and soil; the use of LIDAR to detect combustion products; and MRI
Cetacean acoustics in bubbly water (Invited Paper)
No full textMarine mammal signals often propagate through bubbly water, be they generated under breaking waves, wakes, or even by the mammals themselves. Two circumstances are of particular interest: the possible use of acoustic signals to trap prey in bubble nets; and the ability of dolphin sonar to operate in bubbly water (such as the surf zone) that would confound the best human sonar, despite the fact that the dolphins possess ‘hardware’ which is comparatively mediocre. This paper examines these circumstances
Hypotheses regarding exploitation of bubble acoustics by cetaceans
No full textBubbles are the most acoustically active naturally occurring entities in the ocean, and cetaceans are the most intelligent. Having evolved over tens of millions of years to cope with the underwater acoustic environment, cetaceans may have developed extraordinary techniques from which we could learn. This paper outlines some of the possible interactions, ranging from the exploitation of acoustics by humpback whales (Megaptera novaeangliae) in bubble nets to trap prey, to techniques by which coastal dolphins (e.g. of the genus Cephalorhynchus) could successfully echolocate in bubbly water (a hypothesis which has led to the development of a man-made sonar which can penetrate bubble clouds, and a range of possibilities for homeland security). ©2008 Acoustical Society of America<br/
Verification of an image calibration method in ultrasound contrast agent imaging on a perfusion phantom
No full textAcoustic sensing of renal stone fragmentation in extracorporeal shockwave lithotripsy
No full textThis thesis describes the research carried out by the author on the exploitation of acoustic emissions
detected during extracorporeal shockwave lithotripsy (a non-invasive procedure for the treatment of
urinary stones) to develop a new diagnostic system. The work formed part of a research project on
lithotripsy undertaken by the University of Southampton in collaboration with Guy's and St Thomas'
NHS Foundation Trust (London) and a UK based company, Precision Acoustics Ltd (Dorchester). It
takes to a clinical conclusion the proposition made by Leighton and Coleman in 1992 that it might be
possible to build a sensor which would automatically exploit these passive acoustic emissions to
monitor the efficacy of a lithotripsy treatment. The work, predominantly experimental, involved both
in vitro and in vivo investigations. In particular, a first prototype diagnostic system (i.e. sensor plus
analysis software) was developed and tested in vitro during trials which included the use of a novel
cavitation sensor (on loan from the National Physical Laboratory, Teddington) and stone phantoms
designed by the author. This initial system was, then, refined and tested during clinical trials that
involved 130 patients. A preliminary trial on 51 patients aimed at refining the system and gathering
knowledge on the features of emissions recorded in vivo to produce an on-line monitoring system.
This trial was followed by other two trials that compared the output of the on-line acoustic system
against the ‘gold standard’ X-Ray assessment of treatments outcomes. The former of these two trials
involved 30 patients, and empirically defined the values of the key parameters (identified during the
in vitro tests) that would be used as the basis of the diagnosis. In particular, a classification rule of
treatments as being successful or unsuccessful was identified, and shown to agree significantly
(kappa=0.95) with the ‘gold standard’ follow-up assessment. The latter trial tested the final system
on 49 patients and confirmed an accurate treatment classification (kappa=0.94) in terms of the
successful/unsuccessful criterion
Bubble acoustics: from whales to other worlds
No full textGas bubbles in liquids have an extraordinary ability to interact with sound fields. They are potent generators, absorbers, and scatterers of sound, and can have a profound effect upon the sound speed (changing it on subsecond timescales by a factor of 2 or more under breaking ocean waves, for example). Bubbles generate the song of a babbling brook, and ocean sounds that help us understand the global carbon budget. Bubbles activated by ultrasound can assist industrial processing, or aid medical diagnosis and therapy. This Rayleigh Medal Lecture paper records the work I have undertaken to understand and exploit them
