Use Of Hydrophones Research Articles

Floors of Heaven: A case study of an underwater acoustic soundscape for recreational purposes

This paper presents a case study of an underwater music piece titled “Floors of Heaven” by British artist Leon Vynehall. This installation was delivered in a swimming pool as part of the Mona Foma 2023 festival, representing an example of the use of soundscapes as a means of artistic expression. The study delves into contemporary trends in soundscapes, with a focus on their utilization as a recreational tool, as the writers observe the growing interest in creating immersive and experiential art installations that engage the viewer on a sensory and emotional level. Subsequently, the paper discusses how soundscapes can be delivered in underwater environments, which present unique challenges in terms of acoustics, sound propagation, and environmental risk factors such as hearing damage. The technical considerations involved in creating an underwater sound installation, including the use of hydrophones and underwater speakers, and the importance of selecting appropriate hardware to achieve acceptable noise levels underwater, are thoroughly described. The case study of “Floors of Heaven,” which uses a combination of field recordings and synthesized sounds to explore themes of ecological collapse and the impact of human activity on underwater environments, is then presented.

Beam characterization of a custom, handheld focused ultrasound system using thermochromic liquid crystal films

AbstractFocused Ultrasound (FUS) continues to gain acceptance in the clinical realm for its ability to provide effective, non‐invasive therapeutic treatments to almost any region of the body for a host of ablative and non‐ablative applications. The development of FUS devices and their implementation requires reliable characterization and quality assurance methods to verify acoustic pressure fields and focal region characteristics. The use of hydrophones is a conventional technique for mapping the acoustic field in 3 dimensions to provide focal dimensions and location. Hydrophones, however, are expensive and may be damaged even at relatively low acoustic amplitudes. Data collection with these devices can also be labor intensive and difficult to accurately reproduce. We present preliminary findings for the development of an alternative characterization process for FUS transducers that is relatively inexpensive and time efficient. Thermochromic liquid crystal (TLC) film sensors exploit the thermochromic effect, in which exposure to specific temperature changes cause a visible change in colour. The method was tested on a portable FUS system developed in‐house for FUS‐based therapeutic applications, comprised of a 3.57 MHz FUS transducer, and a custom‐fabricated coupling cone. The results demonstrated that this method using TLC films was able to accurately provide dimensions of the focal zone and its position relative to the transducer hardware. Numerical simulations were performed along with acoustic hydrophone measurements to corroborate this data, which were found to be in general agreement. With future refinements, this cost‐effective method could be practical as an expedient and cost‐effective characterization technique for in‐house FUS transducer development.

Seismic on floating ice: data acquisition versus flexural wave noise

ABSTRACTGeophysical surveying of the Arctic will become increasingly important in future prospecting and monitoring of the terrestrial and adjacent areas in this hemisphere. Seismic data acquired on floating ice are hampered with extensive noise due to ice vibrations related to highly dispersive ice flexural waves generated by the seismic source. Several experiments have been conducted on floating ice in van Mijenfjorden in Svalbard in the Norwegian Arctic to specifically analyse the extent of flexural waves recorded with various seismic receivers and sources deployed both on top of ice and in the water below. The data show that flexural waves are severely damped at 5 m or deeper below the ice and hydrophone data suffer less from these vibrations compared with data recorded on the ice. Aliasing of single receiver hydrophone data can to some extent be suppressed using an in‐line line source of detonating cord. Experiments on ice on shallow water show prominent guided wave modes often referred to as Scholte waves propagating along the seabed. In this case, both flexural and Scholte waves interfere and make a complicated pattern of coherent noise. On shallow water, the positioning and type of the seismic source must be evaluated with respect to the coherent noise generated by these waves. Geophone strings of 25 m effectively suppress both flexural and Scholte waves due to their relative short wavelengths. An airgun generates relative more low‐frequency energy than a surface source of detonating cord. Accordingly, seismic mapping of deep seismic horizons seem to be best achieved using geophone strings of such length and an airgun source. For shallow targets, the use of hydrophones in combination with detonating cord is an appropriate solution. Seismic surveying in the Arctic always have to follow environmental restrictions of not disturbing or harming wildlife and not causing permanent footprints into the vulnerable tundra, which implies that the choice of seismic acquisition strategy might occur as a trade‐off between optimum data quality and environmental constraints.

An estimate of bedload discharge in rivers with passive acoustic measurements: Towards a generalized calibration curve?

Bedload Self-Generated Noise (SGN) measurements consist in deploying an underwater microphone (i.e. a hydrophone) in the river and to record the ambient noise. The use of hydrophones to measure bedload characteristics (flux, spatial distribution, granulometry) could be of interest as it can be more easily and rapidly deployed than physical samplers in rivers. Several measurement campaigns where conducted during spring and summer 2017 in 5 alpine rivers with contrasted transport conditions (bedload D50 between 1 and 40 mm) and varying slopes (0.05 to 1 %). Physical sampling measurements were done from a bridge along the river cross section for specific bedload flux varying between 10 and 150 g.m-1s-1. Bedload SGN measurements were obtained with a small board equipped with a hydrophone and deriving downstream the bridge within a 10 to 50 m long river section. For 2 of the 5 rivers, acoustic Doppler current profilers (ADCP) were also deployed along the river cross-section to provide a surrogate measurement of apparent bedload velocity. As a result, we have been able to draw an acoustic 1D-map of the river bottom, derived from the SGN sub-surface measurements obtained with the deriving board. The results show a coherent relation between the riverbed acoustic maps and the physical samplings for 3 rivers over 5. Bedload profile were less consistent with SGN measurements when bedload transport was localized in a narrow channel. The apparent bedload velocities obtained with ADCP for 2 rivers are consitent with the physical samplings (bedload location and flux distribution) but a slight bias was observed and is attributed to grain-size sorting effects along the cross-section. Finally, when plotting together 4 over 5 rivers, an almost linear relation can be established between bedload discharge (computed with physical samplings data) and the average acoustic response (i.e acoustic power averaged over the cross-section). This result suggests that a generalized calibration curve could exist between bedload SGN and bedload discharge. The existence of an outsider is interpreted as a problem related to propagation effects. Further researches should therefore concentrate their effort on deconvoluting SGN signals from propagation effects to give a better confident proxy for bedload discharge measurement in different rivers types.

Measuring bedload grain-size distributions with passive acoustic measurements

Bedload Self-Generated Noise (SGN) measurements consist in deploying an underwater microphone (i.e. a hydrophone) in the water course and to record the ambient noise of a river. The use of hydrophones is of interest as it can be easily deployed and can provide a continuous monitoring of bedload transport. However, developments are still required to fully understand how bedload characteristics (e.g. specific flux or granulometry) are related to bedload SGN parameters (e.g. acoustic power and spectrum). Laboratory experiments have shown that central and peak frequencies of bedload noise decrease as the particle size increases, just like in string instruments where the tone frequency decreases from a narrow string to a broader string. In this paper, we propose to test a new inverse method enabling the estimation of bedload grain size distributions from SGN measurements. The inverse method is based on a theoretical modelling of the noise generated by a bedload mixture. SGN and physical sampling measurements have been made in 5 French alpine rivers having several transport conditions (bedload D50 from 1 to 40 mm) and varying slopes (0.05 to 1%). Measurements were made for specific bedload flux varying from 10 to 150 g.m-1s-1. The proposed inverse method was used to estimate the bedload grain size distributions. SGN results are compared to bedload samples and are found to largely overestimate sampled granulometries. Finally, it is observed that the spectral characteristics of bedload SGN are not related to bedload GSD but rather to the roughness of the river bed, acting as a source of attenuation and shaping bedload SGN spectra.

Soundpeaking – Hydropeaking induced changes in river soundscapes

AbstractUnderwater soundscapes and their unique acoustic signatures are mainly generated through movement of streambed sediment, subsequent particle collisions, and turbulence created by water flowing over submerged obstructions such as rocks and woody debris. This study characterized river soundscapes in Alpine rivers of Trentino, (North East Italy) with the combined use of hydrophones and a new microelectricalmechanical systems based device (Hydroflown) that is capable of measuring particle velocity components of the sound field. Pool and riffle habitats affected and unaffected by hydropeaking were characterized in terms of their particle velocity and sound pressure levels across 10 octave bands (acoustic signature) to assess temporal variations in overall sound levels, changes in frequency composition, and relationship to hydromorphological habitat parameters. Data revealed that soundscapes affected by hydropeaking are highly homogenized, and sound pressure levels are strongly correlated with turbine discharge, which results in rapid, multiple‐fold spikes in low frequency amplitude levels within the typical hearing range of common teleost fish species. The outcomes of this study provide the basis for further examination of the resulting behavioural and physiological responses of organisms to anthropogenic changes in river soundscapes.

Passive acoustic monitoring of bed load discharge in a large gravel bed river

AbstractSurrogate technologies to monitor bed load discharge have been developed to supplement and ultimately take over traditional direct methods. Our research deals with passive acoustic monitoring of bed load flux using a hydrophone continuously deployed near a river bed. This passive acoustic technology senses any acoustic waves propagated in the river environment and particularly the sound due to interparticle collisions emitted during bed load movement. A data set has been acquired in the large Alpine gravel‐bedded Drau River. Analysis of the short‐term frequency response of acoustic signals allows us to determine the origin of recorded noises and to consider their frequency variations. Results are compared with ancillary field data of water depth and bed load transport inferred from the signals of a geophone array. Hydrophone and geophone signals are well correlated. Thanks to the large network of deployed geophones, analysis of the spatial resolution of hydrophone measurements shows that the sensor is sensitive to bed load motion not only locally but over distances of 5–10 m (10–20% of river width). Our results are promising in terms of the potential use of hydrophones for monitoring bed load transport in large gravel bed rivers: acoustic signals represent a large river bed area, rather than being local; hydrophones can be installed in large floods; they can be deployed at a low cost and provide continuous monitoring at high temporal resolution.

Deployment of a Remote Acoustic Monitoring System for Pipeline-Asset Integrity

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 171763, “Field Deployment of an Innovative Acoustic Monitoring System for Remote Real-Time Pipeline-Asset Integrity,” by R. Schiavon, Tecnomare; G. Bernasconi, Politecnico di Milano; G. Giunta and G.P. Borghi, Eni; and N. Okere, NAOC, prepared for the 2014 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 10–13 November. The paper has not been peer reviewed. Since 2007, an operator in Nigeria has registered a significant increase of oil-spill events caused by sabotage and oil-theft activities. The risks for personnel safety and environmental protection were such that it was decided to investigate new detection and monitoring systems. The technology presented here allows detecting and locating leaks taking place at a distance from the sensor of up to 35 km. Introduction The technology of this system is based upon discrete vibroacoustic sensing. This technology takes advantage of the fact that any acoustic signal reaching, or generated upon, the pipeline will introduce vibroacoustic waves within the pipeline body and the transported-fluid medium (crude oil, brine, and natural gas). In addition to the general noise of the fluid flow within the pipeline, these acoustic waves are transported along the conduit for long distances. Especially within the fluid, the sound propagation is expected to travel several kilometers, depending on the density of the medium and the pipe diameter. In the pipe body, because of the variability of the boundary conditions, the calculation of the sound propagation is complex, but mathematical analyses proved the existence of modal solutions that are allowed to travel several kilometers. Moreover, for high- density fluids (i.e., crude oil or brine), the acoustic waves can be measured across the pipe shell. Vibroacoustic monitoring implies the recording of the low-frequency elastic waves traveling along the pipe body by use of accelerometers and geophones, and of the pressure wave traveling into the fluid by use of hydrophones. When the sensors are placed on both sides of a source point, cross-correlation techniques enable the localization of the origin point. If only one recording point is available, it is possible to take advantage of the different propagation velocity of the acoustic waves in the pipe shell and in the inner fluid.

Boiling bubbles monitoring for the protection of the LIPAc beam-dump

Local boiling in the cooling water of the LIPAc beam dump is an indication of abnormal conditions and will be used to trigger a fast beam shutdown through the Machine Protection System before any mechanical damage occurs. A prompt detection of boiling can be done thanks to the use of hydrophones recording the boiling sound. The sensors must have a broad and flat frequency range as well as a high sensitivity. In order to study the characteristics of the sound produced by localized boiling in different situations, an experiment has been carried out on a 1:1 prototype of the beam dump. A hydrophone was placed inside the cooling loop and the sounds produced by the bubbles were recorded. The heating was provided by means of an isolated “hot finger” giving up to 300W/cm2 of controlled localized power density. The experimental setup allows the characterization of the time-spectral content for different cooling flows, which is required for the design of the final protection subsystem.

Hydrophone VSP surveys in hard rock

Seismic imaging in hard rock environments is gaining wider acceptance as an exploration technique and as a mine-planning tool. To date, 13 successful case studies have been acquired in Australia. The images generated from hard rock targets exhibit large levels of complexity and their interpretations remain an active area of study. To assist the imaging and better understand the source of the reflections observed, vertical seismic profiling (VSP) can be employed. This technique is not readily applied to hard rock environments because cost and operational issues often prove prohibitive. We propose the use of hydrophone arrays as a cost effective solution to VSP acquisition. We highlight the key challenges in using these receivers and propose solutions to overcome them. By careful acquisition methodologies and refined signal processing techniques, the tube waves that have up to now compromised the use of hydrophones for VSP acquisition can be effectively mitigated. We show that the data acquired with hydrophones compare favorably to that acquired with conventional 3C geophones. The data acquired with hydrophones come at a fraction of the cost and deployment time required for conventional acquisition procedures. Our results show that hydrophone vertical seismic acquisition is a viable, cost effective, and efficient solution that should be employed more routinely in hard rock environments to enhance the value of the surface data sets being acquired.

Long-term evaluation of scientific-echosounder performance

Abstract Knudsen, H. P. 2009. Long-term evaluation of scientific-echosounder performance. – ICES Journal of Marine Science, 66: 1335–1340. When scientific acoustic instruments are utilized for quantitative measurements of underwater biological resources, it is extremely important to know their overall performance, and it is imperative to measure their stability over time. Echosounders mounted on research vessels are therefore routinely calibrated several times annually, often immediately before, during, and after important resource-assessment surveys. In recent years, multifrequency systems for acoustic surveys requiring species identification and categorization based on the frequency response of targets have been introduced, further emphasizing the importance of monitoring instrument performance. In the 1970s, hydrophones and steel spheres were used as alternative references for calibrations. Substantial variations of system performance were observed, however, and gradually it was accepted that the use of hydrophones was inappropriate, because their performance varied more than that of the instruments being calibrated. Not until optimized reference targets were introduced in ca. 1980, was it possible to monitor the stability of acoustic-survey equipment with an acceptable degree of confidence. For the first time, the true, long-term stability of transducers, including ageing effects, could be accurately measured. This paper gives examples of calibration time-series for several Norwegian research vessels operating in various regions from Arctic to tropical waters.

Acoustic monitoring of prestressed concrete pipe

The Bureau of Reclamation has made extensive use of Prestressed Concrete Pipe (PCP) in several of its major water projects. Widespread corrosion and failure of the reinforcing wire on over 6 miles of PCP used for the Central Arizona Project was found in 1990. This pipe had been in service less than 15 years which is significantly shorter than its expected design life. It was apparent that if wires continued to fail, catastrophic rupture of the pipe would result. Repair methods were developed to restore the prestressing forces to a deteriorated pipe section. This would extend its service life; however, locating the deteriorated areas in a buried pipeline was difficult. Numerous technologies were tested inside and outside the pipe in attempts to locate the distressed areas. None of the techniques tested could reliably locate areas of distress, however, one method has shown great promise. The use of hydrophones (underwater microphones) to detect the sound caused by the failure and subsequent slippage of the reinforcing wire has been demonstrated to be quite effective. The development of this technology is described, from initial field testing using a single pair of hydrophones, to the system currently being used for the continuous monitoring of a 2-mile pipeline. This system uses an array of 12 hydrophones and a sophisticated computer system to detect sounds in the pipeline, classify them as either wire-related sounds or extraneous sounds, and, based on the location of the wire-related sounds, map areas of pipe deterioration.

Progress toward quantitative local ultrasonic measurements

The major part of experimental studies in ultrasonics deals with relative measurements of the acoustic field. It means that the absolute value of the ultrasonic pressure or of the acoustic displacements is unknown. Nevertheless, various methods exist for measuring the pressure in a fluid: use of hydrophones, reflection measurements and use of the inverse return principle, calorimetry, ultrasonic balance, etc. In most cases, they are quite difficult to handle, they induce some perturbation of the acoustic field to be measured, and, usually, give only a mean value of this field. The development of laser ultrasonics recently opened new perspectives in this domain. Laser probing of acoustic surface displacements gives very accurate local quantitative measurements. Such probing was limited to interfaces where the laser beam was reflected. This capability was recently extended to measurements of acoustic pressures inside fluids and acoustic dilatation inside solids [X. Jia, Ch. Matteï, and G. Quentin, J. Appl. Phys. 77, 5528–5537 (1995)]. This paper describes the method used and emphasizes the usefulness of such quantitative local ultrasonic measurements and its field of applications.

An overview of the AIUM/NEMA standard and the draft IEC standard for ultrasound exposure measurements

<h2>Abstract</h2> The objectives of the AIUM/NEMA safety standard and the IEC draft are similar and intended to ensure that sufficient information regarding output of diagnostic ultrasound instruments is available so that users can make informed judgements regarding equipment uses. The objectives of the IEC draft standard are to <ul><li>1.(i) define a group of acoustic parameters which can be measured on a physically practical basis (hydrophones);</li><li>2.(ii) define a second group of parameters which can be derived under certain assumptions from these measurements and called derived intensity parameters;</li><li>3.(iii) define a measurement procedure which may be used for the determination of acoustic pressure parameters;</li><li>4.(iv) define the conditions under which the measurements of acoustic parameters can be made in the frequency range 0.5–15 MHz using calibrated piezoelectric hydrophones. Although a group of exposure parameters has been identified, the IEC does not recommend which is the most relevant for field characterisation.</li></ul> The difference between standards is largely a result of uncertainties in the use of hydrophones at the time of formulating the AIUM/NEMA standard. With the advent of modern high quality PVDF miniature hydrophones the more recent IEC Draft Standard recommends specification of the acoustic field in terms of acoustic pressure which is directly measured with a hydrophone. The IEC also differs from the AIUM/NEMA standard for acoustic labelling, where the quantity measured by miniature hydrophones is defined as acoustic pressure and prefers not to use intensity which is derived from plane wave approximation.

Composite piezoelectric sensors

A hydrophone is an underwater microphone or transducer used to detect underwater sound. The sensitivity of a hydrophone is determined by the voltage that is produced by a hydrostatic pressure wave. The hydrostatic voltage coefficient, gh, relates the electric field appearing across a transducer to the applied hydrostatic stress, and is therefore a useful parameter for evaluating piezoelectric materials for use in hydrophones. Another piezoelectric coefficient frequently used is the hydrostatic strain coefficient, dh, which describes the polarization resulting from a change in hydrostatic stress. The gh coefficient is related to the dh coefficient by the relative permittivity (K): gh = dh/ɛoK, where ɛo is the permittivity of free space.

Laser-induced acoustic waves in water

Acoustic waves in water may be produced by the absorption of infrared energy from a pulsed laser. The temperature distribution in water for a kilowatt pulse with a duration of the order of a millisecond can be described in terms of the beam parameters and the optical absorption coefficient of water. The expression for the temperature distribution has been solved numerically. The acoustic waves were studied by the use of hydrophones in an anechoic tank filled with tap water. Cylindrical waves with exponentially decreasing amplitudes with depth were produced by the absorption of laser radiation. The velocity of these waves was in close agreement with the velocity of acoustic waves in water.

Characteristics of continuously tunable diaphragms

By the use of hydrophones fitted with tunable diaphragms it is now possible to develop submarine signalling along somewhat the same lines as in radio-telegraphy. It may be expected that considerable advantages will accrue from the use of transmitters giving pure notes over considerable ranges of frequencies, as narrow bands of given frequency may now be picked up to the exclusion of others. Furthermore by tuning in, the hydrophone is used at its maximum sensitiveness consistent with proper damping, so that it may be possible to receive over considerable distances without the use of valve amplifiers. As submarine signals offer a promising method of assisting navigation and, in combination with radio-telegraphy, of determining distance from lighthouses or light-ships, the possibility of dispensing with such refinements as valve amplifiers may be considered advantageous from the point of view of the navigator of a vessel not equipped with the usual ship's wireless.