Sound Speed Contrast Research Articles

Vertical distribution and acoustic characteristics of deep water micronektonic crustacean in the Bay of Biscay

Vertical distribution of meso- and bathypelagic crustacean are scarcely known. The logistics involved in their studies hinder an adequate assessment of their role in the deep ecosystems. As a result, the literature on zooplankton scattering models is mainly focused on epipelagic organisms, particularly krill species. This study analyses data of the plankton community classified by family from the surface down to 2000 m taken in the Bay of Biscay, but focusses on the meso- and bathypelagic zone. Photographic data was employed to obtain a micronektonic crustacean shape catalogue. The Distorted Wave Born Approximation (DWBA) model was employed to estimate target strength. Pasiphaeidae, Euphausiidae and Acanthephyridae were mainly distributed above 500 m depth, while Benthesicymidae, Sergestidae and Mysidae were concentrated in the lower mesopelagic to upper bathypelagic area. The most abundant species were Euphausiidae and Benthesicymidae with up to 30 and 40 individuals per cubic meter respectively. Standard length ranged from 8 to 85 mm and was significantly related with height but not with depth. The Pasiphaeidae family presented the largest individuals followed by Acanthephyridae and Sergestidae while Euphausiidae, Benthesicymidae, and Mysidae were shorter. An smooth fluid-like response was estimated for shorter organisms, while individuals of 60 mm or higher present TS oscillations from around 60 kHz. Pasiphaeidae present an almost 10 dB higher TS than Sergestidae, Acanthephyridae and Benthesicymidae while Mysidae followed by Euphausiidae produce the lower TS. Simple models of TS values at broadside versus the logarithm of standard length (SL) that can be employed as an approximation of their scattering are provided for four common frequencies (TS = 58.5*log10(SL)-188.7, TS = 57.03*log10(SL)-174.1, TS = 22.48*log10(SL)-157.14, TS = 17.55*log10(SL)-135 and TS = 10.53*log10(SL)-109 at 18, 38, 70, 120 and 200 kHz respectively). Changes in body density and sound speed contrast may increase by 10 or 2 dB the resulting TS respectively but are constant in phase, while orientation can decrease the TS by up to 20 dB at the higher frequencies and alter the spectra to an almost flat trend. This study provides further insight into the vertical distribution and physical characteristics of the micronektonic crustacean families inhabiting the Bay of Biscay down to 2000 m depth. It also estimates their echo from a real-shape catalogue that can be employed to infer knowledge from acoustic recordings, particularly of the lower mesopelagic and the bathypelagic zones.

Concurrent observations of the euphausiid Thysanoessa raschii in an Icelandic fjord by acoustics and Video Plankton Recorder: comparisons with theoretical models of target strength

Abstract In two surveys in an Icelandic fjord, September 2016 and October 2018, the target strength (TS) of the euphausiid Thysanoessa raschii was estimated at four frequencies (38, 70, 120, 200 kHz) by matching the acoustic backscatter to the number of euphausiids detected by a Video Plankton Recorder (VPR). Using forward-looking strobe lights on the VPR and doubling the towing speed lowered the estimated target strength by 4.3 dB. In 2016, the TS for euphausiids of mean length 20.7 mm averaged −98.4, −92.3, −86.6 and −82.8 dB at 38, 70, 120 and 200 kHz frequencies, respectively. In 2018, TS for euphausiids of mean length 19.9 mm averaged −98.2 dB at 38 kHz and −88.3 dB at 120 kHz. Theoretical modeling using a Distorted-Wave Born Approximation-based approach was used to compute the average target strength for the observed length distributions and for several density and sound speed contrast (g, h) and orientations. Except at 38 kHz, these results are in reasonable agreement with the TS estimated from the VPR-acoustic comparisons. The methodological approach presented provides an alternative to net-acoustic comparison or modeling for the estimation of euphausiid target strength.

Broadband measurements and modeling of low-grazing angle bottom reflections from muddy marine sediments

In 2017 and 2022, a series of experiments using explosive sound sources were conducted on the New England Mud Patch (NEMP), an area of the Eastern US Continental shelf defined by its thick muddy seafloor sediments. Broadband measurements from the near-bottom Intensity Vector Acoustic Recorders (IVARs) reveal resonant frequencies in the bottom reflected signals, which are excited at very low-grazing angles. A signal model based on a layered-bottom reflection coefficient is used to examine the geoacoustic properties of the marine mud, which leads to the conclusion that the sound-speed contrast across the water-mud interface (i.e. index of refraction, n) is less than one (n < 1), and also an increase in sound-speed occurs within the deeper mud-sediments (n > 1). Measurements in May 2022, replicating the same source and receiver locations from March 2017, also show resonances in the bottom-reflected signal. Differences between the two data sets (2017 and 2022) are primarily caused by the complex oceanography encountered during the spring-time measurements, absent during the isothermal winter conditions. Comparison of the two datasets examines the stability of the sound-speed contrast, including the effect of time-varying temperature at the water-mud interface.

Binary volume acoustic holograms

Acoustic holograms or phase conjugate acoustic lenses are a simple inexpensive method for forming complex acoustic fields. They are 3D printable phase plates that can map an incident field onto a pre-defined phase distribution such that it diffracts to form a desired field. These phase plates areanalogues of thin optical holograms with a thickness d ≅ λ the design wavelength. Another class of optical holograms are “thick” or “volume” holograms, composed of weak periodic variations in the refractive index, for which d ⪢ λ. These volume holograms are significantly more selective to the wavelength and direction of the incident field allowing for greater ability to multiplex patterns within a single hologram. In this work, we explore the generation of volume acoustic holograms using multi-material 3-D printing. First, we numerically assess the impact of sound speed contrast, absorption, and quantisation on efficiency. A greedy optimization approach is then introduced for the design of a volumetric hologram from a desired set of input/output fields. We then validate the approach experimentally using test samples printed on an Objet Connex 350. Several holograms are fabricated demonstrating both spatial and frequency multiplexing of different patterns in a single volume.

The Annual Variability of Density and Sound-Speed Contrasts and Their Influence on Target Strength of Euphausia pacifica off the Coast of Kushiro, Hokkaido

The Annual Variability of Density and Sound-Speed Contrasts and Their Influence on Target Strength of <i>Euphausia pacifica</i> off the Coast of Kushiro, Hokkaido

Accounting for seasonal and composition‐related variability in acoustic material properties in estimating copepod and krill target strength

AbstractEstimation of abundance or biomass, using acoustic techniques requires knowledge of the frequency dependent acoustic backscatter characteristics, or target strength, of organisms. Target strength of zooplankton is typically estimated from physics‐based models that involve multiple parameters, notably including the acoustic material properties (i.e., the contrasts in density and sound speed between the animal and surrounding seawater). In this work, variability in the acoustic material properties of two zooplankton species in the Gulf of Maine, the copepod (Calanus finmarchicus) and krill (Meganyctiphanes norvegica), was investigated relative to changing season as well as, for the copepod, temperature and depth. Increases in the density and sound speed contrasts of these species from fall to spring were observed. Target strength predictions based on these measurements varied between fall and spring by 2‐3 dB in krill. Measurements were also conducted on C. finmarchicus lipid extract at changing temperature and pressure. The density contrast of the extract varied negatively with temperature, while the sound speed contrast changed by more than 10 % over the temperature and pressure ranges that the organism expected to occupy. C. finmarchicus target strength predictions showed that the combined effect of temperature and pressure can be significant (more than 10 dB) due to the varying response of lipids. The large vertical migration ranges and lipid accumulation characteristics of these species (e.g., the diapause behaviour of Calanus copepods) suggest that it is necessary for seasonal and environmental variability in material properties to be taken into account to achieve reliable measurements.

감성돔의 음향임피던스 측정

This study was aimed at measuring the acoustic impedance of Japanese black porgy to estimate its sustainable production and resources. The acoustic impedance need to know density contrast and sound speed contrast of target fish. The density contrast is obtained by the Pipette method and sound speed contrast is obtained by the Time-of-flight method. To get basic information on the Japanese black porgy in the experiment, 10 different sizes used. As a result, the body length increases as the weight of the Japanese black porgy was increased. The correlation between the body length and density contrast of the Japanese black porgy was very low. Also, the acoustic speed contrast was shown at very low correlation. However, due to lack of 20~25cm of Japanese black porgy, the standard deviation value is not constant. The impedance results of Japanese black porgy will should be used as basic date of acoustic scattering characteristic and identification of fish.

Ultrasound tomography of materials with high sound speed contrast

Non-destructive evaluation of materials using ultrasounds is frequently used in industry as a way to characterize material properties and to locate defects. Imaging methods based on back propagation of echo signals are limited to reconstruction of low spatial frequency. Ultrasound diffraction tomography is a transmission-based imaging method which gives the possibility of characterizing anisotropic materials. Recent progress in ultrasound tomography using a circular array of transducers enabled velocity mapping of materials with high sound speed contrast relative to the background. In this study, an image of acoustic properties of a titanium rod submerged in water was obtained using bent ray time-of-flight tomography. The experiments were performed on a circular array ultrasonic test bench at 2 MHz frequency on 322 transduction points. A 2D finite element model of wave propagation through water and titanium was developed in order to validate experimental results. Finite element reconstruction matched experimental results within a 10% error for geometry and velocity.

Ultrasonic tomography for multiphase flow characterization

Characterizing multiphase flow dynamics and estimating phase composition are important in many applications including oil/gas production. Conceptually ultrasonic travel-time tomography is an appealing method. It estimates flow phase composition by mapping out the sound speed distribution over a cross section or volume traversed by a large number of travel paths. However, low sound speed contrast over multiphase mixtures imposes high accuracy requirement in travel time estimation which can be especially challenging in the presence of dispersion and multipath interference. On the other hand, high impedance contrast between phases, such as at gas/liquid interfaces, introduces significant losses and hence leads to reduced signal versus noise ratio. In this talk we first provide a characterization of the signal structure based on both numerical wave propagation modeling and lab test data, then we analyze the sensitivity and accuracy requirement for travel time estimation using several different approaches, and finally we evaluate the performance of flow imaging and phase estimation for several common compositional scenarios.

Multiple scattering in resonant emulsions: Coherent-ballistic propagation and diffusive transport

Ultrasonic pulse propagation experiments are reported on dilute suspensions of fluorinated-oil droplets immersed in a water-based gel matrix. These resonant emulsions are model systems for studying the effects of scattering resonances on wave transport since the large sound-speed contrast between the scatterers and the surrounding medium enhances the Mie resonances of the liquid particles. Measurements of the coherent-ballistic component reveal that both the scattering mean free path and the group velocity strongly depend on the frequency as predicted by the Independent Scattering Approximation. Scattering resonances are also responsible for very slow diffusivity of the multiply scattered ultrasound. This slowing down of the diffusion process due to resonances is well captured by models that include additional scattering delays of the ultrasonic pulses. The relationship between the diffusion coefficient and the ballistic data allow the frequency dependence of energy velocity of diffusing waves to be estimated, and show that the energy and group velocities are very different in our system. Although our ultrasonic measurements and their interpretation give a complete picture of wave transport in dilute resonant emulsions, the description of the wave transport in concentrated emulsions requires more sophisticated models based on the spectral function approach and the self-consistent theory.

청어의 음향임피던스 측정

In this study, we confirmed that the weight of herring would increase as its length increases and the relationship between the length and density of the herring would be low. In addition, the sound-speed contrast, which is one of the important factors of the hydro-acoustic impedance, increases as water temperature increases while the sound-speed contrast decreases.BR In order to reduce the error of the TS measurement, it is necessary to apply a proper sonic contrast to the water temperature and behavior patterns of pacific herring. Based on the impedance results of pacific herring, it should be used as the basic data of hydro-acoustic scattering characteristics and identification of the pacific herring.

Measurements of the acoustic properties of crude oil

The acoustic response of crude oil is dependent on the density and sound speed contrast between the oil and the surrounding media. To detect and quantify crude oil in the marine environment, it is crucial to have accurate measures of the density and sound speed at oceanographically relevant temperatures and pressures. A meta-analysis of currently available sound speed data has found a paucity of sound speed data for crude oil at relevant temperatures ( 300K) and pressures (>100 MPa). In order to evaluate the use of currently available data, time-of-flight measurements in a few different types of crude oil were performed in a purpose-built chamber that simulated oceanographic conditions. These test data were compared with extrapolated sound speed curves from currently available data.

Use of SDWBA predictions for acoustic volume backscattering and the Self-Organizing Map to discern frequencies identifying Meganyctiphanes norvegica from mesopelagic fish species

To acoustically assess the biomass of multiple species or taxa within a survey region, the volume backscatter data should be apportioned to the constituent sound scatterers. Typically, measured backscatter is attributed to certain species using predictions at different frequencies, mostly based on the difference in scattering at the frequencies of 38 and 120kHz (dual frequency method). We used the full version of the stochastic distortedwave Born approximation (SDWBA) model to predict backscatter spectra for Meganyctiphanes norvegica and to explore the sensitivities of ΔMVBS to the model parameters, e.g. acoustic frequency and incidence angle, and animal density and sound speed contrast, length, and shape. The orientation is almost the unique parameter responsible for variation, with fatness affecting longer lengths. We present a summary of ΔMVBS that can serve as the basis for identification algorithms. Next, we simulate the scenario encountered in the Balearic Sea (western Mediterranean) where Northern krill are mixed with mesopelagic fish species (bristlemouths and lanternfishes), which are modeled with a prolate spheroid model. Simulated numerical data are employed to emulate the discrimination process with the most common identification techniques and typical survey frequencies. The importance of using density-independent techniques for acoustic classification is highlighted. Finally, an unsupervised neural network, the Self-Organizing Map (SOM), is used to cluster these theoretical data and identify the frequencies that provide, in this case, the most classification potential. The simulation results confirm that pairs of frequencies spanning the Rayleigh and geometric scattering regimes of the targets are the most useful for clustering; a minimum of four frequencies are necessary to separate the three species, while three frequencies are able to differentiate krill from mesopelagic fish species.

Physical Parameter Measurement and Theoretical Target Strength Estimation of Juvenile Cod (Gadus macrocephalus)

The contrast (fish body to medium ratio) of density and sound speed were measured to estimate acoustic scattering from small juvenile cod (Gadus macrocephalus) with the Kirchhoff-Ray Mode backscatter model. The density contrast was measured by the density-bottle method and the sound speed contrast was estimated by the time of flight method. The results revealed that the measured density contrasts of juvenile cod varied between 1.003 and 1.029 (mean = 1.014, S.D. = 0.01). On the other hand, sound speed contrasts varied between 1.039 and 1.041 (mean = 1.041, S.D. = 0.001). The relationship between averaged target strength (TS) and total length (TL) established by the model were <<TEX>$TS_{38kHz}$</TEX>> = 20log(TL) - 68.8 and <<TEX>$TS_{38kHz}$</TEX>> = 20log(TL) - 69.4, respectively.

Measurement of acoustic material properties of macroalgae (Ecklonia radiata)

Temperate macroalgal forests are among the most productive ecosystems in the world. Acoustic propagation measurements have been used to monitor primary production over broad spatial scales (101–103m) in seagrass meadows, and work is in development to assess the application of acoustics for measuring aggregate production in kelp beds and forests. In addition, scientific echosounders have been used routinely for mapping these benthic habitats and, in some cases, identify dominant species. Further advances in these areas require the development of species-specific acoustic models. However there is little knowledge of the acoustic properties of macroalgae, in part because measuring sound speed in large macroalgae is challenging due to their complex morphology. In this study four different methods are developed and trialled to determine the intrinsic sound speed of Ecklonia radiata tissue based on measurement of the time of flight of an ultrasonic pulse, while compressibility is calculated from density measurements. Direct methods involved lengths of stipe and tightly packed stacks of macroalgae blade tissue. Indirect methods focused on an entire intact macroalga submerged in seawater, and a homogenate solution containing seawater and blended blade tissue. Blade tissue showed a density contrast (relative to seawater) of 1.23 and a sound speed contrast of 1.0374 for the stacks. The homogenate solution gave a sound speed contrast of 1.0424. Stipe tissue density and sound speed were lower. Density contrast was 1.04 and sound speed contrasts were 1.0179 (SD=0.0025) and 1.0064 (SD=0.0032) depending on the sample. Whole macroalgae had age- and size-dependent densities with an average density contrast of 1.11 (SD=0.09) and showed an average sound speed of 1572.8m/s (17.8°C) and contrast of 1.0404 (SD=0.0139). Compressibility was higher in stipe than blade tissue, with 3.924e-10Pa−1 and 3.982e-10Pa−1 for stipes and 3.209e-10Pa−1 and 3.180e-10Pa−1 for blade in stacks and homogenate respectively. The results show that E. radiata sound speed and density are higher, and compressibility lower, than that of seawater. This is likely related to high concentrations of alginate, and other structural and storage carbohydrates in the macroalgae, and thus may vary seasonally. The differences between tissue types found for all properties reflect the morphology and anatomy of this macroalga, with tightly condensed chloroplast cells in blade tissue and loosely packed structural cells in the stipe. This research provides essential input parameters to numerical models that will enhance acoustic habitat mapping and allow the development of acoustic inverse methods. This may enable the estimation of aggregate primary production over large spatial scales in temperate kelp habitats, thus informing their future management.

Material properties of Northeast Pacific zooplankton

Abstract We measured the density and sound speed contrasts relative to seawater of Northeast Pacific zooplankton. The density contrast (g) was measured for euphausiids, decapods (Sergestes similis), amphipods (Primno macropa, Phronima sp., and Hyperiid spp.), siphonophore bracts, chaetognaths, larval fish, crab megalopae, larval squid, and medusae. Morphometric data (length, width, and height) were collected for these taxa. Density contrasts varied within and between zooplankton taxa. The mean and standard deviation (s.d.) for euphausiid density contrast were 1.059 ± 0.009. Relationships between zooplankton density contrast and morphometric measurements, geographic location, and environmental conditions were investigated. Site had a significant effect on euphausiid density contrast. Density contrasts of euphausiids collected in the same geographic area ∼4–10 d apart were significantly higher (p&lt; 0.001). Sound speed contrast (h) was measured for euphausiids and pelagic decapods (S. similis) and it varied between taxa. The mean and s.d. for euphausiid sound speed were 1.019 ± 0.009. Euphausiid mass was calculated from measured density and volume, and a relationship between euphausiid mass and length was produced. We determined that euphausiid volume could be accurately estimated from two-dimensional measurements of animal body shape, and that biomass (or biovolume) could be accurately calculated from digital photographs of animals. Data from this study can improve the accuracy of theoretical acoustic scattering models for these taxa, resulting in more accurate estimates of zooplankton biomass in this region.

Material properties of Pacific hake, Humboldt squid, and two species of myctophids in the California Current

We measured the material properties of Pacific hake (Merluccius productus), Humboldt squid (Dosidicus gigas), and two species of myctophids (Symbolophorus californiensis and Diaphus theta) collected from the California Current. Density contrast (g) was measured for pieces of hake and myctophid flesh, and the following Humboldt squid body parts: mantle, arms, tentacle, braincase, eyes, pen, and beak. Density contrast varied with fish species, as well as among squid body parts. Effects of animal length and environmental conditions on nekton density contrast were investigated. Sound speed contrast (h) was measured for hake and myctophid flesh, Humboldt squid mantle and braincase, and varied within and between nekton taxa. These material property measurements can be used to more accurately parameterize target strength models and increase the accuracy of nekton biomass from acoustic surveys.

Material properties of Pacific hake, Humboldt squid, and two species of myctophids in the California Current.

Material properties of the flesh from three fish species (Merluccius productus, Symbolophorus californiensis, and Diaphus theta), and several body parts of the Humboldt squid (Dosidicus gigas) collected from the California Current ecosystem were measured. The density contrast relative to seawater varied within and among taxa for fish flesh (0.9919-1.036), squid soft body parts (mantle, arms, tentacle, braincase, eyes; 1.009-1.057), and squid hard body parts (beak and pen; 1.085-1.459). Effects of animal length and environmental conditions on nekton density contrast were investigated. The sound speed contrast relative to seawater varied within and among taxa for fish flesh (0.986-1.027) and Humboldt squid mantle and braincase (0.937-1.028). Material properties in this study are similar to values from previous studies on species with similar life histories. In general, the sound speed and density of soft body parts of fish and squid were 1%-3% and 1%-6%, respectively, greater than the surrounding seawater. Hard parts of the squid were significantly more dense (6%-46%) than seawater. The material properties reported here can be used to improve target strength estimates from acoustic scattering models, which could increase the accuracy of biomass estimates from acoustic surveys for these nekton.

The Sound-speed and density contrast of Nemopilema nomurai’s umbrella and oral arm

The global warming increased the temperature on the sea surface and consequently, jellyfish numbers rapidly have been increasing. Especially toxic Nemopilema nomurai increased in our coast and gave a lot of damage. To reduce damage, we have to know of distribution the biomass of the jellyfish.<BR> In recent years, to identify biomass distribution of the jellyfish, acoustic technology has been extensively used. This acoustic assessment is required for precise estimate of target strength (TS) of a jellyfish. Among methods to estimate TS, theoretical scattering model method is generally dependent on the sound speed contrast (h) and density contrast (g) of jellyfish.<BR> So, we measured sound-speed contrast and density contrast of the large jellyfish Nemopilema nomurai. This experiment was carried out by separating umbrella and oralarm. The sound-speed contrast was measured by using the time-of-flight method and the density contrast was measured by using volume-mass method. The measured sound-speed contrast varied between 0.9977 and 1.0027 (mean 1.0005) in umbrella and between 0.9957 and 1.0014 (mean 0.9985) in oralarm. The measured density contrast varied between 0.9878 and 0.9981 (mean 0.9930) in umbrella and between 1.0029 and 1.0060 (mean 1.0044) in oralarm. There was a difference in sound speed contrast and density contrast of umbrella and oralarm of Nemopilema nomurai.

Design of a fluorinated magneto-responsive material with tuneable ultrasound scattering properties

In this work, we describe the preparation of emulsions of fluorinated ferrofluid droplets suspended in a yield-stress hydrogel (Bingham fluid) with potential applications for ultrasound (US) spectroscopy and imaging. Fluorinated ferrofluids were obtained using an original multi-step process leading to an appropriate suspension of magnetic nanoparticles (MNPs) coated by a layer of fluoroalkylsilane in fluorinated oil. The efficiency of the sol-gel coating reaction was assessed by several methods including infrared and X-ray photoelectron spectroscopy, small angle neutron scattering and magnetometry. The resulting suspension of silanized-MNPs behaves as a true fluorinated ferrofluid, remaining stable (i.e. a monophasic suspension of well dispersed MNPs) in magnetic inductions as high as 7 T. These ferrofluids were employed to prepare monodisperse emulsions in a Bingham gel using a robotic injection device. Using ultrasound spectroscopy, we show that the emulsion droplets behave as Mie-type acoustic wave resonators due to the high sound-speed contrast between the droplets and the matrix. When subjected to a magnetic field, the ferrofluid droplets elongate in the field direction, which in return modifies the acoustic response of the material. The resonance frequency peaks scale as the inverse of the emulsion droplet size encountered by the wave propagation vector. These results might open a new road towards the realisation of ultrasound contrast agents guided by magnetic fields and with a tuneable attenuation spectrum.