Sound Velocity In Water Research Articles

Water velocity estimation using inversion methods

It is known that the propagation velocity of sound waves in water can vary over time. For a 3D seismic survey, if data are acquired in adjacent lines but at different dates, this implies the same reflection point will be recorded at different times. To take this effect into account in seismic processing, it is necessary to measure the sound velocity in water. I have developed a 3D tomographic method that directly estimates it. It assumes a constant sound velocity for a group of shots belonging to a single sail line. Using a picked water-bottom reflection and an initial depth and velocity model, results good for use in subsequent processing can be obtained by estimating only two parameters: the variation of the propagation velocity and a constant vertical shift of the reflector depth in relation to the initial model. The method was tested with both synthetic and real data. The real data results were validated using two methods. First, I analyzed the histogram of the residuals of the final updated model. Second, I used a specially modified Kirchhoff migration algorithm to migrate the sea bottom. The main advantages of this method are that it takes into account the sea-bottom dips to estimate the velocities and it can be applied to each sail line separately. Also, the inversion is not ill-conditioned provided that data with large enough offsets are used. As a result, the method is simple to apply.

Measurement of Sound Velocity in Water Using Optical Probe and Acoustical Holography

We propose a method for a determination of a three‐dimensional sound velocity using optical computerized tomography (O‐CT) and near‐field acoustical holography (NAH) for measuring a phase object. Ultrasonic waves affect a phase of the light passing through radiated sound fields. The zeroth order diffraction light including sound pressure information is acquired by an avalanche photodiode. Eighteen projections are acquired by rotational scanning, and each projection along the optical axis is obtained by single linear scanning and electronically quadrature‐detected as the complex amplitude. The complex sound fields are reconstructed by O‐CT in a region of 40 × 40 mm2. Then the sound field on another plane is propagated using NAH from the acquired sound fields, and the sound field on the same plane is reconstructed by O‐CT. Comparing the phase of propagated and reconstructed sound fields in wavenumber domain, we can obtain the sound velocity in three dimensional space in a region of 30 × 30 × 10 mm3. The experimental results are in agreement with the reference value measured by another mean.

Temperature-dependent diffusing acoustic wave spectroscopy with resonant scatterers

The influence of a slight temperature change on the correlation of multiply scattered acoustic waves is studied, and experimental results are discussed. The technique presented here, similar to diffuse acoustic wave spectroscopy, is based on the sensitivity of a multiple scattering medium to a slight change. Ultrasonic waves around 3 MHz are transmitted through a sample made of steel rods in water and recorded by an array of transducers at different temperatures. The cross-correlations between highly-scattered signals are computed. The main effect of the temperature change is a simple dilation of the times of arrival, due to a change of the sound velocity in water. But the scatterers also play a role in the progressive decorrelation of waveforms. An analysis resolved in both time and frequency shows that at some particular frequencies, the resonant behavior of the scatterers are responsible for a significantly larger decorrelation. Interestingly, the experimental results allow one to detect the presence of a small resonance that was not detected earlier on the same scatterers with classical measurement of the scattering mean freepath. A simple model is proposed to interpret the experimental results.

Temperature-dependent diffusing acoustic wave spectroscopy with resonant scatterers

The influence of a slight temperature change on the correlation of multiply scattered acoustic waves is studied, and experimental results are discussed. The technique presented here, similar to diffusing-acoustic-wave spectroscopy, is based on the sensitivity of a multiply scattering medium to a slight change. Ultrasonic waves around 3 MHz are transmitted through a sample made of steel rods in water and recorded by an array of transducers at different temperatures. The cross correlations between highly scattered signals are computed. The main effect of the temperature change is a simple dilation of the times of arrival, due to a change of the sound velocity in water. But the scatterers also play a role in the progressive decorrelation of wave forms. An analysis resolved in both time and frequency shows that at some particular frequencies, the resonant behavior of the scatterers is responsible for a significantly larger decorrelation. Interestingly, the experimental results allow one to detect the presence of a small resonance that was not detected earlier on the same scatterers with classical measurement of the scattering mean free path. A simple model is proposed to interpret the experimental results.

Parameters of microparticles responsible for the monopole sound scattering in a liquid

A monopole scattering of sound by microparticles in a liquid is considered for microparticles of two types: spherically symmetric particles similar to gas bubbles in a liquid and disk-shaped gas-filled particles whose bases may oscillate in antiphase. A transformation of the scattering amplitude to the function that, in particular, describes the oscillations of a particle removed from the liquid is proposed. This function extends the possibilities of the acoustic diagnostics of such particles. Estimates of the sound velocity in water containing disk-shaped particles suggest that the sound velocity increase observed in sea water with plankton can be explained by the monopole scattering of sound from a single plankton particle modeled as a rigid gas-filled disk with oscillating parts of its bases.

Inverse boundary value problem for ocean acoustics

For an ocean with constant depth and rigid bottom which contains compactly supported inhomogeneity of the water sound velocity, we prove uniqueness for the identification of the inhomogeneity from the Dirichlet-to-Neumann (DtN) map on the surface of a bounded region containing the inhomogeneity. The DtN map is the map which maps the pressure applied on the boundary of this region to the corresponding flux (displacement). In an analogous geometric configuration and with similar boundary conditions, the uniqueness for the inverse electroconductivity problem from the DtN map (i.e. voltage-to-current map) can be proved in the same framework. Copyright © 2001 John Wiley & Sons, Ltd.

A comparative study on the modeling of sound pressure field distributions in a sonoreactor with experimental investigation

In sonochemical reactors the effect of emerging cavitation bubbles has significant influence on the amplitude and structure of the developing sound field. Calculations show that the damping parameter and the phase velocity may, depending on the pressure amplitude, change by several orders of magnitude. For example, the sound velocity in water comes to 1500 ms −1, whereas in a bubbly liquid it may decrease to 20 ms −1, which is much below the velocity of sound in air (about 340 ms −1). In this paper, a method of calculating the time dependent three-dimensional pressure field in sonochemical reactors of various shapes is presented. It takes into account inhomogeneous distributed wave parameters which are a function of the spatial depending pressure amplitude. The modeled results are then compared with experimentally measured values of a certain kind of reaction vessel. The agreement is found to be satisfactory.

Experimental analysis of acoustic scattering from lengthwise soldered cylindrical shells

Through an experimental approach, this paper explores the acoustic wave scattering processes involved in the acoustic backscattering from air-filled submerged cylindrical shells having axial discontinuity. The discontinuity is caused by lengthwise soldering along the tubes in the course of manufacture from flat sheets, and is represented as an internal axial mass layer. The tubes are excited by a plane wave at normal incidence. In the time domain, different echoes on short pulse responses (echo wave forms), are identified by the arrival times and related wave type. This enables the localization of additional wave generating sites and scattering centers due to the solder. A number of detected echo series are thus identified. In the frequency domain analysis, the influence of supplementary echoes and that of inter-echo interferences on both backscattering and resonance spectra is presented. The influence of the angular position of the solder, relative to the direction of the incident sound wave, on the amplitudes of spectra, is analyzed. The key phenomena in this study are wave generation at the solder when it is directly insonified (prevalent over classical wave generations of considered waves) and the wave type conversions observed when propagating waves encounter obstacles in the shell, geometric or material discontinuities (in this case the solder). The wave types studied are the A wave (Scholte–Stoneley) and the S0 compressional wave, in the midfrequency region, ka=25–90, where k=ω/C1 is the wave number in water, C1 is the sound velocity in water and a the external radius of the tube. This analysis of the influence of discontinuities in the propagation medium on the acoustic scattering is carried out with a view to the investigation of scattering of assembled objects such as cylindrical shells with hemispherical endcaps.

A simple and accurate formula for the sound velocity in water

The sound velocity in test objects and phantoms is often measured by performing a differential measurement with pure water. To promote standardization, a simple formula for the sound velocity in water is derived that renders true values within 0.20 m s −1 over the temperature range 15–35 C. The formula is given by c = 1404.3 + 4.7 T − 0.04 T 2, with sound velocity c in m s −1 and temperature T in C.

Improved processing of Hydrosweep DS multibeam data on the R/V Maurice Ewing

We have developed a new software package, called MB-System, for processing and display of Hydrosweep DS multibeam data on the R/V Maurice Ewing. The new software includes tools for modeling water sound velocity profiles, calculating multibeam bathymetry from travel time values by raytracing through a water sound velocity profile, interactive and automatic editing of multibeam bathymetry, as well as a variety of tools for the manipulation and display of multibeam data. A modular input/output library allows MB-System programs to access and manipulate data in any of a number of supported swath-mapping sonar data formats, including data collected on Hydrosweep DS, Sea-Beam “Classic”, SeaBeam 2000, SeaBeam 2100, H-MR1, Simrad EM12, and other sonars. Examples are presented of the software's application to Hydrosweep data recently collected on the R/V Maurice Ewing.

Test of the equation of state of water up to freezing at 100 and 200 °C

The sound velocity in water at 100 and 200 °C has been determined up to the freezing pressure using Brillouin scattering. In this temperature and pressure range there is little experimental data on any physical property of water. Our results, therefore, provide a convenient test of existing equations of state. We find our results to be in good agreement with those calculated from the most reliable equation of state.

Making Waves with Sound Velocity in Water

Making Waves with Sound Velocity in Water

Equivalence of the sound velocity in water and ice at mesoscopic wavelengths

IT is generally assumed, for any material, that sound travels faster in the solid phase than in the liquid. This is true at least for waves of macroscopic wavelength, the dynamics of which depend on the elastic properties of the medium and, hence, on the presence or absence of long-range order. But at wavelengths approaching the typical interparticle distance, the dynamics should become insensitive to the long-range organization of the medium. Here we report inelastic X-ray scattering measurements in water and ice, which show that sound waves with wavelengths between 0.5 and 3nm propagate at the same velocity in both phases. The observed sound speed, which is greater than twice the hydrodynamic speed of sound in water, but less than that in ice, agrees with values obtained in previous measurements of 'fast sound' in liquid D2O (ref. 1) and H2O (ref. 2). These results show that, despite the fundamental structural and dynamical differences between water and ice, the dynamical response of the two phases is strikingly similar at very short wavelengths.

Aircraft laser sensing of sound velocity in water: Brillouin scattering

A new real-time data source for sound speed in the upper 100 m has recently been proposed for exploratory development at the Naval Oceanographic and Atmospheric Research Laboratory. This data source would be generated via a ship- or aircraft-mounted, optical pulsed laser using the technique of spontaneous Brillouin scattering. This system should be capable (from a single 10 ns 500 mJ pulse) of yielding range resolved (≈ 1 m resolution) sound speed profiles in water to depths of 75–100 m to an accuracy of 1 m/s. At aircraft speeds of 300 miles/h (134 m/s) and a laser pulse repetition rate of 10 pps, vertical profiles of sound speed would be obtained spatially every 13 m. These 100 m profiles would provide the capability of rapidly monitoring the upper-ocean vertical structure for much of the world's oceans and for most seasons. They would provide new perspectives on upper-ocean mixing and the oceanic internal wave field. These profiles would also provide an extensive, new, subsurface-data source to existing real-time, operational ocean nowcast/forecast systems. The present systems are dependent on sparse bathythermograph data and information inferred from sea-surface data. Extension of the 100 m profiles to depth using existing and proposed techniques would further increase the value of the laser-derived information.

On the dispersion of Scholte wave propagating on a layered medium

The phase velocity of the Scholte wave is experimentally studied in the case of plane multilayered systems immersed in water. The ‘‘liquid wedge’’ technique is used for its generation and the investigation is limited to the case where the layers have a high density and a high shear wave velocity with respect to the fluid (water). The variations of the difference between the phase velocity of the Scholte wave and the sound velocity in water is obtained by recording the ‘‘penetration factor’’ of the investigated wave into the liquid, the amplitude of which decays exponentially as exp(−k″z) from the surface; z measures the coordinate perpendicular to the interface and k″ designates the ‘‘penetration factor.’’ The agreement between theoretical and experimental results is reasonably good. The method of investigation limits our study on the dispersion of the Scholte wave to the ke values>1.8 (k designates the wave vector in the water and e the thickness of the layer).

Aircraft laser sensing of sound velocity in water: Brillouin scattering

This study shows that it may be feasible using state-of-the-art pulsed lasers, coupled with a novel technique for maintaining laser line stability, to design, construct, and operate an airborne laser system to remotely measure sound velocity in water. This system should be capable of yielding range-resolved (3-m bins) sound velocity in water to depths of 75 m to an accuracy of 1 m/s. Flying at aircraft speeds of 300 mi/h and operating at a laser repetition pulse rate of 10 pps, vertical sound profiles would be obtained every 44 ft. Such upper-ocean high-vertical-resolution profiles of sound speed would be useful to various Naval applications. They could serve as stand-alone data sets or combined with other real time and/or historical data sets to yield improved acoustic and oceanographic prediction models. [Work supported by NOARL.]

Transient Processes at the SI-Water Interface During Pulsed Laser Irradiation

ABSTRACTHeat transfer processes and phase transitions at the Si-water interface during nanosecond pulsed laser irradiation were studied in real time using transient optical reflectance measurements. Measurements at two probe laser polarizations suggest that during irradiation a steam phase is formed near the Si surface. Relaxation of this phase occurs several hundred nanoseconds after solidification of the Si is completed. Acousto-optical measurements indicate that a shock wave, propagating with the sound velocity in water, is initiated near the Si-water interface.

Normal mode measurements and remote sensing of sea-bottom sound velocity and attenuation in shallow water

The dispersion analysis of explosive signals and measurements of individual mode attenuation in the Yellow Sea is reported. By adjusting input parameters of a normal mode computer program and making the calculated results coincide with field data, the compressional wave velocity and attenuation in the sediment for the frequency range of 80–800 Hz is simultaneously deduced. The sea-bottom velocity, attenuation, and its frequency dependence, probed from two sea areas with a different depth and sound velocity profile in the summer and the winter, are very close. Resultant sea-bottom attenuation approaches the results of earlier workers at the upper end of the frequency band and joins with the data obtained by others at the lower end, and the absorption appears to have a nonlinear frequency dependence (α=0.37 f1.84 dB/m kHz). The errors due to the change of environmental parameters (such as water depth, water sound velocity profile, sediment density, and seafloor roughness) are discussed.

The empirical age‐depth relation and depth anomalies in the Pacific Ocean Basin

This paper presents a new age‐depth relation and a comprehensive depth anomaly map for the Pacific Ocean. Age, depth, and sediment thickness were averaged for each 1°×1° area. Bathymetry was corrected for isostatic effects due to sediment and water load and for the variation of sound velocity in water. Seafloor existing at extreme distance from hot spot tracks is found to be anomalously deep. Hot spots were treated as thermal anomalies, and data within 800 km of them were eliminated from further analysis. An age‐depth equation was determined by fitting a least squares line to the remaining data. The resulting depth versus age distribution confirms the linear dependence of depth on √age up to 80 Ma. All older seafloor is within 800 km of hot spots or hot spot tracks and is shallower than predicted. This “flattening” of the age‐depth distribution requires that a separate function be fit to data older than 80 Ma. As a result, data representing the deepest seafloor (older than 80 Ma) were selected for curve fitting, and the age‐depth distribution was approximated by an exponential function. It is impossible to distinguish between the infinite half space and cooling plate models of the lithopshere using the age‐depth data from the Pacific Ocean. A depth anomaly map prepared by comparing observed depth with the depth predicted by the new age‐depth formula shows several newly recognized features, including swells over the Louisville Ridge in the South Pacific and in the Gulf of Alaska Seamounts.

Sediment contributions to group velocity in shallow water

Dispersion curves are used to examine the effect of sediments on group velocity, and the problem further dissected by a direct look at the relative contributions of the sediment layers to the group velocity integral. The environments of interest have water depths less that 150 m and sediment thickness of the order of 50 m. The range of frequencies considered is between 25 and 600 Hz. A systematic variation of sediment types and velocity profiles will be examined to find features of the dispersion curves which might be used to extract information about the bottom from shot data. In the presence of stable water velocity profiles, gradients in the sound velocity in the sediment can be detected, as can layering, provided such layers are near the water-sediment interface. Highly variable water sound velocity profiles limit information available concerning the sediment to gross features such as sediment type. [Work supported by Naval Ocean Research and Development Activity.]