Making Waves with Sound Velocity in Water

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.]

A simple and accurate formula for the sound velocity in water

A method for measuring the change of sound velocity from a reference state in a liquid is described. Two interdigitial transducers on a piezoelectric substrate are in contact with the liquid, and are used as an input and an output transducer for constructing a liquid delay device. The phase difference between an input and a delayed output signal is detected as a dc voltage via a phase comparating circuit. The temperature dependence of the sound velocity in water, measured by the present method, agrees well with the published data. The influence of hydrostatic pressure on the sound velocity in water is given.

The aqueous suspension of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) vesicles with different hydration levels α (water-to-lipid mass ratio) have been studied by Brillouin spectroscopy in the temperature range from −190 °C to 70 °C. The samples with different hydration levels demonstrate similar temperature behavior of their sound velocity in the temperature range from −190 °C to −25 °C. There is a strong correlation between the hydration level of the sample and the character of the sound velocity temperature dependence at higher temperatures. Nevertheless, all hydrated samples demonstrate a jump in the sound velocity at the gel–fluid phase transition temperature. The amplitude of this jump depends on the hydration level α of the sample. It has a maximum value in the sample with minimal α necessary for the phospholipid membrane's full hydration. To evaluate the sound velocity in the phospholipid membrane, we applied the two-component model to analyze the experimental data obtained in the sample with α = 0.25 (close to the minimal necessary value for the full DPPC membrane hydration). It was found that for temperatures higher than 0 °C, the two-component model works well if we consider that sound velocity in water between vesicle layers is approximately a factor of two higher than in bulk water.

INTRODUCTION A new technique for the spectral energy analysis of acoustic data taken during bottom and subbottom profiling surveys will be described. This technique is intended to be an additional tool for the evaluation and analysis of subbottom data. Single frequency acoustic systems [sonars] are widely used for bottom and subbottom profiling in shallow and deep waters. The system consists of a pulsed transmitter, a transducer or transducers for coupling acoustic energy into and out of the water, a receiver and a display such as a graphic recorder. A single transducer may be used as both the transmitter and receiver, or separate units can be employed. Transducers may be mounted to a ship's hull, or in towed vehicles [fish]. The echoes from the bottom and subbottom features are displayed on the recorder for immediate evaluation, and can also be recorded on magnetic tape for further processing. It is the purpose of the new analysis technique to extract additional information from these echo signals to allow more accurate identification of features and properties of the bottom and subbottom. This method, when used in conjunction with bottom sampling and coring operations, can establish the basic reference datums for a computer-aided automatic analysis system. When fully operational, this system with automatically identify subbottom materials and geologic features. The data display of conventional profiling recorders will be reviewed and then the basis of the new technique will be presented. The new display resulting from the energy analysis will be examined using acoustic signals from several sources, and the basic computer aided analysis system will be described. ACOUSTIC PROFILING Basic System Charts Classically, the data gathered from subbottom surveys is presented as a profile chart shown in Fig. 1. These records are interpreted and analyzed relying on prior experience in reading the records) and correlation with core borings is used to identify specific materials. The abscissa [horizontal axis] is the linear distance along the survey track and is a function of the speed of the transducer over the bottom. The ordinate is the time for the echo to return to the receiving transducer and is calibrated in depth [feet or fathoms] of the reflection below the transducer. The depth calibration is based on a sound velocity in water. The depth calibration is corrected for the two-way travel of the sound energy from transducer to bottom to transducer. The intensity of the echo is a function of both the reflecting material and the acoustic properties of adjacent strata. Therefore) in order to completely identify a particular subbottom layer) it is necessary to evaluate the echo from that layer of interest in conjunction with the echoes from overlying material. These echoes are qualitative indications of the acoustic parameters of the strata. The analysis and interpretation of these parameter must start from scratch, due to the lack of any established standards against which new data can be evaluated.

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.

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.

In this paper, an underwater ranging system based on photoacoustic effect occurring on target surface is proposed. In this proposal, laser pulse generated by blue-green laser is directly incident on target surface, where the photoacoustic effect occurs and a sound source is formed. And then the sound wave which is also called photoacoustic signal is received by the ultrasonic receiver after passing through water. According to the time delay between transmitting laser and receiving photoacoustic signal, and sound velocity in water, the distance between the target and the ultrasonic receiver can be calculated. Differing from underwater range finding by only laser, this approach can avoid backscattering of laser beam, so easier to implement. Experimental system according to this principle has been constructed to verify the feasibility of this technology. The experimental results showed that a ranging accuracy of 1 mm can be effectively achieved when the target is close to the ultrasonic receiver.

Some Algorithms of AUV Positioning Based on One Moving Beacon

Studies in waterbodies with peculiar salinity face problems in determining water salinity (mineralization). The conventional methods of determining salinity from conductivity or, in the past, chlorinity can yield significant errors. This article compares two methods for determining water salinity: the solid residue method and the measurement of sound velocity in water. It has been shown that the measurement of sound velocity (and temperature) can be used for reliable in situ determination of water salinity that is almost unfeasible by other methods (applicable only under laboratory conditions or yielding insufficient accuracy). Results of water salinity determination in different regions of the Aral Sea in 2012–2015 are presented.

A technique is described in which the ultrasonic time delay between successive echoes in an echo train is determined by phase comparison of the echoes with a coherent continuous signal. Corrections for phase shift of an echo upon reflection from the face of a transducer and for diffraction effects are discussed. The velocity of sound at 1 MHz in distilled water from 23° to 75°C has been measured with this technique. Measurements of time delay are accurate to 20 ppm while the over-all accuracy is 127 ppm or ±0.20 m/sec. Excellent agreement with values in the literature is found.

The quantitative measurement of acoustic properties is indispensable for many applications. The realization of devices for the evaluation of acoustic properties with higher accuracy and lower error is of great importance. Moreover, the ability to obtain the high-frequency acoustic characteristics of materials is also highly desirable. In this research, the pulse echo method is applied to measure a material’s acoustic parameters, using a miniature transducer with a center frequency of 42.9 MHz. For this method, only one transducer is needed, and the measurement system is simple. Acoustic parameter calculation methods for three types of materials are studied, and the corresponding experiments are conducted. The experimental results show that the sound velocity of water is 1508.8 m s−1, and its attenuation coefficient is 0.981 dB mm−1; the results for liquid paraffin give results of 1386.8 m s−1 and 2.35 dB mm−1, respectively. With reference to polymer materials, thermoplastic polyurethane (TPU) thin film has a sound velocity of 1987.2 m s−1 and an attenuation of 37.1 dB mm−1, and polyimide thin film has a sound velocity of 2142.3 m s−1 and an attenuation of 25 dB mm−1. In terms of ceramics, the sound velocity of PZT-5H 3203HD is 4804.2 m s−1, and its attenuation is 1.71 dB mm−1; 96% alumina ceramic has a sound velocity of 9924.9 m s−1 and its attenuation 1.18 dB mm−1. All results pertaining to sound velocity agree well with those reported in previous works. The measured attenuation coefficients at high frequency are also in good agreement with the experimental data. All experimental results validate the feasibility, effectiveness, convenience, and accuracy of this method.

The velocity of sound in water has been measured by an ultrasonic echo technique in the temperature range from — 12°C to 129°C under hydrostatic pressures varying up to 9600 kg/cm2. Even at the highest pressures the temperature dependence of the velocity of sound is found to be abnormal. In contradiction to certain previous results, the temperature at which the velocity of sound is a maximum is found to increase with increasing pressure. The behavior of the sound velocity is discussed in the light of recent theories concerning the structure of water. The internal consistency of the data with existing pressure standards is also analyzed.

With the development of national marine strategic plan, the demand of underwater high-precision positioning is increasing greatly. Acoustic wave, as an information carrier, plays an important role in underwater high-precision positioning. In this paper, the method of determining sound velocity in seawater and several classical models for calculating sound velocity are introduced. The indirect method is used to calculate the sound velocity of sea water, that is, the sound speed is calculated by the sound velocity empirical model according to the depth, temperature and salinity. Then, several classical sound speed models are used to select the optimal model under different computational conditions, and the most suitable model for the study sea area is obtained. Calculation of sound velocity profile based on the real time observation data of Argo measured by the official website combined with the optimal classical sound velocity model. The sound velocity is corrected by the weighted average sound velocity method and the layered ray tracing method, and the depth of the sea is recovered. Results show that the accuracy of tracking method is higher than that of the weighted average sound velocity method, which can achieve decimeter level precision in depth. The error between the calculated depth and the actual value by using the weighted average sound velocity method is large.

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.