A New Technique for Acoustic Data Analysis

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 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.

A simple and accurate formula for the sound velocity in water

Two types of the subsurface layers were investigated by two Boreholes on the two banks of the Shatt Al Arab River near the old Al-Rebat port at Basrah city. Sub Bottom Profiling along the River section has also been investigated. The boring was carried out in two sides of Shatt Al-Arab at Al-Ashar and Al-Tanuma sides at Al-Rebat square. Marine geophysical investigations were made including Sub Bottom profile technique (SBP) using the Strata Box instrument. Besides, Acoustic Doppler Current Profiler (ADCP) technique was used along a 400 m section for determining the cross section of the River. the Boring Log Data of two Boreholes have been represented depending on SPT Values as the bearing Strength of subsoil layers profiles, which is matching with the sedimentary layers resulting from the seismic profiles for obtaining the geotechnical model of subsurface layers along cross section of the River. High bearing capacity layer is very dense sandy layer which appears at -22m of the elevation on sea level and extends to -29 m in left bank of the River. This layer is old deposits belonging to Dibdiba deposits (upper Miocene-Pleistocene).
 

A case study on pseudo 3-D Chirp sub-bottom profiler (SBP) survey for the detection of a fault trace in shallow sedimentary layers at gas hydrate site in the Ulleung Basin, East Sea

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.

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.

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.

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.

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

Making Waves with Sound Velocity in Water

In the context of deep-water ocean exploration, sub-bottom profiling and multibeam bathymetric surveys are frequently integrated and synchronised to facilitate the concurrent acquisition of deep-water seafloor topography and fine sedimentary stratigraphic data. However, the complex topographic changes present in the deep ocean pose significant challenges in the exploration of the accuracy of deep-sea sub-bottom profiles. These challenges include the real-time tracking of the seafloor reflector and the splicing of profiles derived from deep-sea long-term reflection data. The accurate determination of the seafloor reflecting depth is a prerequisite for the effective correction of the data volume of deep-sea sub-bottom profiles. The development of a precise positioning and noise suppression method, namely the nearest position pair and the inverse distance weighted interpolation algorithm, has enabled the correction of the seafloor’s reflecting depth and the effective splicing of sub-bottom profile data in deep water. The enhancement of the quality of deep-water sub-bottom profile data is facilitated by these processing techniques, thereby enabling the provision of a comprehensive and successively long profile for interpretation in the context of deep-water sub-bottom profile data.

Remote acoustic characterization of the physical properties of marine sediments is of great interest to the geological and acoustical communities to display different subbottom layers and to collect information about acoustic sound propagation at low frequencies. Subbottom profilers are designed to generate cross-sectional images of ocean sediment layering. Energy reflected from the subbottom layers responding to artificial acoustic source excitation is recorded as a time series called a trace. A subbottom profile image is composed of adjacent traces. The aim of the interpretation of these images is to identify the sediment layers and later to build a sedimentary database. The automatic mapping of subbottom layers should significantly speed up data analysis. We develop, keeping this aim in mind, an image processing algorithm for automatically outlining the sediment layers in subbottom profiler images. This algorithm is based on the wavelet packet analysis and a correlation criterion.