Acoustic Tomography Technique Research Articles

Improving the accuracy of streamflow data acquired from the acoustic tomography technique using data despiking algorithms

Streamflow is an important hydrological factor in water resources management. The Fluvial Acoustic Tomography (FAT) as a cutting-edge river monitoring technology measures the flow velocity using the travel time of the acoustic signals. The velocity is then multiplied by the river cross-section to obtain accurate and continuous streamflow data. Similar to all acoustic instruments, the FAT output velocity contaminated by spike data. Standard deviation (STD) as a simple method of spike removing, was used in previous FAT studies. The disadvantages of the STD method are that it not only does not replace the identified spikes with the appropriate values and therefore results in measurement discontinuity, but it also requires engineering judgment that may increase the measurement error. In this study, two despiking methods, i.e., Phase-Space Thresholding (PST) and three-dimensional Rousseeuw Phase-Space thresholding (3D-RPS) are applied to detect/modify outliers of a 6-day FAT velocity signals. The results showed that the 3D-RPS method has the best performance with a Nash-Sutcliffe efficiency coefficient (NSC) of 0.731 compared to 0.572 and 0.44 NSC values of STD and PST methods, respectively. The FAT-based streamflow data were also compared with the reference streamflow obtained from the Rating-Curve method. The results reveal that the streamflow measurement accuracy improves significantly, where the relative errors decrease from ± 40% for the STD method to ± 15% for the 3D-RPS approach. As a result, the 3D-RPS approach appears to be an effective method for improving the accuracy of the FAT-acquired streamflow data.

Layer-Averaged Water Temperature Sensing in a Lake by Acoustic Tomography with a Focus on the Inversion Stratification Mechanism.

Continuous sensing of water parameters is of great importance to fluid dynamic progress study in oceans, coastal areas and inland waters. The acoustic tomography technique can perform water temperature field measurements horizontally and vertically using sound wave travel information. The layer-averaged water temperature can also be measured with the acoustic tomography method. However, investigations focusing on the stratified mechanism, which consists of stratification form and its influence on inversion error, are seldom performed. In this study, an acoustic tomography experiment was carried out in a reservoir along two vertical slices to observe the layer-averaged water temperature. Specifically, multi-path sound travel information is identified through ray tracing using high-precision topography data obtained via a ship-mounted ADCP during the experiment. Vertical slices between sound stations are divided into different layers to study layer division inversion methods in different preset types. The inversion method is used to calculate the average water temperature and inversion temperature error of every layer. Different layer methods are studied with a comparison of results. The layer division principle studied in this paper can be used for layer-averaged water temperature sensing with multi-path sound transmission information.

Influence of Suspended Sediment Concentration and Particle Sizes on the Sound Attenuation of the Fluvial Acoustic Tomography Technique

Fluvial Acoustic Tomography System (FATS) as an advanced technology acquires continuous streamflow data in rivers and estuaries even during floods. However, the acoustic signals are dramatically attenuated by suspending sediments which this problem is a new field of study. In this study, we propose a new equation to estimate the maximum applicable measurement distances (MAMDs). It is based on the cross-sectional suspended sediment concentration (<SSC>) and the particle sizes on the 30-kHz FATS. Our study results show that MAMD might be 2,380 m in the clear water. Moreover, the streamflow monitoring can be perfectly done while <SSC> is less than 12.67 kg/m3 with the particle radii of 3 μm, when the horizontal distance between two acoustic stations is 100 m. Also, the acoustic signals are not decayed if the particle radii equal to 20 mm and the maximum <SSC> is 6.6 kg/m3. This study highlights the performance of FATS in the presence of high <SSC> and provides a better perspective of applying FATS in different rivers with high variability of <SSC>.

Continuous Monitoring of Tidal Bores Using Acoustic Tomography Technique

Continuous Monitoring of Tidal Bores Using Acoustic Tomography Technique

An Acoustic Tomography Technique for Concurrently Observing the Structure of the Atmosphere and Water Bodies

AbstractThe opacity of water to radio waves means there are few, if any, techniques for remotely sensing it and the atmosphere concurrently. However, both these media are transparent to low-frequency sound (&lt;300 Hz), which makes it possible to contemplate systems that take advantage of the natural integration along acoustic paths of signals propagating through both media. This paper proposes—and examines with theoretical analysis—a method that exploits the harmonics generated by the natural signature of a propeller-driven aircraft as it overflies an array of surface and underwater sensors. Correspondence of the projected and observed narrowband acoustic signals, which are monitored synchronously on board the aircraft and by both sensor sets, allows the exact travel time of detected rays to be related to a linear model of the constituent terms of sound speed. These observations may then be inverted using tomography to determine the inhomogeneous structures of both regions. As the signature of the aircraft comprises a series of harmonics between 50 Hz and 1 kHz, the horizontal detection limits of such a system may be up to a few hundred meters, depending on the depth of the sensors, roughness of the water surface, errors due to refraction, and magnitude of the sound field generated by the source aircraft. The approach would permit temperature, wind, and current velocity profiles to be observed both above and below the water’s surface.

Electrical and Reliability Performance of Molded Leadless Package for High-voltage Application

This paper investigates the influence on electrical and reliability performance of molded leadless package for high-voltage power integrated circuit application. Semiconductor devices are mostly encapsulated by using epoxy molding compounds which act as protection for the ICs from damage to the harsh environment. Quad Flat No Lead was selected since the application requirement for compact AC to DC portable adapter charger and more input and output pin. High-voltage package was designed based on the IPC-2221 standard specification and creepage distance was calculated under external component lead, uncoated. Two epoxy molding compounds were used namely as type A and B. Key properties of EMCs were identified such as ionic content, glass transition temperature and volume resistivity. The electrical tested at room temperature on high-voltage leakage current at 700V showed EMC B has no failure compared with EMC A. On top of that, electrical parametric distribution showed that the Cpk of EMC B was extremely robust compared with EMC A. Reliability test was conducted for high temperature operating life test at 115˚C and EMC B was passed up to 1000hours while EMC A was failed. Meanwhile, High Temperature Storage Life test at 150˚C and Temperature Humidity Bias Test at condition 85˚C, 85% relative humidity showed that EMC B was passed for 1000hours but EMC A was failed at 168hours. However, both compounds A and B were passed delamination criteria tested by scanning acoustic tomography technique before and after subjected to moisture sensitivity level 1.

Materials Stress Diagnostics by X-Ray and Acoustic Techniques

Abstract Performed investigations and obtained results concerned the analysis of residual stresses in near-surface areas of coppercorundum (Cu-Al2O3) composite and silicon carbide (SiC) samples. X-ray diffraction and acoustic tomography techniques, as well as the suitable calculation procedures, allowed to locate sample-areas with extreme values of stresses residing in the examined materials. The registered texture-stress characteristics reflects inhomogeneity of the samples structure identified by means of acoustic tomography. Obtained results provide valuable information on anisotropy of physical properties of structural elements produced by the technologies applied to the examined samples.

Difference-frequency generation in nonlinear scattering of acoustic waves by a rigid sphere

In this paper, the partial-wave expansion method is applied to describe the difference-frequency pressure generated in a nonlinear scattering of two acoustic waves with an arbitrary wavefront by means of a rigid sphere. Particularly, the difference-frequency generation is analyzed in the nonlinear scattering with a spherical scatterer involving two intersecting plane waves in the following configurations: collinear, crossing at right angles, and counter-propagating. For the sake of simplicity, the plane waves are assumed to be spatially located in a spherical region which diameter is smaller than the difference-frequency wavelength. Such arrangements can be experimentally accomplished in vibro-acoustography and nonlinear acoustic tomography techniques. It turns out to be that when the sphere radius is of the order of the primary wavelengths, and the downshift ratio (i.e. the ratio between the fundamental frequency and the difference-frequency) is larger than five, difference-frequency generation is mostly due to a nonlinear interaction between the primary scattered waves. The exception to this is the collinear scattering for which the nonlinear interaction of the primary incident waves is also relevant. In addition, the difference-frequency scattered pressure in all scattering configurations decays as r-1lnr and 1/r, where r is the radial distance from the scatterer to the observation point.

An automatic compact Schlieren imaging system for ultrasound transducer testing

The current standard used for the characterization of ultrasonic transducers is the hydrophonic technique, which is able to measure the acoustic pressure profile. This technique allows a quantitative analysis, but is marred by several problems. A scan of the region of interest is a time-consuming operation, especially when measuring a long acoustic beam. Furthermore, a hydrophone placed near the radiating surface is certainly an impediment to the free propagation of the field. Off-axis measurements can be inaccurate because of the angular response of the hydrophone. These problems, together with the costs, have encouraged the search for an alternative quick and inexpensive test system. The well-known Schlieren technique allows a real-time visualization of the whole pressure range of the transducers, but to display the entire beam emitted by the transducers it is necessary to use very large-diameter lenses, with focal lengths of several meters. Such systems are very cumbersome and difficult to use. The system developed in this paper allows the imaging of an acoustic beam up to 200 mm in length, but the system is compact, being only about 1 m long and 0.30 m wide. A similar system based on the classic Schlieren effect would be several meters long, with lenses of 200 mm in diameter. Finally, the system can reconstruct the section of the beam at any height, using an acoustic tomography technique, and can also implement a quantitative analysis. Because it uses only commercial components, the developed and fabricated ultrasonic beam analyzer is a very low-cost imaging system. The goal of this work is to create a compact, low-cost system based on this technique to test a wide range of ultrasonic transducers up to 40 MHz and above.

Detection of pith location in chestnut lumber (Castanea sativa Mill.) by means of acoustic tomography and longitudinal stress-wave velocity

The objective of this paper was to detect pith location in chestnut lumber by using acoustic tomography techniques. To this end, the velocity gradient was analysed by relating the value of longitudinal stress-wave velocity to the distance from the point where velocity was measured to the pith. A commercial stress-wave timer was used to measure longitudinal stress-wave velocity in 100 × 200 × 400 mm3 pieces of chestnut lumber (Castanea sativa Mill.) obtained from mature trees. The analysed pieces were conditioned to 20% moisture content. Results were classified according to the distance from the point at which velocity was measured to the pith. ANOVA revealed significant differences for mean velocity between the values obtained nearest the pith (at less than 40.0 mm) and the values obtained farthest from the pith. Velocity increased with distance to pith. The coefficient of determination for the linear regression between both variables was R2=0.96. The results of the tests showed a statistically significant relationship between longitudinal velocity and distance to pith. Such results allowed for the estimation of pith location in the area with the lowest velocity values.

Evaluation of Concrete Structures by the Acoustic Tomography Technique

This study is concerned with the acoustic tomography method, using measurements of primary wave (P-wave) travel time. In the first step, the principle of the technique is described. Then, the ability of this technique to assess the quality of concrete dams is discussed through two field surveys. It is shown that the acoustic tomography technique enables the evaluation of a large volume of material compared to other conventional nondestructive testing technologies. The benefit of this technique is more evident in identifying the location of anomalous zones that require further investigation and/or restoration work.

DISCRETE HUYGENS' MODEL APPROACH TO SOUND WAVE PROPAGATION—REVERBERATION IN A ROOM, SOUND SOURCE IDENTIFICATION AND TOMOGRAPHY IN TIME REVERSAL

This is a companion paper to our previous discrete Huyens' model approach to sound wave propagation. The validity and capability of the discrete Huygens' model or transmission-line modelling for the acoustical problems are discussed with applied examples. The acoustical response in a room for which the reverberation is characterized is simulated and a time-reversal approach to sound source identification and acoustic tomography technique is proposed. Some demonstrations are presented.

Testing of concrete in structures

According to the authors, “the principal aim of this book is to provide an overview of the subject for nonspecialist engineers who are responsible for the planning of test programs (p. III)” of hardened concrete in structures. The first edition of this book was published in 1982 and the second edition was published in 1989. Many developments have occurred since 1982, particularly in the field of in situ nondestructive testing. S.G. Millard joined Professor J.H. Bungey of the Department of Civil Engineering, University of Liverpool, in updating this third edition, which includes the description of many new developments and references. These are the contents: 1. Planning and interpretation of in situ testing (32 pages). This chapter is well documented. It describes the typical stages of the test program, presents in detail in situ concrete variability, and explains how to apply these results to specification and design calculations. Relevant British and American standards are listed, but it is essentially the British Standards that are considered in the remaining chapters. 2. Surface hardness methods (13 pages). This chapter concerns only the rebound principle; there is no mention of indentation testing, and penetration is discussed in Chapter 4. 3. Ultrasonic pulse velocity methods (35 pages). These methods are described in detail and the authors demonstrate a familiarity with techniques that are commonly applied in Canada. 4. Partially destructive strength tests (26 pages). This chapter deals with penetration resistance testing (Windsor probe and pin penetration), pull-out testing, pull-off testing, and break-off testing. Each test is well described and well illustrated. 5. Cores (18 pages). Here the authors discuss coring techniques, preparation of samples, and interpretation of the results, taking into account particularly the influence of the specimen’s size and elongation. 6. Load testing and monitoring (31 pages). In situ load testing is well illustrated as are the objectives of monitoring. However, the authors’ treatment of monitoring is somewhat superficial and unevenly balanced. Mechanical gauges are considered by them most suitable, which is no longer true since the development of automated data acquisition systems. Vibrating wire gauges are often preferred today. Apart from the consideration of optical fibre sensors, it would be pertinent to update this section of the book. 7. Durability tests (37 pages). These tests deal essentially with steel corrosion, moisture measurement, adsorption, and permeability tests. These tests are particularly detailed; however, the durability characterization requires a larger family of tests that are only superficially covered here and in Chapter 9. 8. Performance and integrity tests (31 pages). Important new techniques have developed in the past decade. Some of these new techniques presented here include radar, infrared thermography, x-ray, and gamma radiography. However, there is no mention of sonic or acoustic tomography techniques, although they are frequently applied to the evaluation of aged concrete dams. 9. Chemical testing and allied techniques (29 pages). These tests are related to the evaluation of the components of concrete (initial mix and environmental modifications) and specialized instrumental methods. Typical cases are presented in the appendix. The book includes over 300 references pertinent to each chapter. In conclusion, this book meets its objective of overviewing concrete testing in structures, and should be mandatory reading for every engineer planning in situ testing. However, it should be considered an introduction to be followed by more specialized books appropriate to one’s needs, particularly when monitoring structures and using tomographic techniques (integrity tests).

Sound Propagation Characteristics in Sound Fixing and Ranging Channel across Geostrophic Current

In order to develop ocean acoustic tomography techniques, it is very important to determine optimal receiving points and the propagation characteristics of sound in the SOFAR (SOund Fixing and Ranging) channel. We describe a preliminary computer simulation to estimate the sound arriving through a SOFAR channel across a geostrophic current. It is assumed that an ocean current is a geostrophic current and crosses the 1200 km propagation path at its center. Propagation times and detected pulsed sound waveforms are obtained in both directions of north-south propagation when the maximum flow speed changes from 0 to 153 cm/s. It is shown that a geostrophic current affects the propagation characteristics of sound. The difference in the propagation times for both directions can be used to estimate the flow speed along the propagation path.