Application Of Acoustic Tomography Research Articles

Monitoring Thermal Exchange of Hot Water Mass via Underwater Acoustic Tomography with Inversion and Optimization Method

Thermal exchange of underwater water mass caused by marine heat wave is a hot point of research recently. In particular, because the water temperature observation along hot water mass transportation is hard work. Acoustic tomography is an advanced method to measure water temperature variations via sound signal transmission with multi-station network sensing. The 5 kHz frequency acoustic tomography used for observing water temperature variations caused by ocean heat waves is interesting work. In this paper, the numerical simulation of hot water mass is completed first, then floatation and diffusion of hot water mass in a simulation are monitored by acoustic tomography. A new inversion optimization method is proposed to obtain hot water mass transportation variations at two-dimensional temperature vertical profile. The proposed inversion method adds a regularized mode matrix and the optimization method adds the model correlation matrix to improve the results quality. The accuracy of inversion optimization results is compared and discussed, where the mean temperature error is less than 0.4 °C. Sensing water temperature variation of marine heat waves is verified via acoustic signal transmission and improved inversion optimization method. The water dynamical process observation is an application of acoustic tomography, which can be further used observe underwater environmental characteristics.

Coupled velocity and temperature acoustic tomography in heated high subsonic Mach number flows

The application of acoustic tomography (AT) for simultaneous velocity and static temperature estimation has generally been restricted to low subsonic Mach number applications due to the increased complexities associated with acoustic refraction, high computational resource requirements, and a limited range of practical applications. The current work describes a novel AT method for application in such conditions and presents the results of a proof of concept laboratory jet experiment. Using a traversed set of acoustic sound source and microphones, acoustic propagation time measurements were collected at Mach 0.48 and 0.72 jet conditions (with total temperatures of 675 K) along three azimuthal orientations and used to perform AT. A comparison of intrusive and non-intrusive measurements showed that a three orientation reconstruction could approximate jet plume size and location within 1/4th of the jet’s radius. Several sensitivity studies were conducted to assess the behavior and limitations of the proposed AT method. In particular, the effects of orientation count, reconstruction resolution, and displacement measurement errors were investigated. The findings of these sensitivity studies were used to make recommendations for future experiments. This application is the first time an acoustic method is used to non-intrusively and simultaneously measure jet velocity and static temperature distributions in high subsonic Mach number flows.

Ocean gliders as tools for acoustic tomography

Ocean gliders are capable and increasingly ubiquitous platforms for collecting oceanographic data such as temperature and salinity measurements. These data alone are useful for ocean acoustic tomography applications, but gliders equipped with acoustic receivers can also record transmissions from acoustic sources, potentially providing additional paths for tomographic inversions. There are challenges associated with the use of gliders as tomography receivers, however, notably the uncertainty in underwater glider position, which can lead to ambiguity between sound-speed and glider position. Glider-based acoustic receptions from moored tomography sources can provide range measurements to aid in subsea glider localization. These data can be used in post-processing for precise glider positioning and in real-time for glider navigation. The current state of the art will be reviewed, and preliminary results will be presented from an experiment in the Arctic Ocean, which seeks to use moored acoustic tomography source signals for both subsea glider positioning and real-time navigation, including navigation under ice. [Work sponsored by ONR.]

Recent progress in Taiwan on integrating moving vehicles for acoustic tomography applications

Coastal seas around Taiwan exhibit a wide variety of oceanographic processes associated with the complex bottom topography, tides, winds (monsoons and typhoons), the Kuroshio, and the others. Conventional oceanographic measurements (e.g., acoustic Doppler current profiler) do not provide a synoptic image of the dynamic processes unless a large number of instruments are deployed. Ocean Acoustic Tomography (OAT) is an effective method for mapping the time-evolving spatial distribution of ocean current and temperature. As illustrated by Cornuell et al. (1989), the small spatial scale of ocean features is resolved by incorporating a ship-towed transceiver to the moored transceiver array, referred to as moving ship tomography (MST). The MST technique is applied to the ocean current reconstruction in coastal seas around Taiwan and is extended by using an autonomous underwater vehicle (AUV) as an alternative carrier for the transceiver. This talk presents a brief summary of the recent experiments and our upcoming project. Included are 1) a series of current-mapping experiments integrating moving vehicles in shallow-water environments and 2) simulation study of MST for experiment design on mapping the Kuroshio-induced current wakes of Green Island southeast of Taiwan.

Application of acoustic tomography to reconstruct the horizontal flow velocity field in a shallow river

AbstractA novel acoustic tomographic measurement system capable of resolving sound travel time in extremely shallow rivers is introduced and the results of an extensive field measurements campaign are presented and further discussed. Acoustic pulses were transmitted over a wide frequency band of 20–35 kHz between eight transducers for about a week in a meandering reach of theBāsen River, Hiroshima, Japan. The purpose of the field experiment was validating the concept of acoustic tomography in rivers for visualizing current fields. The particular novelty of the experiment resides in its unusual tomographic features: subbasin scale (100 m × 270 m) and shallowness (0.5–3.0 m) of the physical domain, frequency of the transmitted acoustic signals (central frequency of 30 kHz), and the use of small sampling intervals (105 s). Inverse techniques with no a priori statistical information were used to estimate the depth‐average current velocity components from differential travel times. Zeroth‐order Tikhonov regularization, in conjunction with L‐curve method deployed to stabilize the solution and to determine the weighting factor appearing in the inverse analysis. Concurrent direct environmental measurements were provided in the form of ADCP readings close to the right and left bank. Very good agreement found between along‐channel velocities larger than 0.2 m/s obtained from the two techniques. Inverted quantities were, however, underestimated, perhaps due to vicinity of the ADCPs to the banks and strong effect of river geometry on the readings. In general, comparing the visualized currents with direct nodal measurements illustrate the plausibility of the tomographically reconstructed flow structures.

Application of Acoustic Tomography and Ultrasonic Waves to Estimate Stiffness Constants of Muiracatiara Brazilian Wood

Determination of the stiffness constants of Muiracatiara wood (Astronium lecointei) was performed using Fakopp 3D acoustic tomography and James V Mk II ultrasound devices. Specific gravity, moisture content, and compression perpendicular to grain tests followed standard Brazilian requirements. Statistical tests were calculated to 99% confidence intervals. Using Christoffel’s equation, equality between stiffness constants and static modulus of elasticity occurred only when using the acoustic tomography device. These results show the importance of the acoustic tomography device, not only to detect defects, but also in determining elastic constants of wood.

Variations of tomography signals in shallow water due to bottom topography irregularities

The paper presents a quantitative study of the effect of the bottom topography on the acoustic signals used in ocean acoustic tomography applications. The study is restricted to shallow water areas where the importance of the bottom boundary in modelling acoustic propagation is more pronounced. It is shown that significant variations of the signal are expected due to the presence of some local boundary irregularity, being of the same order as regards the «useful» variations used for the data inversions. It is concluded that an accurate bottom description is needed to be used in connection with an reliable model handling acoustic propagation in range-dependent environments for all ocean acoustic tomography applications

Frictional Formulations in Numerical Ocean Models and Their Effect on Simulated Acoustic Fields

Abstract This study has examined the effects of frictional formulations in numerical ocean models on simulated acoustic fields. Starting from the same initial state of a perturbation to a simple linear front, comparisons are made of numerically simulated frontal environments, with biharmonic and Laplacian (harmonic) friction operators, to describe subgrid-scale mixing. Using a just stable harmonic simulation as a “control” for the effects of small-scale processes (wavelength of order 10 km), comparisons of the energetics and spectra of the simulated environments have confirmed the effect of biharmonic friction in suppressing small-scale motion while maintaining the mesoscale. However, a new result concerns the impact of this scale selectivity on simulated underwater acoustic fields and the possible consequences of this for ocean forecast models and acoustic tomography applications. Acoustic effects have been quantified in terms of the differences in predicted sound intensity levels between harmonic and bi...

The effect of an El Niño/Southern Oscillation event on underwater sound propagation

From June 1981 through June 1984, 15 separate ocean cruises were made to the equatorial Pacific to collect hydrographic data at 85°W as part of a NOAA climate program. The most recent El Niño/Southern Oscillation (ENSO) event occurred during this period. Temperature and salinity data obtained during the cruises have been processed and merged with archival data to form a series of sound‐speed profiles which reflect the onset, evolution, and cessation of the ENSO event. By using computer models, with these profiles as input data, it is shown that propagation conditions fundamentally changed as a result to the ENSO event. Conditions which support a convergence‐zone structure for a shallow source disappeared during the event resulting in bottom‐limited propagation. While this severe change provides an opportunity to detect and monitor ENSO events using underwater sound, it prevents the straightforward application of acoustic tomography to obtain the temperature field and, hence, to study the dynamics of the event. For a source located at mid‐depth, however, tomographic techniques may be applicable since propagation conditions are not as changeable there.