Статті в журналах: "Acoustic thermometry. Speed of sound"

1

Dolgikh, Grigory, Yuri Morgunov, Alexander Burenin, Vladimir Bezotvetnykh, Vladimir Luchin, Aleksandr Golov, and Alexander Tagiltsev. "Methodology for the Practical Implementation of Monitoring Temperature Conditions over Vast Sea Areas Using Acoustic Thermometry." Journal of Marine Science and Engineering 11, no. 1 (January 6, 2023): 137. http://dx.doi.org/10.3390/jmse11010137.

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The methodological and technical possibilities of monitoring temperature fields in the Sea of Japan by acoustic thermometry methods are presented. The proposed tomographic method for monitoring the dynamics and structure of water is based on the transmission and reception of complex phase-shift keyed acoustic signals on a diagnosed track with the determination of the travel time along various ray trajectories, followed by the sound speed (temperature) determination. The physical prerequisites for the practical implementation of thermometric studies at large distances are based on the acoustic “mudslide” effect—the phenomenon of the acoustic energy “injection“ from the near-bottom shelf area to the underwater sound channel of the deep ocean. Based on the Sea of Japan example, an acoustic thermometry system based on tomographic schemes with mobile and stationary hydroacoustic sources for promising work in the field of oceanic climatology is proposed. For numerical calculations of the signal propagation channels’ impulse responses between sources and receivers, a specialized database of oceanological information was formed for the northwestern part of the Sea of Japan. The database includes all available data from organizations in Russia, Japan, North Korea, the Republic of Korea, and the United States (23,247 stations completed from 1925 to 2017). In the example of the Sea of Japan, a high-precision acoustic thermometry system based on tomographic schemes with developed mobile and stationary hydroacoustic transmitting and receiving systems was proposed and experimentally tested.

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2

Pisani, Marco, Milena Astrua, and Massimo Zucco. "Improved Acoustic Thermometry for Long-Distance Temperature Measurements." Sensors 23, no. 3 (February 2, 2023): 1638. http://dx.doi.org/10.3390/s23031638.

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Accurate measurements of long distances (in the order of tens of meters or more) are necessary in manufacturing processes of large structures, as, for example, in the aerospace industry. In the most demanding applications, the goal is to achieve a relative accuracy of 10−7 in the measurement of distances (e.g., 1 µm over 10 m). This goal can be obtained with laser interferometers whose accuracy is based on knowledge of the speed of light, which, in turn, depends on the temperature of air. A thermometer based on the measurement of the speed of sound in air has been realized at INRIM. Its purpose is the measurement of the air temperature along the measurement path of the interferometer with an accuracy of 0.1 °C at distances up to 11 m. The paper describes the principle and the experimental setup of the acoustic thermometer and demonstrates its performance by comparison with calibrated reference platinum resistance thermometers. Furthermore, we demonstrate the potentiality of the method to measure the vertical temperature gradient, which is the main error source in triangulation measurements when using laser trackers.

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3

Li, Shen, Wubin Weng, Chengdong Kong, Marcus Aldén, and Zhongshan Li. "Dual-Laser-Induced Breakdown Thermometry via Sound Speed Measurement: A New Procedure for Improved Spatiotemporal Resolution." Sensors 20, no. 10 (May 14, 2020): 2803. http://dx.doi.org/10.3390/s20102803.

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Measurement of acoustic waves from laser-induced breakdown has been developed as gas thermometry in combustion atmospheres. In the measurement, two laser-induced breakdown spots are generated and the local gas temperature between these two spots is determined through the measurement of the sound speed between them. In the previous study, it was found that the local gas breakdown can introduce notable system uncertainty, about 5% to the measured temperature. To eliminate the interference, in present work, a new measurement procedure was proposed, where two individual laser pulses with optimized firing order and delay time were employed. With the new measurement procedure, the system uncertainty caused by local gas breakdown can be largely avoided and the temporal and spatial resolutions can reach up to 0.5 ms and 10 mm, respectively. The improved thermometry, dual-laser-induced breakdown thermometry (DLIBT), was applied to measure temperatures of hot flue gases provided by a multijet burner. The measured temperatures covering the range between 1000 K and 2000 K were compared with the ones accurately obtained through the two-line atomic fluorescence (TLAF) thermometry with a measurement uncertainty of ~3%, and a very good agreement was obtained.

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4

Zhang, K., X. J. Feng, K. Gillis, M. Moldover, J. T. Zhang, H. Lin, J. F. Qu, and Y. N. Duan. "Acoustic and microwave tests in a cylindrical cavity for acoustic gas thermometry at high temperature." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 374, no. 2064 (March 28, 2016): 20150049. http://dx.doi.org/10.1098/rsta.2015.0049.

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Relative primary acoustic gas thermometry (AGT) determines the ratios of thermodynamic temperatures from measured ratios of acoustic and microwave resonance frequencies in a gas-filled metal cavity on isotherms of interest. When measured in a cavity with known dimensions, the frequencies of acoustic resonances in a gas determine the speed of sound, which is a known function of the thermodynamic temperature T . Changes in the dimensions of the cavity are measured using the frequencies of the cavity's microwave resonances. We explored techniques and materials for AGT at high temperatures using a cylindrical cavity with remote acoustic transducers. We used gas-filled ducts as acoustic waveguides to transmit sound between the cavity at high temperatures and the acoustic transducers at room temperature. We measured non-degenerate acoustic modes in a cylindrical cavity in the range 295 K< T <797 K. The fractional uncertainty of the measured acoustic frequencies increased from 2×10 −6 at 295 K to 5×10 −6 at 797 K. In addition, we measured the frequencies of several transverse magnetic (TM) microwave resonances up to 1000 K in order to track changes in the cavity's length L and radius R . The fractional standard deviation of the values of L deduced from three TM modes increased from 3×10 −6 for T <600 K to 57 × 10 −6 at 1000 K. We observed similar inconsistencies in a previous study.

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5

Kucukosmanoglu, Murat, John A. Colosi, Christopher W. Miller, Peter F. Worcester, and Matthew A. Dzieciuch. "The Beaufort Sea acoustic duct's variability and its impact on acoustic propagation using the mode interaction parameter." Journal of the Acoustical Society of America 151, no. 4 (April 2022): A48—A49. http://dx.doi.org/10.1121/10.0010620.

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The Beaufort duct is a subsurface sound channel formed by cold Pacific Winter Water sandwiched between warmer Pacific Summer Water and Atlantic Water in the Western Arctic Ocean. This duct traps sound waves and allows them to travel long distances without losing energy to lossy interactions with sea ice and surface waves. This study quantifies Beaufort duct variability based on Canada Basin Acoustic Propagation Experiment (CANAPE) and Coordinated Arctic Acoustic Thermometry Experiment (CAATEX) oceanographic observations. Deterministic ocean features induce coupling between acoustic modes confined to the Beaufort duct and non-ducted modes by weakening the duct or causing it to take on an asymmetric form. A non-dimensional mode interaction parameter (MIP) can be defined using the acoustic frequency and the vertical and horizontal scales of sound speed perturbation to characterize coupling strength. It identifies three important wave propagation regimes: sudden approximation, adiabatic approximation, and maximum interaction regime (Colosi and Zinicola-Lapin, 2021). When the MIP between ducted and lossy modes is more and less than 1, strong and weak acoustic variability is predicted, respectively. Variability is high when the MIP between two ducted modes surpasses 1, but modei–mode interference patterns grow more complicated. Acoustic numerical simulations are used to demonstrate various effects.

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6

Krolik, Jeffrey L., and Sunil Narasimhan. "Performance bounds on acoustic thermometry of ocean climate in the presence of mesoscale sound‐speed variability." Journal of the Acoustical Society of America 99, no. 1 (January 1996): 254–65. http://dx.doi.org/10.1121/1.414536.

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7

Krolik, Jeffrey L., and Sunil Narasimhan. "Performance limits on acoustic thermometry of ocean climate in the presence of mesoscale sound‐speed variability." Journal of the Acoustical Society of America 96, no. 5 (November 1994): 3236. http://dx.doi.org/10.1121/1.411123.

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8

Underwood, R., M. de Podesta, G. Sutton, L. Stanger, R. Rusby, P. Harris, P. Morantz, and G. Machin. "Estimates of the difference between thermodynamic temperature and the International Temperature Scale of 1990 in the range 118 K to 303 K." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 374, no. 2064 (March 28, 2016): 20150048. http://dx.doi.org/10.1098/rsta.2015.0048.

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Using exceptionally accurate measurements of the speed of sound in argon, we have made estimates of the difference between thermodynamic temperature, T , and the temperature estimated using the International Temperature Scale of 1990, T 90 , in the range 118 K to 303 K. Thermodynamic temperature was estimated using the technique of relative primary acoustic thermometry in the NPL-Cranfield combined microwave and acoustic resonator. Our values of ( T − T 90 ) agree well with most recent estimates, but because we have taken data at closely spaced temperature intervals, the data reveal previously unseen detail. Most strikingly, we see undulations in ( T − T 90 ) below 273.16 K, and the discontinuity in the slope of ( T − T 90 ) at 273.16 K appears to have the opposite sign to that previously reported.

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9

Tavčar, Rok, Janko Drnovšek, Jovan Bojkovski, and Samo Beguš. "Optimization of a Single Tube Practical Acoustic Thermometer." Sensors 20, no. 5 (March 10, 2020): 1529. http://dx.doi.org/10.3390/s20051529.

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When designing a single tube practical acoustic thermometer (PAT), certain considerations should be addressed for optimal performance. This paper is concerned with the main issues involved in building a reliable PAT. It has to be emphasised that a PAT measures the ratio of the time delay between the single temperature calibration point (ice point) and any other temperature. Here, we present different models of the speed of sound in tubes, including the effects of real gases and an error analysis of the most accurate model with a Monte Carlo simulation. Additionally, we introduce the problem of acoustic signal overlap and some possible solutions, one of which is acoustic signal cancellation, which aims to eliminate the unwanted parts of an acoustic signal, and another is to optimize the tube length for the parameters of the gas used and specific temperature range.

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10

Gavioso, R. M., D. Madonna Ripa, C. Guianvarc’h, G. Benedetto, P. A. Giuliano Albo, R. Cuccaro, L. Pitre, and D. Truong. "Shell Perturbations of an Acoustic Thermometer Determined from Speed of Sound in Gas Mixtures." International Journal of Thermophysics 31, no. 8-9 (September 2010): 1739–48. http://dx.doi.org/10.1007/s10765-010-0831-8.

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11

Anand, Ajay, Ashwin Ramesh, Seungju Yeo, Narges Mohammadi, Mujdat Cetin, and Diane Dalecki. "Deep-learning based insitu ultrasound thermometry for thermal ablation monitoring." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A114. http://dx.doi.org/10.1121/10.0015724.

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Noninvasive in situ temperature measurement (thermometry) is an attractive means of mapping the region of thermal damage during thermal ablation treatments. Existing methods of ultrasound thermometry are ineffective beyond 50 °C due to multiple physical limitations, including a non-monotonic relationship between temperature and sound speed that reaches a plateau around 60 °C, tissue phase transitions and deformation. An ultrasound-based technology that can monitor treatment over the entire therapeutic temperature range is desirable clinically. This paper describes a deep learning-based approach that uses thermometry data from the periphery of the heating zone (where temperatures are less than 50 °C) to infer temperature throughout the treatment zone. Spatiotemporal 2D temperature maps from 3–12 s HIFU heating exposures (in 0.5 s increments) were generated (using COMSOL) with a subset used for training the network and the rest for testing. Peripheral temperature values (excluding the first 5 mm closest to the axial focus), scalar time values, and a binary flag indicating heating/cooling were inputs to the network, and the temperature profile axially through the HIFU focus was predicted. The temperature prediction accuracy was better than 0.5 °C during heating and cooling. This paper will also address robustness to noise in the input temperature measurements and discuss future directions including experiments with ultrasound backscatter data and strategies to explicitly incorporate heat diffusion physics into the learning paradigm.

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12

Wang, Zheng, Yanwen Wang, Mi Tian, and Jiaxing Shen. "HearFire." Proceedings of the ACM on Interactive, Mobile, Wearable and Ubiquitous Technologies 6, no. 4 (December 21, 2022): 1–25. http://dx.doi.org/10.1145/3569500.

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Indoor conflagration causes a large number of casualties and property losses worldwide every year. Yet existing indoor fire detection systems either suffer from short sensing range (e.g., ≤ 0.5m using a thermometer), susceptible to interferences (e.g., smoke detector) or high computational and deployment overhead (e.g., cameras, Wi-Fi). This paper proposes HearFire, a cost-effective, easy-to-use and timely room-scale fire detection system via acoustic sensing. HearFire consists of a collocated commodity speaker and microphone pair, which remotely senses fire by emitting inaudible sound waves. Unlike existing works that use signal reflection effect to fulfill acoustic sensing tasks, HearFire leverages sound absorption and sound speed variations to sense the fire due to unique physical properties of flame. Through a deep analysis of sound transmission, HearFire effectively achieves room-scale sensing by correlating the relationship between the transmission signal length and sensing distance. The transmission frame is carefully selected to expand sensing range and balance a series of practical factors that impact the system's performance. We further design a simple yet effective approach to remove the environmental interference caused by signal reflection by conducting a deep investigation into channel differences between sound reflection and sound absorption. Specifically, sound reflection results in a much more stable pattern in terms of signal energy than sound absorption, which can be exploited to differentiate the channel measurements caused by fire from other interferences. Extensive experiments demonstrate that HireFire enables a maximum 7m sensing range and achieves timely fire detection in indoor environments with up to 99.2% accuracy under different experiment configurations.

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13

Barclay, David R., S. B. Martin, Paul C. Hines, Pablo Borys, Calder L. Robinson, James Hamilton, and Terry Deveau. "Coupled modeling of the seasonal transmission loss in the Beaufort Sea." Journal of the Acoustical Society of America 151, no. 4 (April 2022): A48. http://dx.doi.org/10.1121/10.0010617.

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An eight-element drifting vertical line array was deployed overwinter 2019–20 in the Beaufort Sea to record transmissions from two moored 35 Hz sources deployed as part of the Coordinated Arctic Acoustic Thermometry Experiment (CAATEX), and seven 925 Hz sources deployed by the Arctic Mobile Observing Systems (AMOS) experiment. Transmissions were received every day on the array at ranges of 10 to 850 km. A probabilistic rough-ice canopy was integrated to a Parabolic Equation code to predict the propagation loss. Sound speed profiles and percent ice cover along the propagation paths were obtained at daily resolution from data-assimilative Global Ice Ocean Prediction System (GIOPS, 20 km spatial resolution). Sea ice roughness and keel properties are empirically determined from the GIOPS ice thickness. The ice roughness is generated using a random pulse-train model with a characteristic wavenumber spectrum slope determined by ice age. Empirical probability distributions of ice keel depth, slope, and spatial densities are used to randomly add keels. Spatial averaging is used to account for signal bandwidth and uncertainty in receiver positions. The environment files and modeling are performed in piece-wise steps to manage memory footprints over long ranges. Modeled propagation losses compare well with the data and reproduce the seasonal variability observed in the measured results.

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14

Dzieciuch, Matthew A., Hanne Sagen, Peter F. Worcester, Espen Storheim, John A. Colosi, Richard A. Krishfield, Stein Sandven, and Florian Geyer. "The coordinated arctic acoustic thermometry experiment—CAATEX." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A72. http://dx.doi.org/10.1121/10.0015587.

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The coordinated arctic acoustic thermometry experiment (CAATEX) was a joint U.S.-Norwegian trans-Arctic acoustic propagation experiment with a design comparable to the 1994 TransArctic Propagation (TAP) experiment. The goal was to measure the changes in low-frequency sound propagation due to changes in ocean heat content and salinity, and ice conditions. Two 35 Hz acoustic transceiver moorings, one in the Nansen Basin and one in the Beaufort Sea, were deployed along with four other receiving moorings. All six moorings were equipped with vertical hydrophone arrays, recording transmissions every 36 h from fall 2019 to fall 2020. Each mooring also recorded temperature and salinity time series along the vertical extent of the hydrophone arrays, ice thickness using an upward-looking sonar, and ocean bottom pressure. The acoustic travel-times allow comparison of present-day heat content to the 1994 measurement, but there are several other points of comparison that are sensitive to environmental changes. These include transmission loss, acoustic scattering, and the acoustic arrival structure. These measurements of ocean and ice processes, and the acoustic propagation and ambient sound will improve our ability to monitor, communicate, and navigate in the Arctic Ocean.

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15

Bianco, Michael, and Peter Gerstoft. "Compressive acoustic sound speed profile estimation." Journal of the Acoustical Society of America 139, no. 3 (March 2016): EL90—EL94. http://dx.doi.org/10.1121/1.4943784.

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16

Zhang, Shi Ping, Guo Qing Shen, and Lian Suo An. "Time Delay Estimation in Reverberant Environment Based on Acoustic Pyrometry." Applied Mechanics and Materials 635-637 (September 2014): 811–14. http://dx.doi.org/10.4028/www.scientific.net/amm.635-637.811.

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The acoustic thermometry has many advantages, compared with conventional methods of temperature measurements. For this technology, the sound field in normal temperature state of the boiler was simulated; acoustic source signal obtained the pseudo random sequence signal and time delay estimation selected the weighted cross-correlation method. Experiments show that when the boiler is not running, the sound field is enclosure sound field in the furnace. The weighted cross-correlation method can restrain the reverberation and obtain the accurate time delay estimation.

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17

Bianco, Michael J., and Peter Gerstoft. "Dictionary learning of acoustic sound speed profiles." Journal of the Acoustical Society of America 140, no. 4 (October 2016): 3054. http://dx.doi.org/10.1121/1.4969490.

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18

Tindle, C. T., and G.E.J. "ATOC and Other Acoustic Thermometry Observations In New Zealand." Marine Technology Society Journal 33, no. 1 (January 1, 1999): 55–60. http://dx.doi.org/10.4031/mtsj.33.1.7.

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A summary of participation of the New Zealand group in the ATOC (Acoustic Thermometry of Ocean Climate) program over a five year period is presented. Transmissions from Heard Island were observed in the Tasman Sea during the Heard Island Feasibility Test in 1991. The California-New Zealand underwater sound path was verified with explosive sources in 1992. Single hydrophone observations were made of transmissions to New Zealand from California from an electrically driven source first suspended beneath a floating platform in 1994 and later placed on the ocean bottom at Pioneer Seamount in 1995. Results from these experiments show that acoustic propagation to ranges of order 10 Mm appears to be characterised by large fluctuations occurring with a time scale of a few minutes.

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19

Costa, Daniel, Daniel Crocker, James Gedamke, Paul Webb, Burney Le Boeuf, Danielle Waples, Sean Hayes, and James Ganong. "Response of elephant seals to acoustic thermometry of ocean climate sound transmissions." Journal of the Acoustical Society of America 102, no. 5 (November 1997): 3177. http://dx.doi.org/10.1121/1.420823.

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20

Woolfe, Katherine F., Shane Lani, and Karim G. Sabra. "Passive acoustic thermometry of the deep water sound channel using ambient noise." Journal of the Acoustical Society of America 134, no. 5 (November 2013): 3983. http://dx.doi.org/10.1121/1.4830512.

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21

Bok Kyoung Choi and Suk Wang Yoon. "Acoustic bubble counting technique using sound speed extracted from sound attenuation." IEEE Journal of Oceanic Engineering 26, no. 1 (2001): 125–30. http://dx.doi.org/10.1109/48.917945.

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22

Saijo, Yoshifumi, Hidehiko Sasaki, Naohiro Hozumi, Kazuto Kobayashi, Motonao Tanaka, and Tomoyuki Yambe. "Sound speed scanning acoustic microscopy for biomedical applications." Technology and Health Care 13, no. 4 (July 25, 2005): 261–67. http://dx.doi.org/10.3233/thc-2005-13405.

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23

Bianco, Michael J., Haiqiang Niu, and Peter Gerstoft. "Compressive acoustic sound speed profile estimation using wavelets." Journal of the Acoustical Society of America 139, no. 4 (April 2016): 2167. http://dx.doi.org/10.1121/1.4950426.

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24

Emms, Grant W., Bernadette Nanayakkara, and Jonathan J. Harrington. "Application of longitudinal-wave time-of-flight sound speed measurement to Pinus radiata seedlings." Canadian Journal of Forest Research 43, no. 8 (August 2013): 750–56. http://dx.doi.org/10.1139/cjfr-2012-0482.

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The sound speed of wood is related to important wood quality properties such as the microfibril angle of the S2 layer in the cell wall, stiffness, and shrinkage propensity. Measuring the sound speed of seedling stems has benefits to the forestry industry, potentially enabling early selection of trees that yield better quality wood. A nondamaging longitudinal-wave time-of-flight (LWToF) acoustic technique was used to determine the sound speed of 10 cm long sections of 2-year-old Pinus radiata D. Don seedlings. The measured sections were harvested and acoustic resonance used to determine the sound speed of the sections before and after the bark was removed and after the remaining xylem was dried. A linear relationship between the acoustic resonance sound speed of the dry xylem and the LWToF sound speed of the seedling stem was found (R2 = 0.89). To demonstrate a potential application using the LWToF acoustic technique, it was used as a tool for investigating the effect of various applied stresses on wood properties of a clone of P. radiata. The LWToF sound speed measurements of phytohormone stressed stems were significantly lower than the control stems, indicating the negative impact on stiffness and shrinkage propensity imposed by this treatment.

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25

Rabenstein, Rudolf, and Paolo Annibale. "Acoustic Source Localization under Variable Speed of Sound Conditions." Wireless Communications and Mobile Computing 2017 (2017): 1–17. http://dx.doi.org/10.1155/2017/9524943.

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The rich literature on acoustic source localization mostly relies on the assumption of a constant value for the speed of sound. This hypothesis allows establishing simple relations between range differences and time differences and leads to effective estimation algorithms. However, it must be challenged for certain applications of wireless acoustic sensor networks in multizone buildings and outdoor environments. This article revisits the source localization problem for the more general case of an unknown value for the speed of sound. It reviews the physical foundations for the dependence of the speed of sound on the air temperature and presents the essential approaches to acoustic source localization. On this basis, several methods for source localization under uncertain or variable speed of sound conditions from the literature are discussed. Applications from different fields are shown. They comprise the localization of sources, sensors, and reflecting surfaces, time-difference-of-arrival disambiguation, and the direct determination of the speed of sound or the air temperature from acoustic measurements.

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26

Vazquez, Heriberto J., Bruce D. Cornuelle, Peter F. Worcester, and Matthew Dzieciuch. "Ocean acoustic tomography in the Beaufort Gyre." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A110. http://dx.doi.org/10.1121/10.0015713.

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An ocean acoustic tomography array with a radius of 150 km was installed in the central Beaufort Gyre during 2016–2017 for the Canada Basin Acoustic Propagation Experiment (CANAPE). Five transceivers were deployed in a pentagon shape with a sixth transceiver at the center and a long vertical receiving array northwest of the central mooring. At least 12 refracted-surface-reflected (RSR) ray arrivals with lower turning points at depths between 500 and 3500 m were resolved in the acoustic receptions at all receivers. Travel-time anomalies were computed relative to a range-dependent sound-speed reference made by objectively interpolating annual-average sound-speed profiles constructed from the temperature data at each mooring. The travel time anomalies were inverted to estimate the 3-D sound-speed anomaly, including corrections to the positions of sources and receivers consistent with the uncertainty from long-baseline acoustic navigation systems at each mooring. Although the deep water in the Canada Basin is nearly homogeneous in temperature and salinity and highly stable (slowly warming in response to geothermal heating), it proved necessary to allow for a sound-speed change in the deep ocean to obtain consistent inversions, suggesting that the sound-speed equation at high pressure and low temperature is in error by about 0.1–0.2 ms−1.

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27

Coelho, Emanuel F., Paul Hursky, and Kevin D. Heaney. "Non-intrusive mode based analyses to predict uncertainty in sound propagation in the ocean." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A156. http://dx.doi.org/10.1121/10.0015872.

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Ocean dynamics can result in significant sound speed variability that are not well captured by deterministic numerical models and can impact differently high to low frequency acoustic propagation and bottom interactions by constraining horizontal and vertical paths. Uncertainty in the sound speed can, therefore, cause inaccuracies in acoustic based tactical decision tools and severely impact the accuracy of algorithms using sound propagation to estimate ocean volume states (e.g., ocean tomography or data assimilation). In this work, we propose to use a non-intrusive Reduced Order Modelling solution that consists of building a dictionary of static modes from historical ocean simulations with different settings and resolutions and climatology to derive an expedite uncertainty model along a central deterministic forecast. The system will then, through Orthogonal Matching Pursuit along the dictionary, use the available ocean model-data mismatches and/or acoustic innovations (e.g., arrival numbers and times, acoustic energy distribution, etc.) to define an ensemble of possible sound speed volume distributions and associated acoustic propagation outcomes. We will show results using a simplified simulation experiment that extracts “observations” from a nature reference field to document the procedure and benchmark results to reconstruct 3D sound speed fields from ocean-acoustic measurements.

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28

Göksu, Hüseyin. "Engine Speed–Independent Acoustic Signature for Vehicles." Measurement and Control 51, no. 3-4 (April 2018): 94–103. http://dx.doi.org/10.1177/0020294018769080.

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A vehicle, when running, makes a complex sound emission from the engine, the exhaust, the air conditioner, and other mechanical parts. Analysis of this sound for the purpose of vehicle identification is an interesting practice which has security- and transportation-related applications. Engine speed variation, which causes shifts in the frequency content of the emissions, makes Fourier-based methods ineffective in terms of providing a stable signature for the vehicle. We search for an engine speed–independent acoustic signature for the vehicle, and for this purpose, we propose wavelet packet analysis rather than traditional time- or frequency-domain methods. Wavelet packet analysis, by providing arbitrary time–frequency resolution, enables analyzing signals of stationary and non-stationary nature. It has better time representation than Fourier analysis and better high-frequency resolution than wavelet analysis. Under varying engine speed, sound emissions are recorded from four cars and analyzed by wavelet packet analysis. Wavelet packet analysis subimages are further analyzed to obtain feature vectors in the form of log energy entropy, norm entropy, and energy. These feature vectors are fed into a classifier, multilayer perceptron, for evaluation. While norm entropy achieves a classification rate of 100%, log energy entropy and energy achieves classification rates of 99.26% and 97.79%, respectively. These results indicate that, wavelet packet analysis along with norm entropy and multilayer perceptron provides an accurate vehicle-specific acoustic signature independent of the engine speed.

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29

Erbe, Christine, David Peel, Joshua N. Smith, and Renee P. Schoeman. "Marine Acoustic Zones of Australia." Journal of Marine Science and Engineering 9, no. 3 (March 19, 2021): 340. http://dx.doi.org/10.3390/jmse9030340.

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Underwater sound is modelled and mapped for purposes ranging from localised environmental impact assessments of individual offshore developments to large-scale marine spatial planning. As the area to be modelled increases, so does the computational effort. The effort is more easily handled if broken down into smaller regions that could be modelled separately and their results merged. The goal of our study was to split the Australian maritime Exclusive Economic Zone (EEZ) into a set of smaller acoustic zones, whereby each zone is characterised by a set of environmental parameters that vary more across than within zones. The environmental parameters chosen reflect the hydroacoustic (e.g., water column sound speed profile), geoacoustic (e.g., sound speeds and absorption coefficients for compressional and shear waves), and bathymetric (i.e., seafloor depth and slope) parameters that directly affect the way in which sound propagates. We present a multivariate Gaussian mixture model, modified to handle input vectors (sound speed profiles) of variable length, and fitted by an expectation-maximization algorithm, that clustered the environmental parameters into 20 maritime acoustic zones corresponding to 28 geographically separated locations. Mean zone parameters and shape files are available for download. The zones may be used to map, for example, underwater sound from commercial shipping within the entire Australian EEZ.

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30

Martinelli, Sheri L. "Simulation of Propagating Acoustic Wavefronts with Random Sound Speed." Communications in Computational Physics 16, no. 4 (October 2014): 1081–101. http://dx.doi.org/10.4208/cicp.250913.080414a.

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AbstractA method for simulating acoustic wavefronts propagating under random sound speed conditions is presented. The approach applies a level set method to solve the Eikonal equation of high frequency acoustics for surfaces of constant phase, instead of tracing rays. The Lagrangian nature often makes full-field ray solutions difficult to reconstruct. The level set method captures multiple-valued solutions on a fixed grid. It is straightforward to represent other sources of uncertainty in the input data using this model, which has an advantage over Monte Carlo approaches in that it yields an expression for the solution as a function of random variables.

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31

Amromin, Eduard. "Acoustic waves in gas flows with sound speed discontinuities." Journal of Sound and Vibration 469 (March 2020): 115154. http://dx.doi.org/10.1016/j.jsv.2019.115154.

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32

Bhatt, EeShan C., and Henrik Schmidt. "Four dimensional sound speed environments in ocean acoustic simulations." Journal of the Acoustical Society of America 141, no. 5 (May 2017): 3753. http://dx.doi.org/10.1121/1.4988278.

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33

Svensson, Elin. "Inverting acoustic communication signals for the sound speed profile." Journal of the Acoustical Society of America 120, no. 3 (September 2006): 1347–55. http://dx.doi.org/10.1121/1.2234851.

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34

Richards, Edward, and John A. Colosi. "Viability of the mixed layer duct with observed dynamics." Journal of the Acoustical Society of America 151, no. 4 (April 2022): A49. http://dx.doi.org/10.1121/10.0010622.

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While the upper ocean of the north Pacific is largely mixed due to air-sea interaction, a 1000 km sea-soar transect shows the existence of stratification in the mixed layer that persists over many tens of kilometers. The effects of this stratification on mixed layer acoustic propagation depends on the sound speed differences across the different density layers, and observations show the sound speed varies rapidly both between and along the isopycnals. Acoustic models are used to separately quantify the importance of the mixed layer stratification and the density compensated sound speed variability on propagation in the mixed layer duct. The observed sound speed field is modeled as the superposition of three fields: a smooth background, the stratification field with slow isopycnal sound speed variability, and the remnant unstratified sound speed variation. The sound speed variation in the stratified mixed layer is attributed to internal waves and eddy filaments and in the unstratified field to ocean spice. Both types of observed sound speed variation significantly change, or completely block, mixed layer propagation. Examples are presented of blocking features in the tilt or spice fields separately, and where they exist only in the superposition of the two fields.

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35

Han, Jian, Yun Feng Wei, and Ying Huang. "Mechanism Study of Acoustics Method for Dryness Measuring and Model Establishment." Applied Mechanics and Materials 532 (February 2014): 96–101. http://dx.doi.org/10.4028/www.scientific.net/amm.532.96.

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Combining acoustic theory and thermodynamic properties of water and steam, the density and sound velocity change with pressure and temperature, and the acoustic wave at the same temperature, the same pressure of gas-liquid two phase flow in the corresponding content of different causes the sound speed change are studied.. Set up steam model formula and the speed of sound, results showed that, water and water vapor velocity and density affected by temperature, pressure changes are different, steam quality measurement by acoustic method is feasible.

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36

TAROUDAKIS, MICHAEL I., and JOHN S. PAPADAKIS. "A MODAL INVERSION SCHEME FOR OCEAN ACOUSTIC TOMOGRAPHY." Journal of Computational Acoustics 01, no. 04 (December 1993): 395–421. http://dx.doi.org/10.1142/s0218396x93000214.

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An inversion scheme based on normal-mode representation of the acoustic field is applied in ocean acoustic tomography for a range-dependent reconstruction of the sound speed variations at a vertical slice. The scheme is based on the assumption that modal phase can be measured by suitable mode filtering at some range from the sound source. Two cases have been considered. The first of them makes no use of oceanographic information on the variability to be recovered, while the second one makes use of empirical orthogonal functions (EOFs) that describe sound speed variations in the ocean. The data used in the applications presented in this paper are synthetic ones. It is shown that both modal inversion schemes can be used for the recovery of range-dependent sound speed variations of compact support in the ocean, provided that a range dependent background environment is used to describe an initial guess of the variations. The scheme is more powerful when EOFs are used.

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37

Jensen, Bjørn Christian Skov, and Kim Knudsen. "Sound speed uncertainty in acousto-electric tomography." Inverse Problems 37, no. 12 (November 26, 2021): 125011. http://dx.doi.org/10.1088/1361-6420/ac37f8.

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Abstract The goal in acousto-electric tomography is to reconstruct an image of the unknown electric conductivity inside an object from boundary measurements of electrostatic currents and voltages collected while the object is penetrated by propagating ultrasound waves. This problem is a coupled-physics inverse problem. Accurate knowledge of the propagating ultrasound wave is usually assumed and required, but in practice tracking the propagating wave is hard due to inexact knowledge of the interior acoustic properties of the object. In this work, we model uncertainty in the sound speed of the acoustic wave, and formulate a suitable reconstruction method for the interior power density and conductivity. We also establish theoretical error bounds, and show that the suggested approach can be understood as a regularization strategy for the inverse problem. Finally, we numerically simulate the sound speed variations from a numerical breast tissue model, and computationally explore the effect of using an inaccurate sound speed on the error in reconstructions. Our results show that with reasonable uncertainty in the sound speed reliable reconstruction is still possible.

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38

Guo, Miao, Yue Li, and Jingmin Gao. "Relative Humidity Measurement of Air in Low-Temperature Ranges Using Low-Frequency Acoustic Waves and Correlation Signal Processing Techniques." Sensors 22, no. 16 (August 19, 2022): 6238. http://dx.doi.org/10.3390/s22166238.

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Air relative humidity (RH) is an important control parameter in many industrial processes. The acoustic method is a novel technique to measure air humidity non-intrusively. Relevant research is limited. Existing methods use ultrasonic waves as a sound source and air humidity is measured by measuring the sound attenuation. In this paper, a novel air humidity measurement system using low-frequency sound waves as a sound source and two acoustic sensors is proposed. Air humidity is acquired by measuring sound speed in the air. Sound speed mainly depends on air temperature, humidity, atmospheric pressure, and air composition. The influence of air temperature, atmospheric pressure, and air constituent concentrations on the RH measurement is analyzed theoretically. A 0.1 s linear chirp signal in the frequency range of 200–500 Hz is selected as the sound source. Sound travel time is calculated by cross-correlating the sound signals received by the two acoustic sensors. To improve the accuracy of the sound speed measurement, sound speed under different RH points is obtained through reference RH experiments and substituted into the calibration equation. Then, equivalent sound path length and systematic delay are estimated using the least squares method. After obtaining these two parameter values, the sound speed measured by the system is closer to the theoretical value at the same RH point. In validation experiments using RH measured by a thermo-hygrometer as a comparison, the relative errors of the acoustically measured RH are within 9.9% in the RH range of 40.7–87.1%, and the standard deviation is within 4.8%.

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39

Masovic, Drasko, and Ennes Sarradj. "Derivation of Lighthill’s Eighth Power Law of an Aeroacoustic Quadrupole in Acoustic Spacetime." Acoustics 2, no. 3 (September 8, 2020): 666–73. http://dx.doi.org/10.3390/acoustics2030035.

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Acoustic spacetime is a four-dimensional manifold analogue to the relativistic spacetime with the reference speed of light replaced by the speed of sound. It has been established primarily for the indirect studies of relativistic phenomena by means of their better understood acoustic analogues. More recently, it has also been used for the analytical treatment of sound propagation in various uniform and non-uniform flows of the background fluid. In this paper the analogy is extended and utilized to derive Lighthill’s eight power law for sound generation of an aeroacoustic quadrupole. Adding to the existing analogue theory, propagating sound waves are described in terms of a weak perturbation of the background acoustic spacetime metric. The obtained result proves that the acoustic analogy can be extended to cover both weak perturbation of the fluid due to the sound waves and certain sound generation mechanisms, at least in incompressible low Mach number flows.

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40

Dall'Osto, David R., and Dajun Tang. "Acoustic resonances within the surficial layer of a muddy seabed." Journal of the Acoustical Society of America 151, no. 5 (May 2022): 3473–80. http://dx.doi.org/10.1121/10.0011472.

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This is an investigation of sound propagation over a muddy seabed at low grazing angles. Data were collected during the 2017 Seabed and Bottom Characterization Experiment, conducted on the New England Mud Patch, a 500 km2 area of the U.S. Eastern Continental Shelf characterized by a thick layer of muddy sediments. Sound Underwater Signals (SUS), model Mk64, were deployed at ranges of 1–15 km from a hydrophone positioned 1 m above the seafloor. SUS at the closest ranges provide measurements of the bottom reflection at low grazing angles (<3 deg). Broadband analysis from 10 Hz to 10 kHz reveals resonances in the bottom reflected signals. Comparison of the measurements to simulated signals suggest a surficial layer of mud with a sound speed lower than the underlying mud and overlying water. The low sound speed property at the water–mud interface, which persists for less than 1 m, establishes a sound duct that impacts mid-frequency sound propagation at low grazing angles. The presence of a low-speed surficial layer of mud could be universal to muddy seabeds and, hence, has strong implications for mid-frequency sound propagation wherever mud is present.

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41

Vecchiotti, Andrea, Hannah Blackburn, Kyle Kirian, Joseph Vignola, Diego Turo, Jeff Foeller, and Teresa J. Ryan. "Scanning Doppler LIDAR wind profiles to inform near shore atmospheric acoustic propagation modeling." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A57. http://dx.doi.org/10.1121/10.0015531.

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This work presents a comprehensive experimental system to measure concurrent atmospheric acoustic transmission loss and meteorological conditions. A three-dimensional scanning Doppler lidar wind profiler captures real-time wind speed gradients at many locations along the acoustic propagation path of a simple pitch catch style study. A long-range acoustic device on an anchored pontoon sends known chirp sequences to a seven-channel receiver array at the water’s edge at ranges up to approximately one kilometer. Additional synchronized meteorological observations include temperature, humidity, and wind measured with anemometers. The meteorological data stream is used to inform the sound speed gradient implemented in a parabolic equation based numerical model of atmospheric acoustic propagation. The model can account for sea surface roughness and accommodate a sound speed profile that changes along the propagation range. Model predictions are compared to measured transmission losses. An assessment of the value of the computational cost of incorporating the varying sound speed profiles in the model is presented.

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42

Lopez Case, Jade F., Andrew R. McNeese, Preston S. Wilson, James H. Miller, and Gopu R. Potty. "Acoustic modeling of ducted propagation in the New England Mud Patch." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A145. http://dx.doi.org/10.1121/10.0015840.

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Experiments were conducted on the New England Mud Patch in 2017, 2021, and 2022. The 2017 Seabed Characterization Experiment (SBCEX17) utilized Signal Underwater Sound (SUS) charges, model Mk64, to produce an impulsive acoustic waveform. However, recent work in 2022 has additionally utilized the Rupture Induced Underwater Sound Source (RIUSS) to produce a high-amplitude, broadband waveform with minimal bubble oscillations. Results from these experiments suggested the presence of a surficial layer of mud with a sound speed lower than that of the underlying mud and overlying water. The SBCEX22 experiment included the deployment of nine RIUSS devices and the use of Ocean Bottom Recorders (OBX) to measure the acoustic pressure and three components of particle velocity at range of about 1 km. Conductivity, temperature, and depth measurements from CTD surveys were taken from several locations around the mud patch and used to generate sound speed profiles. These were input into the RAM parabolic equation model to analyze the effect of the sound speed in mud on propagation. Results from the RAM modeling indicates that at mid-frequencies (1-3 kHz) the lower sound speed at the top of the mud layer creates a duct where the transmission loss is reduced.

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43

Sun, Guanwen, Hanyin Cui, Chao Li, Weijun Lin, and Chang Su. "Experimental and theoretical investigations of dispersion of ultrasonic waves in the low-temperature and low-pressure nitrogen gas." Journal of the Acoustical Society of America 153, no. 2 (February 2023): 821–34. http://dx.doi.org/10.1121/10.0017097.

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Temperature has a complex effect on acoustic dispersion in dilute gases. In this paper, the effect of temperature on the acoustic dispersion of dilute gases is analyzed theoretically and experimentally. Theoretically, the Navier–Stokes (NS) equation and the Greenspan's theory, which includes the rotational-relaxation correction, are applied to calculate the dispersive sound speed. It is concluded that the temperature affects the molecular translational relaxation and the rotational relaxation by influencing the average molecular collision frequency and the relaxation collision number, respectively, and thus, change the amplitude of the acoustic dispersion. Numerical calculations led to the conclusion that both translational and rotational dispersions weakened as the temperature decreased. Experimentally, sound speed measurements of 21–40 kHz acoustic waves were also carried out in gaseous nitrogen at temperatures ranging from −70 °C to 20 °C and pressures of 150–105 Pa. Theoretical predications indicate that the speed of sound should increase with decreasing pressure at all temperatures, and the degree of dispersion should diminish at lower temperatures. The experimental observation of dispersion is consistent with theory within experimental error (1%) but was not able to distinguish the small (0.01%) increase in sound speed expected at 150 Pa.

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44

Hursky, Paul, Emanuel F. Coelho, and Pierre F. Lermusiaux. "Improved acoustic situation awareness using reduced order models of ocean circulation." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A158. http://dx.doi.org/10.1121/10.0015878.

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Acoustic situation awareness consists of knowing how far own sensors can detect other platforms and how detectable your platform is to their sensors. Since acoustic propagation is reciprocal, differences are down to source levels produced by each platform, transmission loss between them (reciprocal), the relative sensitivity of sensors, and the different directional noise observed at each platform. Noise fields are due to sources present both in the neighborhood (nearby ships) and in distant hubs (harbor shipping). Acoustic propagation models are used to predict transmission loss and received levels at all locations. Such models use sound speed for inputs. Platforms with limited communications can only be updated with the best available sound speed forecasts and measurements on a sporadic basis. We have developed reduced order models for sound speed, which consist of pre-loaded basis sets that capture anticipated ocean state fluctuations, for which very small (easily communicated) sets of coefficients can be used to reconstruct 3D and 4D ocean fields (sound speed and currents) on remote or edge platforms. We will present examples in the simulation of how our reduced order models contribute to improved acoustic situational awareness on such platforms.

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45

Postema, Michiel, Christine Gering, Nicole Anderton, Craig S. Carlson, and Minna Kellomäki. "Monitoring the gelation of gellan gum with torsion rheometry and brightness-mode ultrasound." Current Directions in Biomedical Engineering 8, no. 2 (August 1, 2022): 33–36. http://dx.doi.org/10.1515/cdbme-2022-1010.

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Abstract Gellan gum is a hydrogel with several applications in ultrasonic imaging, novel drug delivery, and tissue regeneration. As hydrogels are dynamic entities, their viscocelastic and therefore their acoustic properties change over time, which is of interest to monitor. To determine the speed of sound from brightness-mode images, however, rather large quantities of hydrogel are needed. In this study, we investigated torsion rheometry as a means to determine acoustic properties. Perceived speeds of sound were derived and computed from torsion rheometry measurements of gelating gellan gum mixed with spermidine trihydrochloride crosslinker. For comparison, brightness-mode ultrasonic images were recorded of the same material inside a phantom well. The rheometry data converged to a speed of sound within a standard devitation of the speed of sound measured from the brightness-mode images.We have shown that dynamic acoustic properties of gelating gellan gum can be simulated and experimentally determined using torsion rheometry.

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46

Yan, Kaizhuang, Yongxian Wang, and Wenbin Xiao. "A New Compression and Storage Method for High-Resolution SSP Data Based-on Dictionary Learning." Journal of Marine Science and Engineering 10, no. 8 (August 10, 2022): 1095. http://dx.doi.org/10.3390/jmse10081095.

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The sound speed profile data of seawater provide an important basis for carrying out underwater acoustic modeling and analysis, sonar performance evaluation, and underwater acoustic assistant decision-making. The data volume of the high-resolution sound speed profile is vast, and the demand for data storage space is high, which severely limits the analysis and application of the high-resolution sound speed profile data in the field of marine acoustics. This paper uses the dictionary learning method to achieve sparse coding of the high-resolution sound speed profile and uses a compressed sparse row method to compress and store the sparse characteristics of the data matrix. The influence of related parameters on the compression rate and recovery data error is analyzed and discussed, as are different scenarios and the difference in compression processing methods. Through comparative experiments, the average error of the sound speed profile data compressed is less than 0.5 m/s, the maximum error is less than 3 m/s, and the data volume is about 10% to 15% of the original data volume. This method significantly reduces the storage capacity of high-resolution sound speed profile data and ensures the accuracy of the data, providing technical support for efficient and convenient access to high-resolution sound speed profiles.

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47

Desrochers, Jessica, Lora Van Uffelen, Sarah E. Webster, Alexander P. Muniz, Cristian E. Graupe, and Luis O. Pomales Velázquez. "Low-order acoustic mode arrivals in the Beaufort Duct." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A213. http://dx.doi.org/10.1121/10.0016050.

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Significant changes in the stratification of the Beaufort Sea over the last few decades have produced a subsurface duct located between 100- and 300-meters depth, known as the Beaufort Duct. This subsurface duct allows for long-range acoustic transmission with little to no interaction with the sea surface or seafloor. In August and September of 2017, acoustic transmissions from five active moored tomography sources were collected at ranges up to 530 km by two Seagliders along with in-situ environmental measurements. Sound-speed profiles from the Seaglider data were used as input for parabolic equation and normal mode predictions. Both the predictions and recorded acoustic data show a peak acoustic arrival prior to the final cutoff. We refer to this as a “foldover” feature in the acoustic timefront, and it can be connected back to the unique ducting features in the input sound speed profiles. The relationship between the extent of the foldover and the shape of the sound-speed profile in the duct is explored using normal modes. Modal group speed predictions for the low-order modes are used to understand which modes make up the foldover feature present in the acoustic timefront and to interpret the acoustic arrival patterns measured on the Seagliders.

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48

Storheim, Espen, Hanne Sagen, Matthew A. Dzieciuch, and Peter F. Worcester. "Modelling of sound propagation across the Arctic Ocean using oceanographic fields and oceanographic data." Journal of the Acoustical Society of America 152, no. 4 (October 2022): A73. http://dx.doi.org/10.1121/10.0015588.

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During the coordinated arctic acoustic thermometry experiment (CAATEX), two acoustic sources transmitted 35 Hz binary m-sequences in a yearlong experiment. The signals were transmitted across the Arctic Ocean and detected at distances up to 2700 km. The aim was to make measurements similar to those carried out in 1994 and 1998, to investigate the changes in sound propagation due to changes in the ocean temperature, ocean stratification, and thinning of the sea ice. Changes in propagation conditions over the last decades were investigated using time-series of data from ocean reanalysis, as well as available oceanographic data along the transect. Range-dependent fields were constructed and used as environmental input to acoustic models to produce time series of arrival times and vertical arrival structure. This approach allows for an examination of the sensitivity of low-frequency sound propagation to both vertical and large-scale horizontal changes in the ice-ocean environment. The predicted time series of acoustic travel times and arrival structure will be presented and compared with the observations.

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49

Campos, L. M. B. C., and M. H. Kobayashi. "On the Propagation of Sound in a High-Speed Non-Isothermal Shear Flow." International Journal of Aeroacoustics 8, no. 3 (May 2009): 199–230. http://dx.doi.org/10.1260/147547208786940035.

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The propagation of sound in shear flows is relevant to the acoustics of wall and duct boundary layers, and to jet shear layers. The acoustic wave equation in a shear flow has been solved exactly only for a plane unidirectional homentropic mean shear flow, in the case of three velocity profiles: linear, exponential and hyperbolic tangent. The assumption of homentropic mean flow restricts application to isothermal shear flows. In the present paper the wave equation in an plane unidirectional shear flow with a linear velocity profile is solved in an isentropic non-homentropic case, which allows for the presence of transverse temperature gradients associated with the ***non-uniform sound speed. The sound speed profile is specified by the condition of constant enthalpy, i.e. homenergetic shear flow. In this case the acoustic wave equation has three singularities at finite distance (besides the point at infinity), viz. the critical layer where the Doppler shifted frequency vanishes, and the critical flow points where the sound speed vanishes. By matching pairs of solutions around the singular and regular points, the amplitude and phase of the acoustic pressure in calculated and plotted for several combinations of wavelength and wave frequency, mean flow vorticity and sound speed, demonstrating, among others, some cases of sound suppression at the critical layer.

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50

DE MARINIS, ENRICO, PAOLA PICCO, and ROBERTO MELONI. "Monitoring polynyas with Ocean Acoustic Tomography: a feasibility study in Terra Nova Bay." Antarctic Science 15, no. 1 (February 19, 2003): 63–75. http://dx.doi.org/10.1017/s0954102003001068.

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This study looks at the feasibility of using Ocean Acoustic Tomography for long-term monitoring of polynyas using both observations in Terra Nova Bay polynya (Ross Sea) and simulations with a range dependent, multi-layered adiabatic normal mode acoustic propagation model. The summer sound speed profile is characterized by surface values of around 1450 m s−1, a minimum of 1441 m s−1 around 50 m depth and a linear increase with a 0.016 s−1 slope. Thus, the sound propagation is apparently ducted in the near surface layer and is refracted upward below it. During winter, due to water cooling and mixing processes, the subsurface minimum disappears, the surface sound speed is about 1440 m s−1 and no near surface layer ducted propagation occurs. Because of the specificity of the Terra Nova Bay seasonal sound speed profile and to cope with both deep and shelf water applicability, the feasibility study of acoustic inversion was undertaken using normal mode Match Field Tomography instead of the more classical travel-time inversion. The results from simulations demonstrate that ocean acoustic tomography is able to reproduce quite well the vertical sound speed profile, in particular the temporal evolution of summer stratification and winter mixing processes, thus providing information on the upper layer, where direct measurements are not possible.

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