934 research outputs found
Vector sensors for underwater : acoustic communications
Acoustic vector sensors measure acoustic pressure and directional components separately.
A claimed advantage of vector sensors over pressure-only arrays is the directional information
in a collocated device, making it an attractive option for size-restricted applications.
The employment of vector sensors as a receiver for underwater communications is relatively
new, where the inherent directionality, usually related to particle velocity, is used
for signal-to-noise gain and intersymbol interference mitigation. The fundamental question
is how to use vector sensor directional components to bene t communications, which
this work seeks to answer and to which it contributes by performing: analysis of acoustic
pressure and particle velocity components; comparison of vector sensor receiver structures
exploring beamforming and diversity; quanti cation of adapted receiver structures in distinct
acoustic scenarios and using di erent types of vector sensors. Analytic expressions
are shown for pressure and particle velocity channels, revealing extreme cases of correlation
between vector sensors' components. Based on the correlation hypothesis, receiver
structures are tested with simulated and experimental data. In a rst approach, called
vector sensor passive time-reversal, we take advantage of the channel diversity provided
by the inherent directivity of vector sensors' components. In a second approach named
vector sensor beam steering, pressure and particle velocity components are combined, resulting
in a steered beam for a speci c direction. At last, a joint beam steering and
passive time-reversal is proposed, adapted for vector sensors. Tested with two distinct
experimental datasets, where vector sensors are either positioned on the bottom or tied
to a vessel, a broad performance comparison shows the potential of each receiver structure.
Analysis of results suggests that the beam steering structure is preferable for shorter
source-receiver ranges, whereas the passive time-reversal is preferable for longer ranges.
Results show that the joint beam steering and passive time-reversal is the best option to
reduce communication error with robustness along the range.Sensores vetoriais acústicos (em inglês, acoustic vector sensors) são dispositivos que
medem, alem da pressão acústica, a velocidade de partÃcula. Esta ultima, é uma medida que
se refere a um eixo, portando, esta associada a uma direção. Ao combinar pressão acústica
com componentes de velocidade de partÃcula pode-se estimar a direção de uma fonte sonora
utilizando apenas um sensor vetorial. Na realidade, \um" sensor vetorial é composto de um
sensor de pressão (hidrofone) e um ou mais sensores que medem componentes da velocidade
de partÃcula. Como podemos notar, o aspecto inovador está na medição da velocidade de
partÃcula, dado que os hidrofones já são conhecidos.(...)This PhD thesis was supported by the Brazilian Navy Postgraduate Study Abroad
Program Port. 227/MB-14/08/2019
Advances in Sonar Technology
The demand to explore the largest and also one of the richest parts of our planet, the advances in signal processing promoted by an exponential growth in computation power and a thorough study of sound propagation in the underwater realm, have lead to remarkable advances in sonar technology in the last years.The work on hand is a sum of knowledge of several authors who contributed in various aspects of sonar technology. This book intends to give a broad overview of the advances in sonar technology of the last years that resulted from the research effort of the authors in both sonar systems and their applications. It is intended for scientist and engineers from a variety of backgrounds and even those that never had contact with sonar technology before will find an easy introduction with the topics and principles exposed here
A code-division, multiple beam sonar imaging system
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1989In this thesis, a new active sonar imaging concept is explored using the principle
of code-division and the simultaneous transmission of multiple coded signals. The signals
are sixteen symbol, four-bit, non-linear, block Frequency-Shift Keyed (FSK)
codes, each of which is projected into a different direction. Upon reception of the reflected
waveform, each signal is separately detected and the results are inverted to yield
an estimation of the spatial location of an object in three dimensions. The code-division
sonar is particularly effective operating in situations where the phase of the transmitted
signal is perturbed by the propagation media and the target Most imaging techniques
presently used rely on preservation of the phase of the received signal over the dimension
of the receiving array. In the code-division sonar, spatial resolution is obtained by
using the combined effects of code-to-code rejection and the a-priori knowledge of
which direction each code was transmitted. The coded signals are shown to be highly
tolerable of phase distortion over the duration of the transmission. The result is a high-resolution,
three-dimensional image, obtainable in a highly perturbative environment
Additionally, the code-division sonar is capable of a high frame rate due to the simplicity
of the processing required. Two algorithms are presented which estimate the spatial
coordinates of an object in the ensonified aperture of the system, and the performance of
the two is compared for different signal to noise levels. Finally, the concept of code-division
imaging is employed in a series of experiments in which a code-division sonar
was used to image objects under a variety of conditions. The results of the experiments
are presented, showing the resolution capabilities of the system
The significance of passive acoustic array-configurations on sperm whale range estimation when using the hyperbolic algorithm
In cetacean monitoring for population estimation, behavioural studies or mitigation,
traditional visual observations are being augmented by the use of Passive Acoustic
Monitoring (PAM) techniques that use the creature’s vocalisations for localisation.
The design of hydrophone configurations is evaluated for sperm whale (Physeter
macrocephalus) range estimation to meet the requirements of the current mitigation
regulations for a safety zone and behaviour research.
This thesis uses the Time Difference of Arrival (TDOA) of cetacean vocalisations with a
three-dimensional hyperbolic localisation algorithm. A MATLAB simulator has been
developed to model array-configurations and to assess their performance in source
range estimation for both homogeneous and non-homogeneous sound speed profiles
(SSP). The non-homogeneous medium is modelled on a Bellhop ray trace model, using
data collected from the Gulf of Mexico. The sperm whale clicks are chosen as an
exemplar of a distinctive underwater sound.
The simulator is tested with a separate synthetic source generator which produced a set
of TDOAs from a known source location. The performance in source range estimation
for Square, Trapezium, Triangular, Shifted-pair and Y-shape geometries is tested. The
Y-shape geometry, with four elements and aperture-length of 120m, is the most
accurate, giving an error of ±10m over slant ranges of 500m in a homogeneous medium,
and 300m in a non-homogeneous medium. However, for towed array deployments, the
Y-shape array is sensitive to angle-positioning-error when the geometry is seriously
distorted. The Shifted-pair geometry overcomes these limits, performing an initial
accuracy of ±30m when the vessel either moves in a straight line or turns to port or
starboard. It constitutes a recommendable array-configuration for towed array
deployments.
The thesis demonstrates that the number of receivers, the array-geometry and the arrayaperture
are important parameters to consider when designing and deploying a
hydrophone array. It is shown that certain array-configurations can significantly
improve the accuracy of source range estimation. Recommendations are made
concerning preferred array-configurations for use with PAM systems
Adaptive Bayesian Beamforming for Imaging by Marginalizing the Speed of Sound
Imaging methods based on array signal processing often require a fixed
propagation speed of the medium, or speed of sound (SoS) for methods based on
acoustic signals. The resolution of the images formed using these methods is
strongly affected by the assumed SoS, which, due to multipath, nonlinear
propagation, and non-uniform mediums, is challenging at best to select. In this
letter, we propose a Bayesian approach to marginalize the influence of the SoS
on beamformers for imaging. We adapt Bayesian direction-of-arrival estimation
to an imaging setting and integrate a popular minimum variance beamformer over
the posterior of the SoS. To solve the Bayesian integral efficiently, we use
numerical Gauss quadrature. We apply our beamforming approach to shallow water
sonar imaging where multipath and nonlinear propagation is abundant. We compare
against the minimum variance distortionless response (MVDR) beamformer and
demonstrate that its Bayesian counterpart achieves improved range and azimuthal
resolution while effectively suppressing multipath artifacts
Algorithms for propagation-aware underwater ranging and localization
Mención Internacional en el tÃtulo de doctorWhile oceans occupy most of our planet, their exploration and conservation are one of
the crucial research problems of modern time. Underwater localization stands among the
key issues on the way to the proper inspection and monitoring of this significant part of our
world. In this thesis, we investigate and tackle different challenges related to underwater
ranging and localization. In particular, we focus on algorithms that consider underwater
acoustic channel properties. This group of algorithms utilizes additional information
about the environment and its impact on acoustic signal propagation, in order to improve
the accuracy of location estimates, or to achieve a reduced complexity, or a reduced
amount of resources (e.g., anchor nodes) compared to traditional algorithms.
First, we tackle the problem of passive range estimation using the differences in the
times of arrival of multipath replicas of a transmitted acoustic signal. This is a costand
energy- effective algorithm that can be used for the localization of autonomous
underwater vehicles (AUVs), and utilizes information about signal propagation. We study
the accuracy of this method in the simplified case of constant sound speed profile (SSP)
and compare it to a more realistic case with various non-constant SSP. We also propose
an auxiliary quantity called effective sound speed. This quantity, when modeling acoustic
propagation via ray models, takes into account the difference between rectilinear and
non-rectilinear sound ray paths. According to our evaluation, this offers improved range
estimation results with respect to standard algorithms that consider the actual value of
the speed of sound.
We then propose an algorithm suitable for the non-invasive tracking of AUVs or
vocalizing marine animals, using only a single receiver. This algorithm evaluates the
underwater acoustic channel impulse response differences induced by a diverse sea
bottom profile, and proposes a computationally- and energy-efficient solution for passive
localization.
Finally, we propose another algorithm to solve the issue of 3D acoustic localization
and tracking of marine fauna. To reach the expected degree of accuracy, more sensors
are often required than are available in typical commercial off-the-shelf (COTS) phased
arrays found, e.g., in ultra short baseline (USBL) systems. Direct combination of multiple
COTS arrays may be constrained by array body elements, and lead to breaking the optimal array element spacing, or the desired array layout. Thus, the application of
state-of-the-art direction of arrival (DoA) estimation algorithms may not be possible. We
propose a solution for passive 3D localization and tracking using a wideband acoustic
array of arbitrary shape, and validate the algorithm in multiple experiments, involving
both active and passive targets.Part of the research in this thesis has been supported by the EU H2020 program under
project SYMBIOSIS (G.A. no. 773753).This work has been supported by IMDEA Networks InstitutePrograma de Doctorado en IngenierÃa Telemática por la Universidad Carlos III de MadridPresidente: Paul Daniel Mitchell.- Secretario: Antonio Fernández Anta.- Vocal: Santiago Zazo Bell
ON-ICE DETECTION, CLASSIFICATION, LOCALIZATION AND TRACKING OF ANTHROPOGENIC ACOUSTIC SOURCES WITH MACHINE LEARNING
Arctic acoustics have been of concern in recent years for the US navy. First-year ice is now the prevalent factor in ice coverage in the Arctic, which changes the previously understood acoustic properties. Due to the ice melting each year, anthropogenic sources in the Arctic region are more common: military exercises, shipping, and tourism. For the navy, it is of interest to detect, classify, localize, and track these sources to have situational awareness of these surroundings. Because the sources are on-water or on-ice, acoustic radiation propagates at a longer distance and so acoustics are the method by which the sources are detected, classified, localized, and tracked. These methods are all part of sound navigation and ranging (SONAR). This dissertation describes algorithms which will better SONAR results without modification of the sensors or the environment and the process by which to arrive to this point. The focus is to use supervised machine learning algorithms to facilitate such technological enhancements. Specifically, neural networks analyze labeled experimental data from a first-year, shore-fast, shallow and narrow water environment. The experiments were conducted over the span of three years from 2019 to 2022, mostly during the months from January to March where ice formed over the Keweenaw Waterway at the Michigan Technological University. All experiments were conducted to analyze a passive acoustic source; that is, the source was non-cooperative and did not send any localizing pings for active SONAR. The experiments were recorded using an underwater pa-type acoustic vector sensor (AVS). The data and analysis were done intermittently to update any upcoming experiments with discrepancies found in the analysis to create a more generalized algorithm. The work in this dissertation focuses on two topics for passive SONAR: localization and classification. Because of the ``black box nature in machine learning, tracking the target source is an extension of localization and thought of as the same goal within machine learning. To introduce and verify the complexity of the testing environment, an underwater acoustic simulation is shown with Ray tracing and bathymetry data to compare with the experimental results used in machine learning. The focus of the algorithms is to produce the best results for the experiments and compare the results with traditional methods, such as a simulation or a linear Gaussian localization with a Kalman filter. Experiments studying neural network types have shown that the Vision Transformer (ViT) produces excellent results. The ViT is capable of analyzing acoustic intensity azimuthal spectrogram (azigram) data and localizing a moving target at high accuracy, and the ViT is capable of classifying multiple acoustic sources with the acoustic intensity magnitude spectrogram at high accuracy as well
Advanced perception, navigation and planning for autonomous in-water ship hull inspection
Inspection of ship hulls and marine structures using autonomous underwater vehicles has emerged as a unique and challenging application of robotics. The problem poses rich questions in physical design and operation, perception and navigation, and planning, driven by difficulties arising from the acoustic environment, poor water quality and the highly complex structures to be inspected. In this paper, we develop and apply algorithms for the central navigation and planning problems on ship hulls. These divide into two classes, suitable for the open, forward parts of a typical monohull, and for the complex areas around the shafting, propellers and rudders. On the open hull, we have integrated acoustic and visual mapping processes to achieve closed-loop control relative to features such as weld-lines and biofouling. In the complex area, we implemented new large-scale planning routines so as to achieve full imaging coverage of all the structures, at a high resolution. We demonstrate our approaches in recent operations on naval ships.United States. Office of Naval Research (Grant N00014-06-10043)United States. Office of Naval Research (Grant N00014-07-1-0791
- …