6,102 research outputs found
Range-only underwater target localization : error characterization
Locating a target from range measurements
using only one mobile transducer has been increased
over the last years. This method allows us to reduce the
high costs of deployment and maintenance of
traditional fixed systems on the seafloor such as Long
Baseline. The range-only single-beacon is one of the
new architectures developed using the new capabilities
of modern acoustic underwater modems, which can be
time synchronization, time stamp, and range
measurements.
This document presents a method to estimate the
sources of error in this type of architecture so as to
obtain a mathematical model which allows us to
develop simulations and study the best localization
algorithms. Different simulations and real field tests
have been carried out in order to verify a good
performance of the model proposed.Postprint (published version
Low cost underwater acoustic localization
Over the course of the last decade, the cost of marine robotic platforms has
significantly decreased. In part this has lowered the barriers to entry of
exploring and monitoring larger areas of the earth's oceans. However, these
advances have been mostly focused on autonomous surface vehicles (ASVs) or
shallow water autonomous underwater vehicles (AUVs). One of the main drivers
for high cost in the deep water domain is the challenge of localizing such
vehicles using acoustics. A low cost one-way travel time underwater ranging
system is proposed to assist in localizing deep water submersibles. The system
consists of location aware anchor buoys at the surface and underwater nodes.
This paper presents a comparison of methods together with details on the
physical implementation to allow its integration into a deep sea micro AUV
currently in development. Additional simulation results show error reductions
by a factor of three.Comment: 73rd Meeting of the Acoustical Society of Americ
Laser Ultrasound Inspection Based on Wavelet Transform and Data Clustering for Defect Estimation in Metallic Samples
Laser-generated ultrasound is a modern non-destructive testing technique. It has been investigated over recent years as an alternative to classical ultrasonic methods, mainly in industrial maintenance and quality control procedures. In this study, the detection and reconstruction of internal defects in a metallic sample is performed by means of a time-frequency analysis of ultrasonic waves generated by a laser-induced thermal mechanism. In the proposed methodology, we used wavelet transform due to its multi-resolution time frequency characteristics. In order to isolate and estimate the corresponding time of flight of eventual ultrasonic echoes related to internal defects, a density-based spatial clustering was applied to the resulting time frequency maps. Using the laser scan beam’s position, the ultrasonic transducer’s location and the echoes’ arrival times were determined, the estimation of the defect’s position was carried out afterwards. Finally, clustering algorithms were applied to the resulting geometric solutions from the set of the laser scan points which was proposed to obtain a two-dimensional projection of the defect outline over the scan plane. The study demonstrates that the proposed method of wavelet transform ultrasonic imaging can be effectively applied to detect and size internal defects without any reference information, which represents a valuable outcome for various applications in the industry. View Full-TextPeer ReviewedPostprint (published version
Performance bounds on matched-field methods for source localization and estimation of ocean environmental parameters
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2001Matched-field methods concern estimation of source location and/or ocean environmental
parameters by exploiting full wave modeling of acoustic waveguide propagation.
Typical estimation performance demonstrates two fundamental limitations.
First, sidelobe ambiguities dominate the estimation at low signal-to-noise ratio (SNR),
leading to a threshold performance behavior. Second, most matched-field algorithms
show a strong sensitivity to environmental/system mismatch, introducing some biased
estimates at high SNR.
In this thesis, a quantitative approach for ambiguity analysis is developed so that
different mainlobe and sidelobe error contributions can be compared at different SNR
levels. Two large-error performance bounds, the Weiss-Weinstein bound (WWB)
and Ziv-Zakai bound (ZZB), are derived for the attainable accuracy of matched-field
methods. To include mismatch effects, a modified version of the ZZB is proposed.
Performance analyses are implemented for source localization under a typical shallow
water environment chosen from the Shallow Water Evaluation Cell Experiments
(SWellEX). The performance predictions describe the simulations of the maximum
likelihood estimator (MLE) well, including the mean square error in all SNR regions
as well as the bias at high SNR. The threshold SNR and bias predictions are also
verified by the SWellEX experimental data processing. These developments provide
tools to better understand some fundamental behaviors in matched-field performance
and provide benchmarks to which various ad hoc algorithms can be compared.Financial support for my research was provided by the Office of Naval Research
and the WHOI Education Office
Nonlinear time-warping made simple: a step-by-step tutorial on underwater acoustic modal separation with a single hydrophone
© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Bonnel, J., Thode, A., Wright, D., & Chapman, R. Nonlinear time-warping made simple: a step-by-step tutorial on underwater acoustic modal separation with a single hydrophone. The Journal of the Acoustical Society of America, 147(3), (2020): 1897, doi:10.1121/10.0000937.Classical ocean acoustic experiments involve the use of synchronized arrays of sensors. However, the need to cover large areas and/or the use of small robotic platforms has evoked interest in single-hydrophone processing methods for localizing a source or characterizing the propagation environment. One such processing method is “warping,” a non-linear, physics-based signal processing tool dedicated to decomposing multipath features of low-frequency transient signals (frequency f  1 km). Since its introduction to the underwater acoustics community in 2010, warping has been adopted in the ocean acoustics literature, mostly as a pre-processing method for single receiver geoacoustic inversion. Warping also has potential applications in other specialties, including bioacoustics; however, the technique can be daunting to many potential users unfamiliar with its intricacies. Consequently, this tutorial article covers basic warping theory, presents simulation examples, and provides practical experimental strategies. Accompanying supplementary material provides matlab code and simulated and experimental datasets for easy implementation of warping on both impulsive and frequency-modulated signals from both biotic and man-made sources. This combined material should provide interested readers with user-friendly resources for implementing warping methods into their own research.This work was supported by the Office of Naval Research (Task Force Ocean, project N00014-19-1-2627) and by the North Pacific Research Board (project 1810). Original warping developments were supported by the French Delegation Generale de l'Armement
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