Portland State University PDXScholar Dissertations and Theses Dissertations and Theses Summer 7-14-2014 Advances in Aquatic Target Localization with Passive Sonar John Thomas Gebbie Portland State University Let us know how access to this document benefits ouy . Follow this and additional works at: http://pdxscholar.library.pdx.edu/open_access_etds Part of the Electrical and Computer Engineering Commons Recommended Citation Gebbie, John Thomas, "Advances in Aquatic Target Localization with Passive Sonar" (2014). Dissertations and Theses. Paper 1932. 10.15760/etd.1931 This Dissertation is brought to you for free and open access. It has been accepted for inclusion in Dissertations and Theses by an authorized administrator of PDXScholar. For more information, please contact [email protected]. Advances in Aquatic Target Localization with Passive Sonar by John Thomas Gebbie A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering Dissertation Committee: T. Martin Siderius, Chair Lisa M. Zurk Richard L. Campbell John S. Allen, III Mark D. Sytsma Portland State University 2014 c 2014 John Gebbie Abstract New underwater passive sonar techniques are developed for enhancing target local- ization capabilities in shallow ocean environments. The ocean surface and the seabed act as acoustic mirrors that reflect sound created by boats or subsurface vehicles, which gives rise to echoes that can be heard by hydrophone receivers (underwater microphones). The goal of this work is to leverage this \multipath" phenomenon in new ways to determine the origin of the sound, and thus the location of the tar- get. However, this is difficult for propeller driven vehicles because the noise they produce is both random and continuous in time, which complicates its measurement and analysis. Further, autonomous underwater vehicles (AUVs) pose additional chal- lenges because very little is known about the sound they generate, and its similarity to that of boats. Existing methods for localizing propeller noise using multiple hy- drophones have approached the problem either purely theoretically, or empirically such as by analyzing the interference patterns between multipath arrivals at differ- ent frequencies, however little has been published on building localization techniques that directly measure and utilize the time delays between multipath arrivals while simultaneously accounting for relevant environmental parameters. This research de- velops such techniques through a combination of array beamforming and advanced ray-based modeling that account for variations in bathymetry (seabed topography) as well as variations of the sound speed of the water. The basis for these advances come from several at-sea experiments in which different configurations of passive sonar systems recorded sounds emitted by different types of targets, including small boats and an autonomous underwater vehicle. Ultimately, these contributions may reduce the complexity and cost of passive systems that need to be deployed close to shore, such as for harbor security applications. Further, they also create new possibilities i for applying passive sonar in remote ocean regions for tasks such as detecting illegal fishing activity. This dissertation makes three key contributions: 1. Analysis of the aspect-dependent acoustic radiation patterns of an underway autonomous underwater vehicle (AUV) through full-field wave modeling. 2. A two-hydrophone cross-correlation technique that leverages multipath as well as bathymetric variations to estimate the range and bearing of a small boat, supported by a mathematically rigorous performance analysis. 3. A multi-target localization technique based on directly measuring multipath from multiple small surface vessels using a small hydrophone array mounted to the nose of an AUV, which operates by cross-correlating two elevation beams on a single bearing. ii Dedication To Donald and Jo Anne, my parents. You always believed in me. To Tom, my uncle. You ignited my passion for science. To Tom, my brother. You have always been there for me. To Vanessa, the love of my life. You are my rock. iii Acknowledgements I would like to express my deep appreciation and gratitude to my advisor, Martin Siderius, for his constant encouragement, patience, and mentorship. Throughout the PhD program, not only have I been the beneficiary of his intellect and fantastic attitude, but his friendship as well. I consider myself truly fortunate to have had the opportunity to work with him. I would like to thank Lisa Zurk for initially recognizing that I belonged in this field, and for teaching me the how to think and speak like a scientist. I would like to thank John Allen for his advice, for making the Hawai`i experiments possible, and for his valuable feedback on my research. To my dissertation committee, Mark Sytsma, Richard Campbell, John Allen, and Lisa Zurk, thank you for your time and advice on how to strengthen my dissertation. To the many current and former colleagues I have had at the NEAR-Lab, thank you for your feedback, helpful conversations, and friendship. Finally, I would like to acknowledge and thank the Office of Naval Research for my fellowship, which has helped make this work possible. iv Table of Contents Abstracti Dedication iii Acknowledgements iv List of Tables viii List of Figures ix 1 Introduction1 2 Background 11 2.1 Harbor Security Threats......................... 13 2.2 Radiated Noise from AUVs........................ 18 2.3 Time Delay Localization......................... 22 2.3.1 Hyperbolic Fixing / Multilateration............... 23 2.3.2 Marine Mammal Localization.................. 25 2.3.3 Noise Source Localization.................... 30 2.4 Beamforming and Multipath....................... 34 2.4.1 Matched Field Processing.................... 36 2.4.2 Passive Fathometer........................ 38 2.5 Multipath Coherence and Waveguide Invariance............ 40 3 Theory 43 3.1 Signal Intensity Detection and Ranging................. 44 3.2 Signal Processing............................. 46 3.2.1 Fourier Analysis.......................... 47 3.2.2 Cross-Correlation......................... 48 3.2.3 Random Processes and Stationarity............... 51 3.2.4 Pre-Whitening.......................... 53 3.2.5 Time Delay Estimation...................... 55 3.3 The Wave Equation............................ 58 3.3.1 Continuity Equation (I)..................... 58 v 3.3.2 Equation of State (II)...................... 60 3.3.3 Equation of Motion (III)..................... 62 3.3.4 The Wave Equation........................ 64 3.4 Propagation Modeling.......................... 67 3.4.1 The Helmholtz Equation..................... 68 3.4.2 Overview of Common Models.................. 73 3.4.3 Wavenumber Integration..................... 73 3.4.4 Ray Tracing............................ 75 3.5 Spatial Filtering.............................. 78 3.5.1 Conventional Beamforming.................... 79 3.5.2 Adaptive Beamforming...................... 81 3.5.3 Matched Field Processing.................... 88 4 Line Array Processing 90 4.1 Hawai`i 2010 Experiment......................... 91 4.1.1 POEMS-A Hydrophone Arrays................. 92 4.1.2 REMUS-100 AUV........................ 96 4.2 Source Level Estimation Method.................... 102 4.3 Spectrograms............................... 102 4.4 Cross-correlation of Broadband Modem Noise............. 104 4.5 Genetic Algorithm for Array Element Localization........... 105 4.6 Bearing-Time-Record (BTR) of Narrowband Emissions........ 107 4.7 Tonal Peak Following........................... 108 4.8 Propagation Modeling of Narrowband Emissions............ 109 4.9 Aspect-Dependent Source Level Measurements............. 109 4.10 Scissorgrams................................ 112 4.11 Chapter Summary............................ 115 5 Two-Hydrophone Processing 118 5.1 Multipath Structure in Shallow Water................. 121 5.1.1 Cross-Correlation and Cross-Spectrum............. 125 5.2 Localization Algorithm.......................... 128 5.2.1 Acoustic Processing........................ 128 5.2.2 Ray Model Processing...................... 130 5.2.3 Ambiguity Surface for Target Location............. 130 5.3 Cram´er-RaoLower Bound on Range.................. 132 5.3.1 Simulation............................. 135 5.4 Array Side Discrimination........................ 137 5.4.1 Simulation............................. 142 5.5 Hawai`i 2011 Experiment......................... 145 5.6 Striation Extraction Particle Filtering.................. 148 5.7 Experimental Results........................... 151 vi 5.8 Chapter Summary............................ 155 6 Volumetric Array Processing 156 6.1 Problem Formulation........................... 160 6.2 Adaptive Beamforming.......................... 161 6.3 Cross Beam Correlation......................... 164 6.4 Target Localization Procedure...................... 166 6.5 GLASS'12 Experiment.......................... 168 6.5.1 Predicted Multipath Structure.................. 176 6.6 Results and Analysis........................... 178 6.6.1 Beamforming to Find Multipath Arrivals............ 178 6.6.2 Measuring Time Delays with Cross Beam Correlation..... 180 6.6.3 Time Evolution of Cross Beam Measurements......... 183 6.6.4 Range Estimation......................... 187 6.7 Relationship to Waveguide Invariance.................. 189 6.7.1 Computing Striations and β from Cross Beamformer Measure- ments..............................