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Yan's Phd Thesis Sonar Systems for Object Recognition Yan Pailhas Ocean Systems Laboratory, School of EPS Heriot-Watt University A thesis submitted for the degree of Doctor of Philosophy August 2012 c The copyright in this thesis is owned by the author. Any quotation from the thesis or use of any of the information contained in it must acknowledge this thesis as the source of the quotation or information. Abstract The deep sea exploration and exploitation is one of the biggest chal- lenges of the next century. Military, oil & gas, offshore wind farming, underwater mining, oceanography are some of the actors interested in this field. The engineering and technical challenges to perform any tasks underwater are great but the most crucial element in any underwater systems has to be the sensors. In air numerous sensor systems have been developed: optic cameras, laser scanner or radar systems. Unfortunately electro magnetic waves propagate poorly in water, therefore acoustic sensors are a much preferred tool then op- tical ones. This thesis is dedicated to the study of the present and the future of acoustic sensors for detection, identification or survey. We will explore several sonar configurations and designs and their corresponding models for target scattering. We will show that ob- ject echoes can contain essential information concerning its structure and/or composition. i I would like to dedicate this thesis to Simona, la mia bella... ii Acknowledgements And I would like to acknowledge Prof. Yvan Petillot, Dr. Chris Ca- pus, Dr. Keith Brown, Prof. Dave Lane, Prof. Bernie Mulgrew, Len MacLean, Dr. Clement Petres, Dr. Bertrand Lucotte, Dr. P.Y. Mignotte, Dr. Pedro Patron, Dr. Maiwenn Kersaudy Kerhoas, Ist- van Csajaghy, Jamil Sawas, Nicolas Valeyrie, Reg Hollett, Gaetano Canepa, Dr. DJ. Tang, Dr. Ryan Goldhahn, Dr. Hans Groen, Dr. Violetta Sanjuan, Dr. Samantha Dugelay, Dr Duncan Williams and so many others... iii ACADEMIC REGISTRY Research Thesis Submission Name: Yan Pailhas School/PGI: OSL, School of EPS Version: (i.e. First, Final Degree Sought PhD Resubmission, Final) (Award and Subject area) Declaration In accordance with the appropriate regulations I hereby submit my thesis and I declare that: 1) the thesis embodies the results of my own work and has been composed by myself 2) where appropriate, I have made acknowledgement of the work of others and have made reference to work carried out in collaboration with other persons 3) the thesis is the correct version of the thesis for submission and is the same version as any electronic versions submitted*. 4) my thesis for the award referred to, deposited in the Heriot-Watt University Library, should be made available for loan or photocopying and be available via the Institutional Repository, subject to such conditions as the Librarian may require 5) I understand that as a student of the University I am required to abide by the Regulations of the University and to conform to its discipline. * Please note that it is the responsibility of the candidate to ensure that the correct version of the thesis is submitted. Signature of Date: Candidate: Submission Submitted By (name in capitals): Signature of Individual Submitting: Date Submitted: For Completion in the Student Service Centre (SSC) Received in the SSC by (name in capitals): Method of Submission (Handed in to SSC; posted through internal/ external mail): E-thesis Submitted (mandatory for final theses) Signature: Date: iv Contents Contents v List of Figures xi List of Tables xxi Nomenclature xxiv 1 Introduction 1 1.1 Thesis motivations . .1 1.2 Thesis architecture . .2 1.3 Contributions . .5 1.4 Publications . .7 1.4.1 Journal papers . .7 1.4.2 Conferences . .8 2 Sonar Basics 11 2.1 A bit of history . 11 2.2 The transducers . 12 2.2.1 The piezoelectric effect . 13 2.2.2 The piezoelectric components . 14 2.3 Electronics . 15 2.4 The Sonar Equation . 16 2.4.1 Sound speed . 18 2.4.2 The Source Level . 19 2.4.3 The Transmission Loss . 20 v CONTENTS 2.4.4 The Target Strength . 22 2.4.4.1 Spherical target . 23 2.4.4.2 Cylindrical target . 24 2.4.5 The Reverberation Level . 25 2.4.6 The Noise Level . 27 2.4.7 The Beam Pattern and the Directivity Index . 31 2.5 Conclusions . 33 3 Sidescan Sonars 34 3.1 Sidescan systems . 34 3.1.1 Sonar configurations . 34 3.1.2 The sidescan configuration . 36 3.1.3 Sidescan sonar image formation . 37 3.2 Sidescan simulator . 40 3.2.1 Motivations . 40 3.2.2 Simulator . 41 3.2.2.1 3D Digital Terrain Model Generator . 43 3.2.2.2 Targets . 45 3.2.2.3 Sonar Image Generator . 46 3.3 Application: the ATR problem . 50 3.3.1 ATR problem in sonar images . 50 3.3.2 Highlight-based classifier using PCA . 52 3.4 Results . 53 3.4.1 What precision is needed? . 54 3.4.1.1 Identification . 56 3.4.1.2 Classification . 56 3.4.2 Identification with shadow . 59 3.5 Conclusions . 62 4 Synthetic Aperture Sonar 64 4.1 Introduction . 64 4.2 SAS Principles . 65 4.2.1 SAS image formation . 66 vi CONTENTS 4.2.2 Why a low frequency SAS system? . 68 4.3 Synthetic SAS Images of Simple Targets . 69 4.3.1 Scattering theory of concentric spheres . 70 4.3.1.1 Incoming pulse: Spherical wave & plane wave . 70 4.3.1.2 Wave equations . 71 4.3.1.3 Limit conditions . 73 4.3.1.4 Resolution . 75 4.3.1.5 Backscattering echo in the time domain . 76 4.3.2 Synthetic SAS image computation . 77 4.3.3 Comparison between HF-SAS & LF-SAS . 78 4.3.3.1 A world without sound attenuation . 78 4.3.3.2 Sound attenuation . 81 4.3.3.3 LF-SAS vs HF-SAS . 82 4.3.3.4 Discussion and Results . 85 4.4 Reverberation Level in SAS Images . 87 4.4.1 Different theories for seabed scattering behaviour . 87 4.4.2 Small Perturbation Fluid Model . 88 4.4.3 Results . 90 4.4.3.1 Reverberation Level and SNR estimation . 90 4.4.3.2 Comparison between synthetic and real SAS bot- tom echo . 93 4.5 Half-Space Interaction . 96 4.5.1 Resolution of the Helmholtz-Kirchhoff integral . 96 4.5.1.1 Target in the water column . 97 4.5.1.2 Buried target . 97 4.5.2 LF-SAS images of targets with seabed interaction . 98 4.5.2.1 On the seabed case . 99 4.5.2.2 Buried case . 101 4.6 Kirchhoff Model for Target Echoes . 103 4.7 Experiments . 105 4.7.1 Mid water experiments . 106 4.7.2 On the bottom experiments . 107 4.8 On rough interface interactions . 112 vii CONTENTS 4.8.1 About the disagreement between numerical models and ex- perimental results . 112 4.8.2 Models to simulate the bottom interaction . 113 4.8.2.1 Kirchhoff approximation with rough seafloor hy- pothesis . 113 4.8.2.2 Results . 114 4.9 Conclusions . 118 5 Bio-Inspired Sonar 119 5.1 Introduction . 119 5.2 BioSonar . 121 5.2.1 The dolphins' sonar . 121 5.2.1.1 The dolphins' click taxonomy . 121 5.2.1.2 Dolphins' click analysis . 123 5.2.2 BioSonar principles . 125 5.3 Biomimetic pulses . 126 5.4 Broadband echo analysis . 129 5.4.1 Calculation of the Form Function . 129 5.4.2 Theoretical Predictions . 131 5.4.3 Echo structure modelling . 132 5.4.3.1 Echo structure for cylindrical shell with low impedance material . 133 5.4.3.2 Echo structure for cylindrical shell with high impedance material . 134 5.4.4 Numerical simulations . 135 5.4.4.1 Numerical Approach: FDTD Simulator . 136 5.4.4.2 Analogy with geometrical optics . 138 5.4.5 Echo model of man-made objects . 140 5.5 Experiments in controlled environment . 142 5.5.1 Tank experiments . 143 5.5.1.1 Time-Frequency Observations and Echo Timings 143 5.5.1.2 Spectral Matching . 145 viii CONTENTS 5.5.2 Noisy Environment: Small Cylinder Responses in a Harbor Setting . 148 5.6 Classification . 150 5.6.1 Broadband features & classifier . 150 5.6.2 Influence of the noise . 154 5.7 Applications . 154 5.7.1 BioSonar for AUVs . 155 5.7.2 Mine countermeasures . 157 5.7.3 Cable tracking . 164 5.7.3.1 Background . 164 5.7.3.2 Sidescan and BioSonar sensor comparison . 167 5.8 Conclusions . 172 6 MIMO Sonar 173 6.1 Introduction . 173 6.2 Reformulation of the broadband MIMO sonar problem . 174 6.2.1 The RADAR formulation . 174 6.2.2 The random walk analogy . 176 6.2.3 The MIMO sonar extension . 179 6.3 Virtual point scatterers model for a cylindrical shell . 180 6.4 Statistical MIMO . 181 6.4.1 The detection problem with statistical MIMO . 181 6.4.2 Thoughts on the RCS definition and its implications . 185 6.4.3 Super-resolution with MIMO systems ..
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