Adaptive motion compensation in sonar array processing Adaptive motion compensation in sonar array processing Proefschrift ter verkrijging van de graad van doctor aan de Technische Universiteit Delft, op gezag van de Rector Magnificus prof.dr.ir. J.T. Fokkema, voorzitter van het College voor Promoties, in het openbaar te verdedigen op vrijdag 2 juni 2006 om 10:00 uur, door Johannes GROEN wiskundig ingenieur geboren te Den Haag Dit proefschrift is goedgekeurd door de promotoren: Prof. dr. ir. A. Gisolf Prof. dr. D.G. Simons Samenstelling promotiecommissie: Rector Magnificus, voorzitter Prof. dr. ir. A. Gisolf, Technische Universiteit Delft, promotor Prof. dr. D.G. Simons, Technische Universiteit Delft, promotor Prof. ir. P. van Genderen Technische Universiteit Delft Prof. dr. M.E. Zakharia Ecole Navale, Brest, Frankrijk Prof. dr. A. Stepnowski Gdansk University of Technology, Polen Dr. ir. G. Blacquière, Nederlandse organisatie voor Toegepast Natuurwetenschappelijk Onderzoek Dr. S.P. Beerens, Nederlandse organisatie voor Toegepast Natuurwetenschappelijk Onderzoek Published and distributed by: Netherlands organization for applied scientific research (TNO) P.O. Box 96864 2509 JG The Hague The Netherlands Telephone: +31 70 374 00 00 Telefax: +31 70 374 06 54 E-mail: [email protected] ISBN-10: 90-5986-187-6 ISBN-13: 978-90-5986-187-6 Copyright 2006 by J. Groen All rights reserved. No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the author: J. Groen, TNO, P.O. Box 96864, 2509 JG, The Hague, The Netherlands. Printed in The Netherlands 5 Contents 1. Introduction.......................................................................................................................9 1.1. Background ...............................................................................................................10 1.2. Objective...................................................................................................................11 1.3. Anti Submarine Warfare...........................................................................................11 1.4. Mine hunting.............................................................................................................13 1.5. Requirements analysis ..............................................................................................15 1.5.1. Subdivision in four topics .................................................................................15 1.5.2. Problems and approach.....................................................................................18 1.5.3. Research visualization ......................................................................................18 1.6. Outline.......................................................................................................................19 2. Simulation of sonar data and images ............................................................................21 2.1. Introduction...............................................................................................................21 2.1.1. Basic physics for the simulator suite ................................................................21 2.1.2. Simulator structure............................................................................................25 2.1.3. Primary assumptions in the model....................................................................25 2.1.4. Sonar background knowledge and definitions..................................................25 2.1.5. Outline...............................................................................................................29 2.2. Application of the simulator .....................................................................................29 2.2.1. Application to mine hunting sonar....................................................................30 2.2.2. Application to Anti-Submarine Warfare (ASW) sonars...................................31 2.3. Structure of the simulator..........................................................................................33 2.4. Modular methodology with a collection of models..................................................34 2.4.1. Acoustic response of arbitrary targets...............................................................34 2.4.2. Reverberation....................................................................................................43 2.4.3. Target shadow...................................................................................................48 2.4.4. Multi-path .........................................................................................................49 2.5. Complete simulation for mine hunting .....................................................................52 2.6. Measured synthetic aperture sonar data....................................................................54 2.6.1. Use for signal processing development ............................................................55 2.6.2. Potential for classification.................................................................................59 2.7. Specific features for the Anti-Submarine Warfare towed array sonars ....................59 2.8. Summary and conclusion..........................................................................................62 6 3. Adaptive port/starboard beamforming of triplet sonar arrays..................................63 3.1. Introduction...............................................................................................................63 3.2. Triplet beamformers..................................................................................................66 3.2.1. Optimum triplet beamformer ............................................................................70 3.2.2. Cardioid beamformer........................................................................................71 3.2.3. Adaptive triplet beamformer.............................................................................73 3.3. Theoretical performance ...........................................................................................76 3.4. Sea trial results in noise ............................................................................................80 3.4.1. Experiment set-up .............................................................................................80 3.4.2. Processing chain................................................................................................81 3.4.3. Experiment results ............................................................................................82 3.4.4. Discussion.........................................................................................................84 3.5. Sea trial results in reverberation ...............................................................................84 3.6. Conclusion ................................................................................................................89 4. Doppler corrected array processing..............................................................................91 4.1. Introduction...............................................................................................................91 4.1.1. Background .......................................................................................................91 4.1.2. Operational aspects...........................................................................................93 4.1.3. Outline...............................................................................................................94 4.2. Theoretical performance in a turn.............................................................................94 4.2.1. Error sources.....................................................................................................95 4.2.2. Shape deviations ...............................................................................................95 4.2.3. Doppler shift .....................................................................................................98 4.2.4. Doppler spreading...........................................................................................101 4.3. Compensation methods...........................................................................................103 4.3.1. Signal processing chain...................................................................................103 4.3.2. Method 1: Shape corrected beamforming.......................................................105 4.3.3. Method 2: Stabilized beamforming and dynamic matched filtering ..............106 4.3.4. Method 3: Shape and Doppler corrected beamforming (SDCB)....................107 4.4. Required sonar track accuracy................................................................................108 4.5. Proof of concept on simulations .............................................................................110 4.6. North Sea experiments in 2002...............................................................................111 4.6.1. Experiment description...................................................................................112 4.6.2. Environmental conditions ...............................................................................112 4.6.3. Signal processing