DOCSLIB.ORG

Interferometric Synthetic Aperture Sonar Design and Performance

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Interferometric Synthetic Aperture Sonar Design and Performance Interferometric Synthetic Aperture Sonar Design and Performance Philip J. Barclay, B.E. (Hons) A thesis presented for the degree of Doctor of Philosophy in Electrical and Computer Engineering at the University of Canterbury, Christchurch, New Zealand. August 2006 ABSTRACT Synthetic aperture sonar (SAS) has become a well developed imaging technique for imaging shallow water environments. Aperture synthesis provides high along-track res- olution imagery, with range independent resolution. However, mapping of the seafloor using traditional SAS is limited to a two-dimensional surface. To provide the third dimension (height), an interferometric synthetic aperture sonar (InSAS) is formed, comprising of two or more vertically displaced hydrophone arrays. Each of the inter- ferometric receiver datasets are processed using standard SAS algorithms, with motion compensation and corrective processing applied equally to each channel, preserving the underlying interferometric time delays. By then estimating the time delay of the incoming wavefronts across the interferometric receiver array, the height of the seafloor can be inferred from the side-scan geometry of the system. The InSAS approach is sim- ilar to the radar equivalent (InSAR), however, significant differences in geometry and medium properties limit the applicability of InSAR algorithms to the sonar equivalent. A height estimate from interferometric data is formed by estimating the time dif- ference between the receiver elements of the interferometric array. Therefore, for an accurate estimate of the time-delay, the signals of the receivers must contain significant ‘common’ information. Presented in this thesis is an analysis of coherence as applica- ble to an InSAS system. The coherence of an InSAS system can be decomposed into five ‘coherence components’: additive acoustic noise, footprint misalignment, baseline decorrelation, temporal decorrelation, and processing noise. Of these, it is shown foot- print misalignment has the greatest effect for an InSAS system if it is not corrected for. The importance of maintaining high coherence between the receiver channels is presented; small losses in coherence from the ideal of unity will have a significant im- pact of the accuracy of the resulting height estimate. To reduce the sensitivity of the height accuracy losses, multiple estimates of the height can be formed from independent ‘looks’ of the scene. Combining all these estimates into one height estimate is shown to significantly improve the height estimate. The design and signal processing of an InSAS system is of high importance to the generation of high accuracy height estimates of the seafloor. Several parameters of design are explored, in particular the effect of aperture sampling. Low along-track aperture sampling rates are shown to cause a significant decrease in signal coherence, iv ABSTRACT caused by the generating of ‘grating lobes’ from the synthetic aperture processing. Substantial improvements can be made by careful selection of transmitter and receiver element sizes, relaxing the requirements of a highly sampled aperture. An analysis of interpolation schemes on interferometric quality is also presented. The effect of footprint misalignment can be reduced by first resampling the data from each receiver onto a common ground-plane. However, this requires prior knowl- edge of the seafloor height, an unknown parameter before an interferometric height estimate is made. One possible method to form an initial height estimate is through the use of belief propagation, a technique applied from the field of stereo imaging. Be- lief propagation is used to estimate an initial height surface, albeit at discrete height intervals. This initial low resolution height surface can then be used to remap the data, partially eliminating the detrimental effects of footprint misalignment. The combination of all the independent estimates of the scene can be combined us- ing maximum likelihood estimation. This framework allows the individual estimates to be combined into one overall cost function. Searching of the cost function for minimum cost yields a single interferometric time-delay estimate, from which a single height esti- mate can be inferred. This framework allows looks formed from many different sources to be combined, including multiple imaging frequency bands, and the use of more than one interferometric pair of receivers. ACKNOWLEDGEMENTS Thank you to everyone who has helped me throughout this thesis. To my supervisors, Dr. Michael Hayes and Prof. Peter Gough, thank you for your guidance and useful discussions along the way. Thank you to the rest of the Acoustic Research Group, in particular Hayden Callow, Steve Fortune, Alan Hunter, and Edward Pilbrow. Also, thanks to Chris Forne for help with the application of belief propagation algorithms. During my stay as a postgrad in the ECE department I have had much support from the department, both from students and staff. It is these fantastic people that make writing a thesis possible. The construction and operation of the KiwiSAS sonar system was an integral part of the early work conducted in this thesis. Much of the mechanical work for the KiwiSAS system was performed by the technical staff of the ECE Department, in particular thanks goes to Michael Cusdin, Peter Lambert, and Steve Downing. For sea-trials of the KiwiSAS system, the use of Peter’s yacht was of much help, I hope we didn’t scratch it too much dragging things back onboard. To my family, thank you for always believing in me, and being there for me through the hard times. A special thank you to Helen. Your love and support means a lot to me. Thank you also to all my friends, especially those who dragged me away into the hills to get away from it all for a while. PREFACE The work in this thesis originally began as a hardware based extension of the KiwiSAS- II sonar system to allow for interferometric operation. The idea was to re-wire the exist- ing 3×3 array of hydrophone elements into three vertically separated receivers, allowing interferometry to be performed. For this, the acquisition hardware was extended to six channels, allowing each hydrophone to operate within two separate frequency bands, centered on 30 kHz and 100 kHz. The hardware developed for this system is covered in [Barclay et al., 2002a], expanded in Appendix B. Sea-trials with this hardware were performed locally in Lyttelton Harbour [Barclay et al., 2001], and the Hauraki Gulf Auckland [Hayes et al., 2001]. Later, the hardware was completely redesigned and rebuilt since it was apparent additional hydrophones would be of benefit. Instead of sending the received wave- forms up the cable in an analogue form, all the conversion and storage electronics was moved into the towfish housing. This was necessitated by the large increase in overall datarate from the expanded sonar configuration. Central to this electronics package is a Pentium-III industrial computer, mounted within a Compact-PCI cage [Hayes et al., 2002]. Waveform generation and echo recording implemented as three custom Compact-PCI cards. This configuration allows the transmitter to be driven in vertical groups of three, allowing synthetic horizontal beam shaping. The new receiver hardware provides nine channels, allowing the 3 × 3 receiver array to be individually sampled, each with a bandwidth of ≈150 kHz. Post-processing is used to extract the two 20 kHz bandwidth signals. During initial interferometric processing, direct phase differences between the re- ceiver channels were used as the basis of the angle-of-arrival [Barclay et al., 2002b, Bar- clay et al., 2003b]. Direct phase differences between the receivers was found to give poor results; the coherence loss due to footprint shift being the primary problem. This is covered in more detail in Chapter 3. The coherence loss due to footprint shift was exploited by resampling the data onto a range of differing height ground-planes, with a surface mapped through the solution space. The fitting of the surface through the solution space was performed using belief propagation, a technique first developed in the computer graphics field. This technique provides a good first order approximation to the seafloor topography. The details of this application of belief propagation can be viii PREFACE found in [Barclay et al., 2003a], reproduced in Appendix A. After a more in-depth analysis of signal coherence between the receivers was per- formed (see Chapter 3), it became apparent multiple ‘looks’ of the scene would be required to provide a high accuracy height estimate. Through various techniques de- tailed in Chapter 4, multiple looks of the scene could be generated. However, the combination of all the looks into one overall height estimate proved difficult, especially when combining data from the two distinct frequency bands (30 and 100 kHz). To achieve this combination, a maximum likelihood approach was taken. The data from each look is formed such that a single parameter search can be made to find the most likely angle-of-arrival. This approach has shown to be highly successful, results pre- sented in several papers [Barclay et al., 2004, Barclay et al., 2005, Barclay et al., 2006]. One major problem with a maximum likelihood approach is the assumption of a single angle-of-arrival, an assumption violated by multipath from the sea-surface. Work on this problem has also been performed both using belief propagation [Hayes and Barclay, 2003] and maximum likelihood approaches [Barclay et al., 2006]. Papers prepared during this thesis are presented here in order of presentation. Barclay, P. J., Forne, C. J., Hayes, M. P., and Gough, P. T. (2003a). Reconstruct- ing seafloor bathymetry with a multi-frequency, multi-channel broadband InSAS using belief propagation. In Oceans 2003. IEEE, MTS. Barclay, P. J., Hayes, M. P., and Gough, P. T. (2001). Using a multi-frequency synthetic aperture sonar for bathymetry. In Image and Vision Computing New Zealand 2001, pages 63–68, University of Otago, Dunedin, New Zealand. Barclay, P. J., Hayes, M. P., and Gough, P.
Load more

Recommended publications
  • Direction-Of-Arrival Estimation Methods in Interferometric Echo Sounding
    sensors Review Direction-of-Arrival Estimation Methods in Interferometric Echo Sounding Piotr Grall * , Iwona Kochanska and Jacek Marszal Faculty of Electronics, Telecommunications and Informatics, Gdansk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland; [email protected] (I.K.); [email protected] (J.M.) * Correspondence: [email protected] Received: 24 May 2020; Accepted: 20 June 2020; Published: 23 June 2020 Abstract: Nowadays, there are two leading sea sounding technologies: the multibeam echo sounder and the multiphase echo sounder (also known as phase-difference side scan sonar or bathymetric side scan sonar). Both solutions have their advantages and disadvantages, and they can be perceived as complementary to each other. The article reviews the development of interferometric echo sounding array configurations and the various methods applied to determine the direction-of-arrival. “Interferometric echo sounder” is a broad term, applied to various devices that primarily utilize phase difference measurements to estimate the direction-of-arrival. The article focuses on modifications to the interferometric sonar array that have led to the state-of-the-art multiphase echo sounder. The main algorithms for classical and modern interferometric echo sounder direction-of-arrival estimation are also outlined. The accuracy of direction-of-arrival estimation methods is dependent on the configuration of the array and external and internal noise sources. The main sources of errors, which influence the accuracy of the phase difference measurements, are also briefly characterized. The article ends with a review of the current research into improvements in the accuracy of interferometric echo sounding and the application of the principle of interferometric in other devices.
    [Show full text]
  • The Third Battle
    NAVAL WAR COLLEGE NEWPORT PAPERS 16 The Third Battle Innovation in the U.S. Navy's Silent Cold War Struggle with Soviet Submarines N ES AV T A A L T W S A D R E C T I O N L L U E E G H E T R I VI IBU OR A S CT MARI VI Owen R. Cote, Jr. Associate Director, MIT Security Studies Program The Third Battle Innovation in the U.S. Navy’s Silent Cold War Struggle with Soviet Submarines Owen R. Cote, Jr. Associate Director, MIT Security Studies Program NAVAL WAR COLLEGE Newport, Rhode Island Naval War College The Newport Papers are extended research projects that the Newport, Rhode Island Editor, the Dean of Naval Warfare Studies, and the Center for Naval Warfare Studies President of the Naval War College consider of particular Newport Paper Number Sixteen interest to policy makers, scholars, and analysts. Candidates 2003 for publication are considered by an editorial board under the auspices of the Dean of Naval Warfare Studies. President, Naval War College Rear Admiral Rodney P. Rempt, U.S. Navy Published papers are those approved by the Editor of the Press, the Dean of Naval Warfare Studies, and the President Provost, Naval War College Professor James F. Giblin of the Naval War College. Dean of Naval Warfare Studies The views expressed in The Newport Papers are those of the Professor Alberto R. Coll authors and do not necessarily reflect the opinions of the Naval War College or the Department of the Navy. Naval War College Press Editor: Professor Catherine McArdle Kelleher Correspondence concerning The Newport Papers may be Managing Editor: Pelham G.
    [Show full text]
  • State of the Art in Swath Bathymetry Survey Systems
    International Hydrographie Review, Monaco, LXV(2), July 1988 STATE OF THE ART IN SWATH BATHYMETRY SURVEY SYSTEMS by Christian de MOUSTIER (*) Paper originally presented at the symposium on ‘Current Practices and New Technology in Ocean Engineering’ held by the American Society o/ Mechanical Engineers (ASME) in New Orleans, Louisiana, 10-13 January 1988, and reprinted with the hind authorization of the symposium’s organizers. Abstract In the last decade, advances in real-time computing and data storage capabilities have led to significant improvements in bathymetric survey systems and the single point echo-sounder has now been replaced by a variety of high- resolution swath mapping sounding systems. This paper reviews the state of the art in the non-military swath bathymetry mapping systems. Such systems are typically multi narrow beam echo-sounders or interferometric side-looking sonars with swath width capabilities ranging from 0.75 to 7 times the water depth. The paper compares the design characteristics and the echo processing methods used in a number of these systems manufactured in Japan, Finland, Norway, the U.K., the U.S.A. and West Germany. 1. INTRODUCTION The outcome of a bathymetric survey is a map of water depths in a geographic reference frame. In rivers, estuaries, navigational channels, harbors and in shallow coastal waters, concerns for navigational safety underscore the need for such surveys. In tne open ocean, the incentive for bathymetric surveys is mostly of an exploratory nature, although seamounts are potentially hazardous to submarine navigation. Knowledge of seafloor relief helps marine geologists draw inferences on the dynamic processes that shape the Earth.
    [Show full text]
  • Enabling Shallow-Water Sidescan Sonar Surveys: Using
    Enabling Shallow-Water Sidescan Sonar Surveys: Using Across-Track Beamforming on Receive to Suppress Multipath Interference by Stephen K. Pearce M.A.Sc., Simon Fraser University, 2010 B.S., Washington State University, 2006 a Thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the School of Engineering Science Faculty of Applied Sciences c Stephen K. Pearce 2014 SIMON FRASER UNIVERSITY Summer 2014 All rights reserved. However, in accordance with the Copyright Act of Canada, this work may be reproduced without authorization under the conditions for \Fair Dealing." Therefore, limited reproduction of this work for the purposes of private study, research, criticism, review and news reporting is likely to be in accordance with the law, particularly if cited appropriately. APPROVAL Name: Stephen K. Pearce Degree: Doctor of Philosophy Title of Thesis: Enabling Shallow-Water Sidescan Sonar Surveys: Using Across- Track Beamforming on Receive to Suppress Multipath Inter- ference Examining Committee: Dr. Carlo Menon, Associate Professor Chair Dr. John Bird, Professor, Senior Supervisor Dr. Ivan Bajic, Associate Professor, Supervisor Dr. Paul Ho, Professor, Supervisor Dr. Jie Liang, Associate Professor, Internal Examiner Dr. Jonathan Preston, External Examiner, Adjunct Professor School of Earth and Ocean Sciences University of Victoria Date Approved: June 25, 2014 ii Partial Copyright Licence iii Abstract Sidescan sonars are used to provide a high resolution 2D image of the seafloor, but when used in shallow water these side-looking systems are vulnerable to multipath interference. In some cases, this interference affects image interpretation and downstream processing such as target recognition or bottom classification.
    [Show full text]
  • A CTFM Synthetic Aperture Sonar 101 6.1.1 Projector Radiation Pattern 101 6.1.2 Hydrophone Response 103 X
    CT M s THE C u E Michael P. Hayes, B.E. (Hons) A thesis presented for the degree of Doctor of Philosophy in Electrical and Electronic Engineering, at the University of Canterbury, Christchurch, New Zealand. September 1989. ENGINEERING L1~f\AP-Y iii st Thls thesis describes the theory and operation of a seafloor imaging Synthetic Aper­ ture Sonar (SAS), based on broadband Continuous Tone Frequency Modulation (CTFM). Narrowband synthetic aperture techniques are reviewed, and some of the limita­ tions of using such techniques in sonar applications are described. Aperture under­ sampling is a particular problem when towing single-beam sonars at realistic speeds. However, the mapping rate constraints may be relaxed by using broadband signals, but at the expense of increased self-clutter (or background). One such broadband signal that is suitable for synthetic aperture operation is CTFM. The signal processing requirements for the CTFM signal are investigated, and are shown to be considerably simplified by decomposing each echo sweep into an ensemble of narrowband components. Images reconstructed from each of these components may be combined in a variety of ways. The relative merits of these differing methods are examined using a computer simulation of a side-scan CTFM sonar. The temporal phase stability of the acoustic environment is vital to the formation of a synthetic aperture. An experiment was performed whlch indicates that the phase stability is much better than anticipated, and certainly adequate for the formation of undersea synthetic apertures. Thls prediction was confirmed by another experiment in which the prototype CTFM sonar was moved along a fixed cableway under realistic operating conditions.
    [Show full text]
  • Dynamic Towed Array Models and State Estimation for Underwater Target Tracking
    Calhoun: The NPS Institutional Archive Theses and Dissertations Thesis Collection 2013-09 Dynamic towed array models and state estimation for underwater target tracking Stiles, Zachariah H. Monterey, California: Naval Postgraduate School http://hdl.handle.net/10945/37725 NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA THESIS DYNAMIC TOWED ARRAY MODELS AND STATE ESTIMATION FOR UNDERWATER TARGET TRACKING by Zachariah H. Stiles September 2013 Thesis Co-Advisors: Robert G. Hutchins Xiaoping Yun Approved for public release; distribution is unlimited THIS PAGE INTENTIONALLY LEFT BLANK REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188 Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruction, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188) Washington DC 20503. 1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED September 2013 Master’s Thesis 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS DYNAMIC TOWED ARRAY MODELS AND STATE ESTIMATION FOR UNDERWATER TARGET TRACKING N/A 6. AUTHOR(S) Zachariah H. Stiles 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION Naval Postgraduate School REPORT NUMBER Monterey, CA 93943-5000 9. SPONSORING /MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10.
    [Show full text]
  • A Review on Deep Learning-Based Approaches for Automatic Sonar Target Recognition
    electronics Review A Review on Deep Learning-Based Approaches for Automatic Sonar Target Recognition Dhiraj Neupane and Jongwon Seok * Department of Information and Communication Engineering, Changwon National University, Changwon-si, Gyeongsangnam-do 51140, Korea; [email protected] * Correspondence: [email protected] Received: 13 October 2020; Accepted: 19 November 2020; Published: 22 November 2020 Abstract: Underwater acoustics has been implemented mostly in the field of sound navigation and ranging (SONAR) procedures for submarine communication, the examination of maritime assets and environment surveying, target and object recognition, and measurement and study of acoustic sources in the underwater atmosphere. With the rapid development in science and technology, the advancement in sonar systems has increased, resulting in a decrement in underwater casualties. The sonar signal processing and automatic target recognition using sonar signals or imagery is itself a challenging process. Meanwhile, highly advanced data-driven machine-learning and deep learning-based methods are being implemented for acquiring several types of information from underwater sound data. This paper reviews the recent sonar automatic target recognition, tracking, or detection works using deep learning algorithms. A thorough study of the available works is done, and the operating procedure, results, and other necessary details regarding the data acquisition process, the dataset used, and the information regarding hyper-parameters is presented in
    [Show full text]
  • Implementation of Adaptive and Synthetic-Aperture Processing Schemes in Integrated Active–Passive Sonar Systems
    Implementation of Adaptive and Synthetic-Aperture Processing Schemes in Integrated Active–Passive Sonar Systems STERGIOS STERGIOPOULOS, SENIOR MEMBER, IEEE Progress in the implementation of state-of-the-art signal- NOMENCLATURE processing schemes in sonar systems is limited mainly by the moderate advancements made in sonar computing architectures Complex conjugate transpose operator. and the lack of operational evaluation of the advanced processing Power spectral density of signal . schemes. Until recently, matrix-based processing techniques, such as adaptive and synthetic-aperture processing, could not AG Array gain. be efficiently implemented in the current type of sonar systems, Small positive number designed to main- even though it is widely believed that they have advantages that can address the requirements associated with the difficult tain stability in normalized least mean operational problems that next-generation sonars will have to square adaptive algorithm. solve. Interestingly, adaptive and synthetic-aperture techniques Narrow-band beam-power pattern of may be viewed by other disciplines as conventional schemes. For a line array expressed by the sonar technology discipline, however, they are considered as advanced schemes because of the very limited progress that has . been made in their implementation in sonar systems. Broad-band beam-power pattern of a line This paper is intended to address issues of implementation of array steered at direction . advanced processing schemes in sonar systems and also to serve as a brief overview to the principles and applications of advanced Beams for conventional or adaptive sonar signal processing. The main development reported in beam formers or plane wave this paper deals with the definition of a generic beam-forming response of a line array steered structure that allows the implementation of nonconventional at direction and expressed by signal-processing techniques in integrated active–passive sonar .
    [Show full text]
  • Underwater Acoustics
    Monograph Series in UNDERWATER ACOUSTICS Sponsored by Office of Naval Research Editorial Board: Ralph R. Goodman, Ph.D., Chair Homer P. Bucker, Ph.D. Ira Dyer, Ph.D. Jeffrey A. Simmen, Ph.D. Monograph Series in UNDERWATER ACOUSTICS In 2001 the Office of Naval Research began a program to publish a selected mono- graph series in the field of underwater acoustics. The series publishes in-depth reviews and analysis on the state of understanding of the physics of sound in se- lected areas of research. The monograph series covers the most important topics in underwater sound in an in-depth, critical, scholarly, and comprehensive fashion. It is intended to provide researchers with an understanding of the physics of underwater sound, based on both theory and experiment. The discussion of important unanswered questions is encouraged. Topics of particular importance in the field are low-frequency sound in the deep ocean, shallow-water acoustics, and ambient noise. Sponsored by: Office of Naval Research One Liberty Center 875 North Randolph Street, Suite 1425 Arlington, VA 22203-1995 E-mail: [email protected] Series Editors: Ralph R. Goodman, Ph.D. Homer P. Bucker, Ph.D. Research Professor 808 Moana Drive USM Department of Marine Science San Diego, CA 92106 1020 Balch Blvd E-mail: [email protected] Stennis Space Center, MS 39529 E-mail: [email protected] Ira Dyer, Ph.D. Jeffrey A. Simmen, Ph.D. Weber Shaughness Professor Applied Physics Laboratory of Ocean Engineering, Emeritus University of Washington Massachusetts Institute of Technology 1013 NE 40th Street Cambridge, MA 02139 Seattle, WA 98105-6698 E-mail: [email protected] Charles H.
    [Show full text]
  • Signature Redacted- Hesis Supervisor a Ccep Ted by
    Evaluation by Simulation of an Acoustic Array Composed of Multiple Autonomous Vehicles by Kerry Noonan Bosch6 B.S., United States Naval Academy (2005) M.S., Naval Postgraduate School (2006) Submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degrees of ARCHES0 Naval Engineer MASSACHUSETTS INSTITUTE OF TECHNOLOLGY and 0 Master of Science in Mechanical Engineering JUL 3 2015 at the LIBRARIES MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2015 @2015 Kerry Noonan Bosch6, All Rights Reserved. The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known or hereafter created. Author .. Signature redacted.............. Department of Mechanical Engineering -2 May 21, 2015 Certified by......Signature redacted................ Henrik Schmidt Professor Signature redacted- hesis Supervisor A ccep ted by ... .. - - - - - -- - - - ................ David Hardt Chairman, Department Committee on Graduate Students 2 Evaluation by Simulation of an Acoustic Array Composed of Multiple Autonomous Vehicles by Kerry Noonan Bosch6 Submitted to the Department of Mechanical Engineering on May 21, 2015, in partial fulfillment of the requirements for the degrees of Naval Engineer and Master of Science in Mechanical Engineering Abstract Ship-towed arrays have been integral to Navy combatant operations for many decades. The continual advancement of towed array technology has been continually driven by the need for high sensitivity, low self-noise, and response across a wide range of fre- quencies. Robotic autonomy, as applied to acoustic sensors, is currently operationally limited to deployment of traditional arrays from semi-submersible tow vehicles. while such a configuration facilitates flexibility in array placement and a measure of stealth, it is an intermediate step toward fully-submerged, autonomous arrays.
    [Show full text]
  • Compressive Underwater Sonar Imaging with Synthetic Aperture Processing
    remote sensing Article Compressive Underwater Sonar Imaging with Synthetic Aperture Processing Ha-min Choi 1 , Hae-sang Yang 1 and Woo-jae Seong 1,2,* 1 Department of Naval Architecture and Ocean Engineering, Seoul National University, Seoul 08826, Korea; [email protected] (H.-m.C.); [email protected] (H.-s.Y.) 2 Research Institute of Marine Systems Engineering, Seoul National University, Seoul 08826, Korea * Correspondence: [email protected]; Tel.: +82-2-880-7332 Abstract: Synthetic aperture sonar (SAS) is a technique that acquires an underwater image by synthesizing the signal received by the sonar as it moves. By forming a synthetic aperture, the sonar overcomes physical limitations and shows superior resolution when compared with use of a side-scan sonar, which is another technique for obtaining underwater images. Conventional SAS algorithms require a high concentration of sampling in the time and space domains according to Nyquist theory. Because conventional SAS algorithms go through matched filtering, side lobes are generated, resulting in deterioration of imaging performance. To overcome the shortcomings of conventional SAS algorithms, such as the low imaging performance and the requirement for high-level sampling, this paper proposes SAS algorithms applying compressive sensing (CS). SAS imaging algorithms applying CS were formulated for a single sensor and uniform line array and were verified through simulation and experimental data. The simulation showed better resolution than the !-k algorithms, one of the representative conventional SAS algorithms, with minimal performance degradation by side lobes. The experimental data confirmed that the proposed method is superior and robust with respect to sensor loss.
    [Show full text]
  • Signal Processing for Synthetic Aperture Sonar Image Enhancement
    Signal Processing for Synthetic Aperture Sonar Image Enhancement Hayden J. Callow B.E. (Hons I) A thesis presented for the degree of Doctor of Philosophy in Electrical and Electronic Engineering at the University of Canterbury, Christchurch, New Zealand. April 2003 Abstract This thesis contains a description of SAS processing algorithms, offering improvements in Fourier-based reconstruction, motion-compensation, and autofocus. Fourier-based image reconstruction is reviewed and improvements shown as the result of improved system modelling. A number of new algorithms based on the wavenumber algorithm for correcting second order effects are proposed. In addition, a new framework for describing multiple-receiver reconstruction in terms of the bistatic geometry is presented and is a useful aid to understanding. Motion-compensation techniques for allowing Fourier-based reconstruction in wide- beam geometries suffering large-motion errors are discussed. A motion-compensation algorithm exploiting multiple receiver geometries is suggested and shown to provide substantial improvement in image quality. New motion compensation techniques for yaw correction using the wavenumber algorithm are discussed. A common framework for describing phase estimation is presented and techniques from a number of fields are reviewed within this framework. In addition a new proof is provided outlining the relationship between eigenvector-based autofocus phase esti- mation kernels and the phase-closure techniques used astronomical imaging. Micron- avigation techniques are reviewed and extensions to the shear average single-receiver micronavigation technique result in a 3{4 fold performance improvement when operat- ing on high-contrast images. The stripmap phase gradient autofocus (SPGA) algorithm is developed and extends spotlight SAR PGA to the wide-beam, wide-band stripmap geometries common in SAS imaging.
    [Show full text]