Calhoun: The NPS Institutional Archive Theses and Dissertations Thesis Collection 2015-09 Long-endurance maritime surveillance with ocean glider networks Nott, Bradley J. Monterey, California: Naval Postgraduate School http://hdl.handle.net/10945/47308 NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA THESIS LONG-ENDURANCE MARITIME SURVEILLANCE WITH OCEAN GLIDER NETWORKS by Bradley J. Nott September 2015 Thesis Advisor: John E. Joseph Second Reader: Tetyana Margolina 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 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED September 2015 Master’s thesis 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS LONG-ENDURANCE MARITIME SURVEILLANCE WITH OCEAN GLIDER NETWORKS 6. AUTHOR(S) Nott, Bradley J. 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING Naval Postgraduate School ORGANIZATION REPORT Monterey, CA 93943–5000 NUMBER 9. SPONSORING /MONITORING AGENCY NAME(S) AND 10. SPONSORING / ADDRESS(ES) MONITORING AGENCY N/A REPORT NUMBER 11. SUPPLEMENTARY NOTES The views expressed in this thesis are those of the author and do not reflect the official policy or position of the Department of Defense or the U.S. Government. IRB Protocol number ____N/A____. 12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Approved for public release; distribution is unlimited A 13. ABSTRACT (maximum 200 words) This study examines the integration of ocean glider Unmanned Surface Vehicles (USVs) and Unmanned Undersea Vehicles (UUVs) in support of wide-area oceanographic and acoustic sampling. These collaborative systems could enable the U.S. Navy to conduct multi-month unmanned maritime surveillance. Optimal sensor position in the water column and persistence are critical requirements to reduce surface expressions of such a network. An experiment was conducted in Monterey Bay to evaluate underwater gliders as mobile passive acoustic sensing platforms. Acoustic propagation modeling was used to plan experiment geometry, predict transmission loss (TL), and estimate acoustic communications performance with a USV. A medium frequency acoustic source was deployed at a range of 5.5 km from a receiver on board a glider conducting a 1000 m dive to demonstrate that a glider can adapt to the local environment to exploit more reliable propagation paths. Results demonstrate that gliders are effective mobile platforms to support persistent acoustic sensing. The glider received transmitted signals at levels in close agreement with TL predictions. Signals were received while the glider was in motion, and reception improved during a quiet deep loiter. Given the depths, ranges, and environmental conditions studied, research and modeling suggest sufficient acoustic communication performance to promote connectivity of the proposed network. 14. SUBJECT TERMS 15. NUMBER OF Acoustics, Ocean gliders, long-endurance, maritime surveillance, unmanned systems, PAGES oceanographic sampling, passive acoustics, acoustic communications 87 16. PRICE CODE 17. SECURITY 18. SECURITY 19. SECURITY 20. LIMITATION CLASSIFICATION OF CLASSIFICATION OF THIS CLASSIFICATION OF ABSTRACT REPORT PAGE OF ABSTRACT Unclassified Unclassified Unclassified UU NSN 7540–01–280–5500 Standard Form 298 (Rev. 2–89) Prescribed by ANSI Std. 239–18 i THIS PAGE INTENTIONALLY LEFT BLANK ii Approved for public release; distribution is unlimited LONG-ENDURANCE MARITIME SURVEILLANCE WITH OCEAN GLIDER NETWORKS Bradley J. Nott Lieutenant, United States Navy B. A., University of California, Los Angeles, 2006 Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN PHYSICAL OCEANOGRAPHY from the NAVAL POSTGRADUATE SCHOOL September 2015 Approved by: John E. Joseph Thesis Advisor Tetyana Margolina Second Reader Peter Chu Chair, Department of Oceanography iii THIS PAGE INTENTIONALLY LEFT BLANK iv ABSTRACT This study examines the integration of ocean glider Unmanned Surface Vehicles (USVs) and Unmanned Undersea Vehicles (UUVs) in support of wide-area oceanographic and acoustic sampling. These collaborative systems could enable the U.S. Navy to conduct multi-month unmanned maritime surveillance. Optimal sensor position in the water column and persistence are critical requirements to reduce surface expressions of such a network. An experiment was conducted in Monterey Bay to evaluate underwater gliders as mobile passive acoustic sensing platforms. Acoustic propagation modeling was used to plan experiment geometry, predict transmission loss (TL), and estimate acoustic communications performance with a USV. A medium frequency acoustic source was deployed at a range of 5.5 km from a receiver on board a glider conducting a 1000 m dive to demonstrate that a glider can adapt to the local environment to exploit more reliable propagation paths. Results demonstrate that gliders are effective mobile platforms to support persistent acoustic sensing. The glider received transmitted signals at levels in close agreement with TL predictions. Signals were received while the glider was in motion, and reception improved during a quiet deep loiter. Given the depths, ranges, and environmental conditions studied, research and modeling suggest sufficient acoustic communication performance to promote connectivity of the proposed network. v THIS PAGE INTENTIONALLY LEFT BLANK vi TABLE OF CONTENTS I. INTRODUCTION..................................................................................................1 II. BACKGROUND ....................................................................................................3 A. MOTIVATION FOR GLIDER USE .......................................................3 B. N2/N6 PROPOSED STUDY .....................................................................5 C. CONCEPT OF OPERATIONS ................................................................6 1. OPTIMAL SENSOR PLACEMENT ...........................................6 2. LONG-ENDURANCE LOITERING ...........................................8 III. OCEAN ACOUSTICS .........................................................................................11 A. RAY THEORY.........................................................................................11 B. MODIFIED RAY TRACING .................................................................15 C. THE PASSIVE SONAR EQUATION ...................................................16 IV. ACOUSTIC SENSING EXPERIMENT ............................................................19 A. THE BELLHOP ACOUSTIC PROPAGATION MODEL..................19 1. Model Inputs.................................................................................20 a. Sound Speed Profile ..........................................................20 b. Ocean Surface and Bottom Boundaries ...........................22 2. Assumptions and Limitations .....................................................23 B. EXPERIMENT GEOMETRY ................................................................23 C. DATA COLLECTION ............................................................................25 1. Source ............................................................................................26 2. Receiver .........................................................................................27 D. DATA PROCESSING .............................................................................28 1. Ambient Noise Filtering ..............................................................31 2. Self-Noise Considerations ............................................................34 3. Source-to-receiver Range Estimation ........................................34 V. RESULTS .............................................................................................................37 A. TRANSMISSION LOSS COMPARISON .............................................38 B. LOITER ACOUSTICS ............................................................................39 C. LOITER STABILITY .............................................................................41 VI. UNDERWATER ACOUSTIC COMMUNICATIONS ....................................43 A. ACOUSTIC DATA TRANSMISSION ..................................................44 B. NETWORK THROUGHPUT ................................................................44 vii 1. Path and Distance ........................................................................45 2. Signal intensity .............................................................................45 3. Minimizing error ..........................................................................46 C. CHANNEL IMPULSE RESPONSE ......................................................47 D. EXPERIMENTAL RESULTS ................................................................48 E. POWER