Published on November 6, 2007
Submerged Object Detection with Indirect Passive Sonar: Submerged Object Detection with Indirect Passive Sonar Joseph R. Edwards†, Monica Montanari†, Don L.J. Chiat‡, I.N. Goh‡, Justin A. Nave† and Henrik Schmidt# †VASA Associates, Inc., 8300 Greensboro Dr., Suite 800, McLean, VA 22102 USA ‡Singapore Defence Science and Technology Agency #MIT Department of Mechanical Engineering, Cambridge, MA 02139 USA Outline of Presentation: I. Significance of Port Security in Singapore. II. The Threat Posed by Small Submersibles. III. Vulnerability to Undersea Intrusion. IV. Indirect Passive Sonar (InPaS) for Port Security. V. InPaS Performance Analysis. VI. Role of acoustic propagation modeling. VII. Concluding remarks. Outline of Presentation Economic Consequences of Singapore Port Security: Economic Consequences of Singapore Port Security Malacca & Singapore Straits -> 60000 ships/year this is more than half of the world's merchant fleet capacity. 80% of oil to North Asia passes through the Straits 1/3 of world trade dollars pass through the Straits. If Singapore port/harbor is attacked and closed, impact on world trade is more than $200B (US) per year just counting the impact of disruption to inventory and production cycle. Lloyd’s of London lists the Malacca Straits as a war-risk area … “until such time as they are satisfied that the littoral states were doing more to provide security in the Strait”. In littorals, above-sea surveillance more developed than underwater surveillance. Slide4: USS Cole, Oct. 2000 “Terrorist attack at major US port could cause $1 Trillion damages” -Brookings Institute, 2003 “Navy should conduct a design study for a broad area ocean surveillance system that uses low frequency and broadband acoustics, in concert with fusing data from all-source cooperative vessel tracking systems, to allow for surface vessel location, identification, and tracking and for cueing of sealaunched cruise missile tracking systems.” -Defense Science Board (US) 2003 Study on Roles of DoD in Homeland Security “Mini Submarine-A Vessel of Choice with Drug Cartels and Terrorists” -Vijay Sakhuja , Research Fellow, Observer Research Foundation (India) May 2005 Submersible Threats in the News Slide5: U.S. National Strategy for Maritime Security Needs for Maximizing Domain Awareness: Sensor technology, human intelligence collection, and information processing tools to persistently monitor the maritime domain; Shared situational awareness to disseminate information to users at all levels; Automated tools to improve data fusion, analysis, and management in order to systematically track large quantities of data, and to detect, fuse, and analyze aberrant patterns of activity – consistent with the information privacy and other legal rights of Americans; and In order to advance to the next level of threat detection, transformational research and development programs in information fusion and analysis – these programs will develop the next qualitative level of capability for detection threats. Slide7: Submersible Detection – Active Sonar Benefits: Control of signal band. Direct access to range and azimuth. Matched filter gain. Drawbacks: Two-way transmission loss Large power requirement. Negative impact on marine mammals. Source position and intention visible to all. TL AG TL2 AG TL1 Slide8: Submersible Detection – Passive Sonar Benefits: Minimal power requirement. Minimal impact on marine mammals. Clandestine surveillance. Drawbacks: No range information. Mini-submersibles and divers are very quiet with respect to ambient. No matched filter gain. Acoustic Source Levels: Acoustic Source Levels Arveson averaged ship power spectrum over various operational speeds. Wales averaged ship power spectrum over various types of ships. AUV is SOC Autosub. Ambient noise measured in Singapore Keppel Harbor. Cargo ship source levels are 50 dB greater than submersible source level. 50 dB 70 dB Slide10: Signal Loss from Source-Target + Target Scattering Assumes the target traverses between two ships spaced by 1 km. Target size on the order of 1.5 m diameter. The 30 dB loss value indicates that given sufficient array gain, there is sufficient signal for detection to be made. Sufficient signal level is not the whole story… Relevant Aspects of the Singapore Port Areas: Relevant Aspects of the Singapore Port Areas Heavy ship traffic Many large merchant ships Very shallow water Strong transmission loss Variable sound speed profiles Well-instrumented area Large ship positions well known Bathymetry well mapped 1 km Slide12: Submersible Detection – Indirect Passive Sonar Benefits: Uses cargo ships as sources of opportunity. Relative ranges can be estimated from known ship and receiver positions. Some matched filter gain available. Minimal power requirement – low freq, long range source available. Drawbacks: Possible to have no sources of opportunity (unlikely in busy shipping lanes) Ship signal is correlated to target scattered signal, and in similar arrival angle. Slide13: Δφ Source Target Target Detection Methodology Reception Coherent Portion Incoherent Portion MVDR/MLSE Beamformer Correl./Cepstrum Echo Detector Detection Tracking Tracking Slide14: InPaS Performance – as a function of source-target correlation Correlation coefficient Correlation coefficient Probability of detection Angle estimation error Slide15: InPaS Performance – False Alarm Probability vs. Observation Time As number of snapshots increases, the performance improves for given detection threshold. False alarm probability drops suddenly when detections go to zero. Probability of False Alarm Detection Threshold Increasing # snapshots Detection probability->0 Slide16: broadside source Probability of Detection Angular Estimation InPaS Performance – Determining Sufficient Signal Levels Slide17: InPaS Performance – Determining Sufficient Angular Separation Singapore Keppel Harbor (SKH): Singapore Keppel Harbor (SKH) Green paths are ship traversal paths. Red paths are port entry/exit. Submersible detection must occur in the green zone prior to arrival in red zone. SKH environment gridded as shown below. Slide19: Green zones are preferred receiver locations. Arrays stay outside of direct shipping lanes, near barrier islands. Red gridded area is the source/target area. Target assumed equally likely to be anywhere in the grid. Availability of multiple sources, multiple receive angles. Array Layout for Domain Protection Slide20: Shallow Water Acoustic Propagation – Temporal Variability Slide21: The Synthetic Environment Acoustic Laboratory (SEALAB) Receivers Sources Environment Propagation Model Slide22: Bathymetry Representations in SEALAB U.S. Mid-Atlantic Region Singapore Fairway Slide23: Sonar Simulations in SEALAB Example Sonar Simulation – Singapore Fairway: R Example Sonar Simulation – Singapore Fairway Run parameters Frequency = 1200 Hz Target depth = 11 m DT=AG=0 dB Color scale is -20 dB (blue) to 10 dB (red) Field of view partially blocked by barrier island. Conclusions: Conclusions Undersea access methods to ports of call present a significant security challenge. Unique situation of the Singapore waterways (dense ship traffic, shallow water, well-instrumented area with “Eye in the Sky”) enables cargo ships to be exploited as acoustic sources of opportunity. InPaS can be used in conjunction with additional sensor modalities to detect threats entering the harbor. Pre-deployed fixed arrays can be placed for full area, full-time coverage of a desired waterway.