Fiber-Optic Acoustic Sensors (FOAS) - Northrop Grumman ...

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Legacy Ceramic Array Power In Multiplex and Optical Conversion A/D Conv. Sensor Signal Cond./ Filters ∆V∆P Preamp Hundreds of active electronic and optical components, joints, connectors and interfaces required for each channel Light Weight Wide Aperture Array on Virginia Class Submarines The Navy’s newest Virginia-class submarines employ a Light Weight Wide Aperture Array (LWWAA) on its hull for advanced acoustic detection. The LWWAA system is a set of large array panels that are mounted on either side of the submarine, which provide sonar sensor input to the submarine’s combat system. Instead of traditional ceramic hydrophone sensors, the LWWAA uses FOAS technologies to convert a target submarine’s acoustic energy in the water into information that can be used to identify and track it. Northrop Grumman designed, developed and manufactures the key optical sensing elements of this FOAS array. Towed Arrays Northrop Grumman has designed and developed high channel count fi ber optic towed arrays for submarine applications. The performance of these arrays has been Clock Synchro Acoustic Event ∆P λ0 superior to equivalent ceramic arrays and its ruggedness and reliability have been ex- ceptional. It is expected that future towed array systems will transition to fi ber-optic technology to take advantage of the lower cost, reliability and ruggedness. Surveillance Systems The U.S. Navy and Northrop Grumman continue to be actively involved in the de- velopment of all fi ber-optic acoustic sensor surveillance arrays for anti-submarine war- fare passive sonar. They may be deployed in all types of terrain and marine environ- ments to accommodate such applications as perimeter security, harbor monitoring, and ground surveillance. Depending on the application, these arrays may contain optical geophones, fi ber-optic hydrophones, and/or fi ber-optic microphones. The Centurion Harbor Surveillance program demonstrates our FOAS capabilities in this area. Fiber-Optic Array λ +∆Φ 0 ∆Φ/∆P Optical Interrogation Analog Optical Output Less than 10 passive components and splices per channel Other advantages of fi ber- optic arrays over convention- al arrays include: • Lower power requirements • Increased reliability due to a simplifi ed array design • Reduced maintenance costs • Lower cost to manufacture • No underwater electrical components or wires • Light weight and small cable diameter, which facilitate rapid de- ployment and recovery of the array • Immunity to electromagnetic interference (EMI) • Immunity to high radiation • Diffi cult to detect since the fi ber- optic sensor array is not operated electrically and consists of only non-metallic materials.
�� Centurion Harbor Surveillance Program for Homeland Security Applications Northrop Grumman’s FOAS technology is a key element in the Centurion Port- Harbor Anti-Terrorism/Force Protection system which provides the operator with a complete status of the harbor he is monitoring. This integrated sensor and display product shows the harbor vicinity and potential threats on a standard Navy display system located at the test site. During a demonstration, divers with a battery-powered underwater propulsion device were easily detected attempting to penetrate the harbor. Surface craft traveling in the test area, and entering the restricted Port of Huen- eme, were also detected and tracked. The proof-of-concept demonstration was completed within three months of the contract award by the U.S. Navy’s Mari- time Surveillance Systems Program Offi ce, utilizing passive fi ber-optic sonar arrays and support equipment delivered by Northrop Grumman’s Navigation Systems Division, coupled with commercial-off- the-shelf equipment provided by Northrop Grumman’s Sperry Marine business unit in Charlottesville, Virginia. The equipment provided by Sperry Marine included the marine radar, Automatic Identifi cation System (AIS) shipboard identifi cation system and the digital electronic charting system that provided the com- mon integrated harbor picture. The Northrop Grumman team completed a threat analysis for the port and deter- �� mined the most effective locations to place the underwater arrays. The array installation was performed with the assistance of the Na- val Facilities Engineering Support Center and the team’s ocean engineering subcontractor, Sound and Sea Technology, Inc. of Edmonds, Washington and Ventura, California. Performance benefi ts of this technology include unsurpassed detection, identifi cation and tracking capability for the harbor defense applications. Since no electronic components are in the water, the fi ber-optic arrays provide a highly reliable solution that also offers reduced acquisition and maintenance costs. The arrays employ glass fi bers, instead of older technology piezoelectric hydrophones, to convert sound to modulated light for effi cient transmission to shore.
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