Fiber Optic Measurement of Towed Array Shape

Sponsored by: Office of Naval Research
Team Member: University of Maryland, College Park

Towed sonar arrays consist of a string of long, flexible modules containing hydrophones that are used to locate underwater noise sources. The location of the sonar modules plays a significant role in being able to accurately identify and locate the source of underwater acoustic noise. Currently, electronic sensors (heading and depth) are used to provide very rough estimates of sonar sensor locations for these applications. A more accurate method of determining the shape of the array has been developed using fiber Bragg grating (FBG) strain sensors. The problem of determining dynamic shape of long, flexible bodies extends to other applications including cables, oil risers, aircraft wings, and the offshore drilling industry.

AITHER has developed a robust method to embed the fiber Bragg grating sensor arrays into the polyurethane hose structure of the towed sonar systems. An in-house strain-to-shape algorithm was developed that takes the embedded strain readings and determines the shape of the array along its entire length. A LabVIEW-based program, the Towed Array Shape Interrogation Tool (TASIT), was then developed to implement the algorithm using real-time FBG wavelength data from Micron Optics, Inc.’s si425 to display the towed sonar array shape in real-time, allowing for varying viewing angles and data control options. This program has been expanded to apply the shape-sensing technology to steel tow cables. Currently, FBG sensors are being integrated into a 2000-foot tow cable for a lake test scheduled for January 2005.