N092-137 TITLE: Optical Array Shape Estimation (ASE)

TECHNOLOGY AREAS: Ground/Sea Vehicles, Sensors, Electronics

ACQUISITION PROGRAM: TB-29 and TB-33 Towed Array Programs

OBJECTIVE: Develop an innovative optical based towed array shape estimation (ASE) system

DESCRIPTION: Current optical systems can precisely sense the location of surgical instruments and are routinely used to assist surgeons. These and other similar optical sensing technologies have been proposed as potential solutions for realtime awareness of a towed array�s shape. However, there are several significant differences. The towed array application must operate on cable lengths that are two orders of magnitude (thousands of feet vice tens of feet) greater than the medical application. In addition most operational towed arrays are comprised of several interconnected modules and the shape sensing system must pass signals through inter-module couplings/connectors whereas medical systems with much shorter lengths do not have connectors in-line with the sensing system. Current optical ASE technology does not work in Navy towed arrays.

The U.S. Navy currently deploys towed arrays that employ conventional telemetry systems and is developing optical towed array technology to reduce costs, increase reliability, and improve performance. The focus of this SBIR topic is to research and develop innovative solutions to the shortfalls associated with current optical array shape estimation technology and to research and develop algorithms which accept noisy measurements from the optical sensing system. These will then be inputted into a physics based model which computes an accurate real-time estimate of the full three dimensional shape of a towed array. Proposed solutions should be applicable to arrays with conventional, or optical, sensors and telemetry.

Innovative research and development solutions to the following technical issues are sought. The system needs to operate over lengths up to 3,500 feet including tow cable and acoustic array. For this research purposes, assume the 3,500 feet length is 1500 feet of tow cable and 2000 feet of acoustic array. The acoustic array is typically comprised of multiple modules that are interconnected to form the desired aperture. The proposed system needs to operate across module interfaces and therefore be capable of passing the required optical signal(s) from module to module via optical connectors. The number of fibers required to implement the system needs to be minimized in order to reduce the number of optical connectors required from array module to module. Current optical shape sensing signal processing algorithms do not include a physics based model of array tow dynamics and degrade rapidly as the measurement data becomes noisy. A physics based model will need to be developed and integrated into the array shape estimation algorithm to minimize performance degradation as the measurements form the optical sensing system become noisy. The optical shape system needs to provide a full 3-dimensional estimate of the shape of the towed array and needs to be capable of accurately measuring the location and angular rotation of any point along the array axis to within 15 cm and one degree, respectively.

PHASE I: Conduct an analysis to assess the feasibility of using optically sensing technology for a towed array application and the remaining research and development required in the Phase I option and Phase II to implement the proposed solution. The proposed solution(s) should clearly identify how the analysis and study address the current Navy towed array issues related to the full 3-dimensional estimate of shape of towed arrays.

PHASE II: Implement innovation solution(s) based on Phase 1 feasibility analysis of an optical shape sensing technology. Demonstrate the solutions via bench top test and evaluation. Refine system based on bench top test results and finalize the system for in water test.

PHASE III: Integrate the enhanced optical shape sensing technology developed in Phase 2 into a towed array for lake and/or at-sea testing onboard a Research Vessel (R/V). Successful completion of this waterborne testing will enable the optical shape sensing technology into the Navy�s towed arrays.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: This all-optical approach to estimating the shape of a long flexible cable system has applications in tracking the location of tethered vehicles, fixed deployable arrays, and the seismic oil exploration industry. Additionally this all-optical approach to position measurement would have applicability to any problem where knowledge of the shape or location of a long flexible cable is important.

REFERENCES:
1. R. Dominijanni, A method of Estimating Towed Array Shape from Sensor Data, Journal of Underwater Acoustics Vol. 43, No. 4, October 1993, Part I.

2. Special Issue on Sonar System Technology, IEEE Journal of Oceanic Engineering, 18, 543-590 (1993).

3. M. Hinich, Bearing Estimation Using a Perturbed Linear array, Journal Acoustic Society of America, 61, 1540-1544 (1977).

4. H. P. Buckner, Beamforming a Towed Line Array of Unknown Shape, Journal Acoustic Society of America, 63, 1451-1454 (1978).

KEYWORDS: optics, array shape estimation, towed arrays, accuracy, angular rotation

** TOPIC AUTHOR (TPOC) **

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