Extremely Low Frequency (ELF) for Anti-Submarine Warfare (ASW)
Navy SBIR 2007.2 - Topic N07-120
NAVAIR - Mrs. Janet McGovern - janet.mcgovern@navy.mil
Opens: May 14, 2007 - Closes: June 13, 2007

N07-120 TITLE: Extremely Low Frequency (ELF) for Anti-Submarine Warfare (ASW)



The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 3.5.b.(7) of the solicitation.

OBJECTIVE: Provide innovative concepts leading to the development of an inexpensive A-size (*) sonobuoy that is capable of detecting and processing Extremely Low Frequency (ELF) magnetic field signals in both deep and shallow water regions.

DESCRIPTION: A sonobuoy that could detect the ELF (0.5 to 30 Hz.) emissions from a submarine would be an appealing complement to the U.S. Navyís acoustic detection capability. This concept is unique in that it is the first time that an effort has been made to provide this magnetic capability in a free floating sonobuoy. These emissions arise from the modulation of the corrosion currents of the submarine, and they are expected to be of substantial value in poorly maintained platforms. This band of frequencies is of interest because at these higher magnetic detection frequencies, the usual electromagnetic noise sources (geology, geomagnetic, motion and wave) should be much less of an issue than in the traditional magnetic anomaly detection (MAD) frequency band. The sensor should be able to detect ELF signals independently, and the cost should be within the cost envelope of the expendable acoustic sensors in use today. The sensor/processing package must be compatible with that of an A-sized sonobuoy and employ the same data link. A major challenge in this effort will be the ocean engineering. Innovative design concepts are sought to develop a free-floating magnetic sensor that provides isolation from ocean induced motion noise. Other technical challenges include the choice of sensing element, sensor orientation, electrical power and size.

PHASE I: Determine the feasibility of developing an optimal magnetic field sensor for this application. Categorize and quantify the various noise sources that the free-floating magnetic field sensor will experience. Conduct operational analyses to predict the performance of these sensors against various target strength levels in the presence of the various noises.

PHASE II: Develop the critical technologies identified in Phase I. Fabricate, test, and evaluate an over the side stand-alone prototype of the system. Demonstrate that the prototype system meets performance requirements in a laboratory environment.

PHASE III: Optimize the system design based upon the test and evaluation results of Phase II. Fabricate A-size prototype units and conduct at-sea tests with operational commands. Integrate the system into the air platformís missions and ensure compatibility with avionics and platforms.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Variants of the system could be used in oil, gas, and mineral exploration fields to measure magnetic signals that characterize these fields taking into consideration the various geomagnetic and geologic background noises.

REFERENCES: 1) M. B. Kraichman, "Handbook of Electromagnetic Propagation in Conducting Media," Second Printing, U.S. Government Printing Office, Stock No. 008-040-00074-5 (1976).
2) E. C. Field, "High-Latitude Geomagnetic and Atmospheric Noise in the 0.001 to 100Hz Frequency Band," Pacific Sierra Research Report No. 2158 (1991).
3) R. J. Dinger and J. A. Goldstein, "Spatial Coherence Measurements and Evaluation of a Noise Reduction Technique for Ambient Noise from 0.3 to 40Hz," NRL report No. 8430 (October 1980).
4) K. A. Poehls, M. J. Shearer, R. F. Sinclair, D. M. Crandall, and C. I. McNeil, "ELF Noise and Signal Detection," Pacific Sierra Research Corporation, Report No. 2544 (March 1995).

(*) A-size refers to the standard U.S. Navy Sonobouy form factor. A-size dimensions are 4.875" D x 36" L

KEYWORDS: ELF Signals; Geomagnetic Noise; Geologic Noise; Shallow Water; ASW; Underwater Sensors

TPOC: (301)342-2535
2nd TPOC: (301)342-2048

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