N151-034 TITLE: Active Signal Processing Enhancements for Classification of Low Signal-to-Noise Ratio (SNR) Sonar Signals in Doppler Clutter

TECHNOLOGY AREAS: Sensors, Electronics, Battlespace

ACQUISITION PROGRAM: PEO IWS 5.0, Undersea Warfare Systems

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with section 5.4.c.(8) of the solicitation. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop innovative signal processing algorithms for Doppler sensitive waveform processing that improve detection and classification.

DESCRIPTION: The Navy is seeking to develop signal and information processing for improved performance of Doppler processing in the presence of stationary clutter, ownship induced clutter, and active interference. Innovative signal and information processing algorithms are sought to improve overall performance for Continuous Wave (CW) pulsed waveform processing. Of particular interest are low Signal-to-Noise Ratio (SNR) signals near the clutter ridge. These approaches should seek to improve the probability of detection and classification, while decreasing false alert rate and operator workload. Approaches might include signal processing techniques such as beamforming or statistical signal processing [ref 3], mismatch filtering approaches [ref 4], and others. Information processing improvements may include feature extraction and processing, multi-target tracking, and operator tools and displays.

Mid-frequency pulsed active sonar (MF PAS) systems exploit the Doppler sensitivity of certain waveforms (for example narrowband CW pulses) to aid in detection and classification of submarine and torpedo targets. Spectrogram processing of beam time series data of CW pulses isolates stationary clutter (such as bottom clutter and volume reverberation) to frequency bins near zero Doppler offset. This results in the familiar zero Doppler clutter ridge. In theory, signal echoes with sufficient Doppler can be detected and classified with high confidence provided there is adequate frequency separation from the clutter ridge. In practice, the range-Doppler surface is cluttered by much more than stationary clutter. Own-ship motion leads to a spectral spreading of bottom reverberation, resulting in "shoulders" of elevated noise surrounding the clutter ridge [refs 1, 2]. This suppresses or masks weak contacts even when there is separation from the clutter ridge. Active interference from nearby transmitters appears as discrete broadband impulses in the processing band of interest. These and other sources of spectral splatter adversely affect detection, tracking, and classification capabilities. Adaptive beamformers have been used to reject interference and narrow the frequency extent of the clutter ridge, but are still subject to degraded performance in regions dominated by own-ship motion induced reverberation.

PHASE I: The company will develop signal and information processing concepts for improved performance of Doppler processing in the presence of stationary clutter, own-ship induced clutter, and active interference. The company will demonstrate the feasibility of the concepts in meeting Navy needs and show the feasibility of developing the concepts into useful products for the Navy. Analytical modeling and simulation may be used to demonstrate feasibility. Based on the results of the analysis, the company will determine which concept best meets Navy needs.

PHASE II: Based on the results of Phase I and the Phase II contract statement of work, the small business will develop prototype signal and information processes for evaluation as needed. The prototype will be evaluated to determine its capability in meeting Navy requirements for Mid-frequency active clutter reduction using selected government furnished information (GFI) data sets. Sensor performance will be demonstrated through comparison of results from the prototype methods to current system methods over the required range of parameters. Evaluation results will be used to refine the prototype into a design that will meet Navy requirements. The company will prepare a Phase III development plan to transition the technology to Navy use. It is likely that the Phase II work will require access to classified data.

PHASE III: If Phase II is successful, the company will be expected to provide support to the Navy in transitioning the technology for Navy use. The company will develop real-time computer code that implements the signal and information processing methods and associated computer integration code for evaluation to determine its effectiveness in an operationally relevant environment. The company will assist in integrating and testing the software in a real-time environment, or other advanced processor build program specified by the US Navy. The company will support the Navy in test and validation to certify and qualify the system for Navy use.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Techniques to enhance detection and classification performance in reverberation dominated regions can provide improvement for many commercial applications of active sonar. Bathymetry mapping, fish finding, oil exploration, commercial salvage and rescue/recovery efforts all use active sonar in regions/environments subject to reverberation and interference.

REFERENCES:
1. Cox, H., "Space-time processing for suppression of bottom reverberation," Signals, Systems and Computers, 1995. 1995 Conference Record of the Twenty-Ninth Asilomar Conference on, vol.2, pp.1296,1299 vol.2, Oct. 30 1995-Nov. 1 1995.

2. R. Urick, Principles of Underwater Sound, 3rd Edition. Los Altos Hills, CA: Peninsula Publishing, 1983.

3. D. Manolakis, V. Ingle, and S. Kogon, Statistical and Adaptive Signal Processing. Norwood, MA: Artech House, Inc, 2005.

4. Kesler, S.B.; Haykin, S., "Mismatched Filtering of Sonar Signals," Aerospace and Electronic Systems, IEEE Transactions on the equipment, procedures, and techniques applicable to the organization, installation, and operation of functional systems designed to meet the high performance requirements of earth and space systems. vol.AES-17, no.5, pp.730,734, Sept. 1981.

KEYWORDS: Active sonar; underwater acoustics; clutter reduction in SNR signals; sonar signal processing; low doppler detection; signal processing techniques for sonar

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