N121-038 TITLE: Radar Signature Tools for Small Boats in Dynamic Sea Environments

TECHNOLOGY AREAS: Air Platform, Sensors, Battlespace

ACQUISITION PROGRAM: PMA 205

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted". The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: Develop a set of software tools that simulate high-frequency radar signatures for small boats in dynamic littoral and deep water environments.

DESCRIPTION: Small boats at sea cause unique challenges due to their relative size, mobility, and often nonthreatening outward appearance. Detection and identification of potentially threatening small boats in and among other small boats and in proximity to U.S. naval assets is of high interest and importance for the safety of the Fleet. The ability to simulate the radar signatures of small boats in these challenging and dynamic environments aids in developing detection and identification methodologies, algorithms, and systems.

Complicating the problem is the dynamic sea state, which comprises multiple wave phenomena and the dynamic motion of the small boat relative to the sea state, including the position/orientation of the boat and its associated wake as a function of time. Modeling and simulation tools exist for generating a 6-degrees-of-freedom (6-DOF) ship state as a function of time given a sea state and the mass distribution and hull shape of the ship, but these tools typically are not coupled to radar signature modeling and simulation tools. Conversely, a number of high-frequency radar simulation codes are capable of generating radar signatures for objects like small boats, but these typically are not coupled to dynamic models for generating the changing sea state and ship position/orientation as a function of time. Many of these codes also are not suitable for computing the complex scattering mechanisms resulting from the sea state�including gravitational waves, capillary waves, and wake phenomena�and the interaction of this changing sea state with the small boat. Further, the large physical scale of the wake relative to the small boat presents computational problems for both full-wave and high-frequency codes that require a mesh of the entire scene at each time step, which may span hundreds of thousands of wavelengths or more in size and thousands of coherent processing intervals (CPI) in time.

Understanding and exploiting radar signature characteristics of small maritime threats is a key component of maritime surveillance missions. A set of robust tools is required that can accurately model and efficiently predict high-frequency radar signatures for small boat(s) in the changing sea environment over many CPIs. The tools should use high-fidelity physics-based modeling to (1) account for interactions involving motion of the boat and the nearby sea state, (2) include the return of waves and the ship wake, and (3) predict radar returns for one or many CPIs to allow computation of coherent radar cross-section (RCS), synthetic aperture (SAR), and/or inverse SAR (ISAR) images. Approaches should also address how to interface between new or existing sea state modeling tool(s) and how to represent the sea state geometry as a function of time for use in the signature simulation tool.

PHASE I: Develop and demonstrate proof-of-concept prototype algorithms or tools for computing the combined radar return from small boats in a dynamic sea state environment over many seconds of simulated time. Develop a detailed implementation plan including the tool requirements and a graphical user interface (GUI) development to be carried out in Phase II.

PHASE II: Further develop the methods proposed in Phase I and address the computational challenges identified. Develop a GUI to visualize modeling inputs and signature outputs. Integrate the software tools for sea-state generation and signature computation. Demonstrate signature computations for small boats, wakes, and wave phenomena through use cases and tutorials. Demonstrate accuracy and robustness of the computational electromagnetics model for selected evaluation scenarios.

PHASE III: Develop a commercial-grade software tool that solves the end-to-end modeling and simulation problem, including development of necessary interfaces to existing government or commercial software tools for modeling the dynamic sea state and ship motion, as well as a robust GUI and user documentation.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: There are numerous commercial/dual-use applications for this capability, including port security, commercial shipping safety and security, and civilian watercraft protection.

REFERENCES:
1. Pierson, W. J., & Moscowitz, L. (1964). A proposed spectral form for fully developed wind seas based on the similarity theory of S A Kitaigorodskii. Journal of Geophysical Research, 69(24), 5181�5190.

2. Wu, C. H., Young, C. C., Chen, Q. J., & Lynett, P. J. (2010). Efficient non-hydrostatic modeling of nonlinear waves from shallow to deep waters. Journal of Waterway, Port, Coastal, and Ocean Engineering, 136(2), 104-118.

3. Newman, J. N. (1977). Marine hydrodynamics. Cambridge, MA: MIT Press.

4. SAIC. (n.d.). Xpatch Electromagnetic Simulation Software [Computer software]. McLean, VA: Author. Available at http://www.saic.com/products/software/xpatch/

5. Skolnik, M. (1990). Radar handbook (2nd ed.). Columbus, OH: McGraw-Hill.

KEYWORDS: Radar Signatures; Small Craft; Hydrodynamics; Electromagnetic Modeling; Sea Scattering; simulation

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