OBJECTIVE: Develop a software tool integrating high- and low-frequency techniques to accurately and rapidly predict high-resolution radar signatures of sea targets. DESCRIPTION: At X-band and above, boats and ships at sea present rich radar signatures with high potential as the basis of automated target identification. The development and testing of target identification algorithms depends on the rapid and accurate generation of high-resolution radar signatures under diverse sensor conditions and sea states. Raw radar cross section (RCS) is equally important from the perspective of target detection. At these frequencies, even small boats are electrically large, suggestive of a high-frequency (asymptotic) approach. When the immediately surrounding sea state is considered, the need for a high-frequency approach is magnified. Over a broad range of frequencies, electromagnetic interaction of the boat with a non-uniform sea surface can significantly influence its overall signature. However, boats and ships include smaller structures that may contribute significantly to the overall RCS and feature prominently in high-resolution signatures. Owing to the modest electrical size of these topside features, exclusive reliance on asymptotic methods is insufficient. These component structures are more suitably captured using low-frequency (full-wave) techniques. More generally, the large-scale structure of the ship or boat that is well modeled with a high-frequency method may not be the dominant source of radar return. Even though the broad structures scatter more of the incident radar wave than the detailed features, these structures tend to scatter energy in particular directions far away from the radar sensor. At the same time, there are many detailed structures on the boat topside that, by virtue of both their smaller electrical size and geometric complexity, scatter significantly over a broader range of angles, including the backscattering direction. Complicating the situation further, the returns from these detailed features are often significantly influenced through interaction with the large-scale surfaces of the boat. Even though the direct return from these large surfaces may be weak, their indirect return mediated by topside features can be significant. Ideally, the entire problem would be solved with full-wave methods, which are intrinsically more accurate than asymptotic approximations. However, even with modern algorithmic and hardware accelerations, this is not feasible in the foreseeable future. Given the mixed scale of the problem at X-band and above, what is needed is a combined asymptotic/full-wave (hybrid) technique that exploits the respective strengths of such methods to solve the overall problem. Further, given the electromagnetic interaction between these mixed-scale features, it is important that the solution components be fully coupled. This hybrid simulation capability should be embodied in a tool that is easy to use, especially in the context of mixing simulation methodologies that may have very different modeling requirements. To be useful, the capability should be efficient, and attention should be given to potential for hardware and algorithmic acceleration, including GPUs and traditional parallelization. A prime should demonstrate source code ownership of any computational electromagnetics software to be used in this project. PHASE I: Identify asymptotic and full-wave methods and software that are well suited to their respective large- and small-scale roles in sea-based target signature prediction. Develop and demonstrate prototype hybridization algorithms on multi-scale problems, considering their accuracy and practicality for robust implementation. Develop an implementation plan that shows how the mixed-scale hybridization would be configured through a graphical user interface (GUI) in light of the input requirements of the hybrid algorithm(s) and underlying solvers. PHASE II: Further develop the hybridization algorithms initiated in Phase I and implement the hybrid simulation capability in a prototype tool that includes a GUI for problem setup and output visualization. The GUI design should emphasize ease of use in the context of configuring hybridization for multiple large- and small-scale structures, including the surrounding sea state. Identify modeling and GUI improvements needed for commercialization. Identify and pursue initial hardware acceleration, including GPUs and clusters. PHASE III: Develop a commercial-grade software tool that provides an end-to-end hybrid modeling capability for this and other mixed-scale application areas, including a robust GUI and thorough user documentation. Fully implement hardware acceleration on GPUs and/or clusters. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The technology developed under this topic provides significant benefits to a variety of commercial and military radar sensing applications of mixed-scale targets, including aviation, boats and ships, spacecraft, ground vehicles, and fixed installations. REFERENCES: 1. Knott, E.F., Shaeffer, J.F., & Tully, M. T. (2004), Radar Cross Section, 2nd Edition, SciTech Publishing 2. Skolnik, M. (1990). Radar Handbook (2nd ed.). Columbus, OH: McGraw-Hill. 3. Jin, J-M, et al.,"A hybrid SBR/MoM technique for analysis of scattering from small protrusions on a large conducting body,"IEEE Trans. Antennas Propagat., vol. 46, no. 9, pp. 13491357, Sep. 1998. 4. Hodges R. E., and Y. Rahmat-Samii,"An iterative current-based hybrid method for complex structures,"IEEE Trans. Antennas Propagat., vol. 45, no. 2, pp. 265276, Feb. 1997.