N092-101 TITLE: Electromagnetic Scattering Effects of Sea on the Radar Cross Section (RCS) of Small Boats in Littoral and Deep Ocean Environments.

TECHNOLOGY AREAS: Sensors, Electronics, Battlespace

ACQUISITION PROGRAM: PMA �290, Maritime Patrol and Reconnaissance Aircraft

OBJECTIVE: Accurately simulate deep ocean and littoral environment sea surfaces to be used with modern computational electromagnetic (CEM) tools for detection, tracking, discrimination and classification of small boats.

DESCRIPTION: Attacks on the U. S. fleet by small boats in littoral environments is of great concern to the U. S. Navy. These boats may be in the presence of many other, similarly sized, but non-aggressive boats. This raises the threat level even more since it makes discrimination so much more difficult. For this reason, information on the scattering properties of such boats is highly desirable. A boat, however, is inseparable from the surrounding water and its presence has a noticeable effect on the ocean surface profile; thus, any effort at EM modeling and simulation (EMMS) must involve a sizeable patch of the surrounding ocean. Modeling tools developed for ocean surface scattering are too specialized to be used with modern CEM tools that predict the RCS of arbitrarily shaped targets, including small boats. Most CEM tools in the frequency domain (both exact-physics and high-frequency varieties, as well as hybrids of the two) require that the target be described in terms of surface patches. These patches, at this time, are either flat triangles or bilinear quadrilaterals. We need a similar description of the surrounding sea for gravitational, capillary and, possibly, near-breaking and breaking waves. This will allow for these CEM codes to perform RCS analysis of boats in the presence of the sea. We recognize the fact that the description of the sea in such a simple way may not provide as good information about sea scattering as a specialized code. It will, however, allows us to perform EMMS of a boat in the presence of the sea. In any case, the models developed should closely resemble the real situation. Simplistic models (e.g., a sinusoidal sea) will not be considered.

PHASE I: Using existing knowledge of sea behavior (littoral and deep ocean), develop methods that represent the sea surface in terms of patches, as described above. These patch models should be representative of sea conditions to be specified by the vendor. The end-user should be able to specify environmental conditions (as defined by vendor) and end up with a sea surface model. Account for the effect of the boat motion on the sea profile. Evaluate possible alternatives and formulate a final plan for Phase II.

PHASE II: Based on the Phase I results, develop a software program that generates different sea surfaces. The user should interface with this program through a fully developed GUI. Graphical outputs of the sea surface should be available. They should be based on a Non-Uniform Rational B-Spline (NURBS) description of the surface. The program should have the capability of turning such a surface into a mesh of flat triangles and bilinear quadrilaterals. It should also have the capability of generating a sequence of similar surfaces for pseudo-statistical analysis use. All models developed should be exportable at least as NURBS, triangles and quadrilaterals for use in established CEM codes. NAVAIR will advise on this matter. The deliverable will be a beta version of the code, together with a full electronic user�s manual and "getting started" examples.

PHASE III: Refine the code developed in Phase II. Finalize the technology and transition to the fleet.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The technology developed will find applications in detecting drug-trafficking small craft, and in large sea mammal migration.

REFERENCES:
1. https://www.feko.info/index.html

2. http://www.wipl-d.com/

3. http://www.saic.com/products/software/xpatch/

4. A. L. Maffett, "Statistical Description of Radar Cross Section". New York: Wiley, 1989.

KEYWORDS: Sea Profile; Sea Scattering; Computational Electromagnetics; Electromagnetic Modeling and Simulation; Small Craft; Detection, Tracking and Identification

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