N112-119 TITLE: Improved Ship and Small Boat Classification Using Hybrid Synthetic Aperture Radar - Inverse Synthetic Aperture Radar (SAR-ISAR) Imaging

TECHNOLOGY AREAS: Air Platform, Sensors, Battlespace

ACQUISITION PROGRAM: PMA 265, F/A-18 Hornet Strike Fighter

OBJECTIVE: Develop innovative techniques to provide improved ship and small boat classification using hybrid synthetic aperture radar � inverse synthetic aperture radar (SAR-ISAR) imaging.

DESCRIPTION: ISAR is commonly employed to distinguish one class of ship from other possibly similar classes. It has traditionally been used to take advantage of the rotational motions of roll, pitch, and yaw induced on a ship by the sea. These motions can be substantial and thus provide a ready mechanism by which Doppler distributions across the target's structure can be consistently measured. The resulting two-dimensional image is a projection of the target's scattering centers onto a range versus Doppler grid, where the projection plane is defined as being parallel to the radar line-of-sight range vector and perpendicular to the effective axis of rotation of the target. Typically, the two most desirable image perspectives for ship classification are broadside profile and plan views. In practice, ships undergo a combination of roll, pitch, and yaw motions that yield a complex and continually changing multitude of visually unusual oblique projections.

In contrast to ISAR where we allow that the target itself is moving often with unknown velocities, SAR assumes the target scene is stationary, and calculates enhanced angular or cross-range resolution by analyzing subtle differences in range-rates due to the motion of the radar. From a classification perspective, supplementing ISAR imagery with target motion compensated SAR imagery can produce a product that is much easier for sensor operators to understand and subsequently, to be able to interpret them sufficiently to perform the classification task. The combination of simultaneously generating an ISAR broadside profile view and SAR plan view of a ship is very desirable. The challenge is to determine the basic kinematic and geometric characteristic in SAR imaging, the apparent and induced angles - yaw, pitch, and roll of the ship target during the observation time, to propose a linear frequency modulated SAR signal model, image reconstruction technique, and auto focusing procedure that can be implemented in real time.

PHASE I: Determine the technical feasibility of providing a hybrid SAR-ISAR ship and small boat imaging capability in real time. Develop a research, development, test and evaluation (RDT&E) plan addressing performance metrics, integration tasks, and human-system interface.

PHASE II: Design and demonstrate a prototype system in an operationally representative environment utilizing a Navy airborne radar system or suitable surrogate.

PHASE III: Transition the developed technology to appropriate platforms and the Fleet.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The method can be utilized in both commercial SAR and ISAR systems as well as homeland security applications.

REFERENCES:
1. Tang Li-bo, Li Dao-jing, Hong Wen, and Cao Fang, "High Resolution SAR Imaging of Moving Ships," Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. 2005 IEEE International Proceedings, 25-29 July 2005, pp. 3329-3332.

2. A.D. Lazarov and Ch.N. Minchev, "SAR Ship Target Imaging by Induced Complementary Movement," Recent Advances in Space Technologies, 2009. RAST '09. 4th International Conference on, 11-13 June 2009, pp. 441-446.

KEYWORDS: Synthetic Aperture Radar; Inverse Synthetic Aperture Radar; Target Classification; Ship Classification; Multi-Mode Radar; Small Boat Classification

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