Optical Modeling and Simulation of Subpixel Target Infrared Detection

Main performance characteristics of defensive systems against incoming threats such as RPGs, rockets or missiles, are the capacity for early detection over longer ranges with high probability and low false alarm rate, the short time recognition and declaration of the threat and its tracking and location capabilities. Infrared multiband imaging is one of the electrooptic techniques used to detect, track and classify the propelled threats through discrimination of the exhaust plumes and emitting body against other background sources. Target is in most of the cases, an unresolved object and appears in the detector smaller than a pixel or covering a few pixels. However, launching eject and boost, and sustained propulsion can be sensed during flight. Before the system design, an analysis is carried out to constrain key performance parameters for defined use cases and scenarios. The work presents a mixed approach for the infrared imager, using commercial key performance parameters, experimental measurements, parametric and ray-tracing based modeling to fully characterize main radiometric, angular an temporal responses. Optical subpixel detection considers the intrinsic parameters of the wide field of view optics and focal plane array sensor such as, the angular distortion, the point spread function (PSF) or, the detector spatial and temporal noise and the radiometric response. Extrinsic inputs to the system are the radiative threat and background and the atmospheric transmitting media where the terrain and sky types and the absorption, scattering and turbulence influences the effective contrast and range. The infrared dynamic signatures of several threats have been simulated with eject, boosting or sustained propulsion and the nose aerodynamic heating embedded into a real infrared scenarios. The overall model generates a synthetic environment of the sub-pixel target signature against the background clutter taking into account the frame-to-frame evolution according to the expected trajectory of the propelled threat. So, it is possible to simulate at sensor level, the signal and spatial timeframe of the fast dynamic target and tailoring design parameters for a better signal to clutter ratio and range performance. Additionally, final simulated results can be used as an input for development of detection and tracking algorithms.