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Apparent scintillation of subpixel targets imaged by focal plane arrays

For small unresolved or partially resolved objects the prediction of the performance of an IR sensor system is dependent not only on the optics and the atmosphere but also upon the geometry of the sensing elements within the detector. In particular this paper investigates the apparent scintillation caused by subpixel displacements of the detector from the optimum position is investigated. The effect is linked to the system point spread function and indeed the shape and size of the object. A simulator has been developed which can evaluate the effect of the shape and size of the sensing element, the optics, the viewed object and the atmospheric transmission, emission and background radiance. With the simulator it is possible to evaluate the effect that vibrations or pointing accuracy will have on the performance of the sensor systems for different types of targets. Results are presented which show that the variation in contrast of objects due to the shape and size of the active portion of a detector and the position of the target projection on the detector can be significant and should be taken into account when estimating system performance.