Target acquisition modeling for contrast-limited imaging: effects of atmospheric blur and image restoration

Abstract

The incorporation of atmospheric aerosol and turbulence effects into visible, near-infrared, and thermalinfrared target acquisition modeling is considered. We show how the target acquisition probabilities and, conversely, the ranges at which objects can be detected are changed by the inclusion of atmospheric effects. It is assumed that images are contrast limited rather than noise limited, as is indeed the case with most visible, near-infrared, and thermal infrared sensors. For short focal lengths with low angular magnification, atmospheric effects on target acquisition are negligible. However, for longer focal lengths with large angular magnification, resolution is limited by the atmosphere, and this has a strong adverse effect on target acquisition probabilities, times, and ranges. The considerable improvement possible with image correction for atmospheric blur automatically in a fraction of a second is significant for contrast-limited imaging and is also discussed. Knowledge of the atmospheric modulation transfer function is essential to good system design and is also useful in image restoration for any type of target or object. Finally, a new target-transferfunction model is suggested that considers the overall image-spectrum target received by the human visual system rather than only the main harmonic detail as in the Johnson chart model. [ J. Johnson , in Proceedings of Seminar on Direct-Viewing Electro-Optical Aids to Night Vision ( IDA, Alexandria, Va., 1966), p. 177.]