A technique is described for suppressing the lower spatial frequencies in the object using an optical system with a time-varying MTF. The technique is applicable to imaging radiometers operating in the infrared region. The required variations in the MTF are produced by causing the image to move in a programmed sequence of small amplitude circular gyrations on the face of the detector. The gyrations are performed at a frequency high compared to the system frame rate. A series of calculations are described which indicate that, at low spatial frequencies, average suppression ratios of at least 500 to 1 can be achieved with this technique.
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Theodore Zehnpfennig, Saul Rappaport, Richard Wattson, "Background Suppression With Variable Modulation Transfer Function (MTF) Imaging Systems," Proc. SPIE 0253, Modern Utilization of Infrared Technology VI, (17 December 1980);