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Abstract

A method and system of image modulation detection of an aircraft or missile exhaust plume or explosives by time sequence differentiation is provided. The method comprises the steps of forming two sequential images of the field of view in which an exhaust plume to be detected is located, and forming a differential image from the sequential images showing components of the aircraft's exhaust plume that are modulating at a rate greater than the frame rate of the detection system. The detection system permits a selection of frame rates so that unwanted (non-modulating) items in the field of view may be eliminated from detection by the threat warning system. The nonmodulating components such as the sky, hills, and even the missile body are eliminated from the differential image. Only the plume remains and only the plume is detected. Each image is formed by a plurality of pixels, wherein each pixel images a portion of the field of view. The value of each pixel in one sequential image is subtracted from the value of the corresponding pixel in the other sequential image to produce a value for a resultant pixel. The differential image is formed by imaging the resultant pixels that have a non-zero value, wherein the differential image shows components of the aircraft's or missile's exhaust plume that are modulating at a rate greater than the frame rate of the detection system. If false targets are detected by the system, the frame rate may be increased to decrease the time period between the formation of the first and second sequential images thereby eliminating targets having a lower modulation frequency.

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