Non-uniformity Infrared Sensors

TWO RELATED PROBLEMS WHICH LIMIT THE PERFORMANCE OF STARING INFRARED SENSORS ARE DETECTOR NON-UNIFORMITY AND INADEQUATE RESOLUTION. REMOVAL OF DETECTOR AND READOUT NON-UNIFORMITIES ("FIXED-PATTERN NOISE") IS ESSENTIAL FOR THE DETECTION OF LOW-OBSERVABLE TARGETS IN CLUTTERED BACKGROUNDS. ADEQUATE RESOLUTION IS ESSENTIAL FOR SEPARTING CLOSELY-SPACED ONJECTS AND MAKING ACCURATE MEASUREMENTS OF THEIR LOCATIONS. THE CONVENTIONAL APPROACH TO NON-UNIFORMITY CORRECTION IS CALIBRATION OF EACH DETECTOR BY INTRODUCING TWO OR MORE REFERENCE SOURCES INTO THE SENSOR FIELD OF VIEW. THIS APPROACH IS EFFECTIVE, HOWEVER, ONLY WHEN THE DETECTOR-TO-DETECTOR NON-UNIFORMITIES REMAIN CONSTANT OVER TIMES LONGER THAN THAT BETWEEN CALIBRATIONS. THIS IS OFTEN NOT THE CASE DUE TO TEMPERATURE CHANGES, SYSTEM INSTABILITIES, 1/F NOISE, ETC. THE ONLY STRAIGHTFORWARD METHOD TO INCREASE RESOLUTION IS TO INCREASE THE SIZE OF THE OPTICAL APERTURE AND DECREASE THE DETECTOR SPACING. THIS IS EXPENSIVE SOLUTION IN TERMS OF WEIGHT, COMPLEXITY AND COST. WE HAVE DEVELOPED AN ELEGANT NEW SOLUTION TO THESE PROBLEMS BASED ENTIRELY ON PROCESSING OF THE SENSOR OUTPUT SIGNALS. WE USE MULTIPLE IMAGE FRAMES, AND TAKE ADVANTAGE OF THE SENSOR AIMPOINT WANDER CAUSED BY JITTER, RESIDUAL TRACKING ERRORS, OR DELIBERATELY INDUCED MOTION. SUCH WANDER CAUSES EACH DETECTOR IN THE ARRAY TO VIEW MULTIPLE SCENE ELEMENTS, AND EACH SCENE ELEMENT TO BE VIEWED BY MULTIPLE DETECTORS. IT IS THEN POSSIBLE TO FORMULATE A SET OF SIMULTANEOUS EQUATIONS FROM WHICH CORRECTION PARAMETERS FOR EACH DETECTOR AND THE BRIGHTNESS OF AN OVER-RESOLVED SET OF SCENE PIXELS CAN BE COMPUTED. THESE RESULTS ARE ACHIEVED FROM PROCESSING THE SCENE ITSELF AS VIEWED BY THE SENSOR FOR A BRIEF PERIOD, AND DO NOT INVOLVE THE USE OF REFERENCE SOURCES.