Heterodyne Optical Correlator.
DEPARTMENT OF THE ARMY WASHINGTON DC
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A heterodyne optical correlator allows a correlation function to be computed for plural portions of a stereo pair of transparencies which is normalized to thus reduce the possibility of false correlation peaks. To obtain the correlation function, a pair of stereo transparencies are illuminated by an intense monochromatic light source producing an image at a common image plane in which a detector array is located. The relative path length, between source and transparencies, is periodically modulated producing at plural locations of the detector array plural alternating current signals representing the correlation between the amplitude transmittances at various corresponding locations on the transparencies for a given relative displacement between the transparencies. To normalize this correlation coefficient a second signal is produced by illuminating only one transparency and a corresponding third signal is produced by illuminating only the other transparency. Plotting the normalized correlation coefficient at each of the plurality of points in the transparencies as the relative positioning of the transparencies is shifted allows the correlation function and its peak to be determined.