Patent ID: 7193691

Claim:
A method for ignoring ground clutter in determining the presence of a missile seeker that retro-reflects incident light, comprising the steps of: projecting an ultrashort laser pulse having a predetermined nanosecond pulse width towards a search area to illuminate the retro-reflector of a seeker; detecting only returns from the search area having the same pulse width as the projected pulses so as to detect retro-reflective returns from the seeker and so as to reject pulse-stretched returns, the detecting step including using a focal plane array having a direct-reading focal plane array of photo detectors, each of the photo detectors having a threshold circuit coupled to the output thereof and set high enough to ignore low-level non-retro-reflected returns from the terrain illuminated by the laser; directly and simultaneously reading out each of the photo detectors for direct event detection of retro-reflected energy characterized by pulse widths virtually identical to the pulse width of the projected pulses, the readout being in a time short enough to obtain a reading from each of the photo detectors before the arrival of the next pulsed return, the time defining a frame; and without post-processing, determining from the readout that there is a retro-reflected return from a missile seeker and the position thereof if there is a signal from a single threshold circuit during the frame and if the signal from the single threshold circuit is not longer than the pulse width of the projected ultrashort pulse such that pulse width thresholding selects retro-reflected returns and ignores elongated returns from the illuminated terrain.