Patent US 4,124,865

A reticle superimposed upon an observation scene is detected by electronically discriminating the reticle from the rest of the observation scene to thereby define a coordinate system. The reticle is identified in an observation scene by recognizing that all reticle signal return elements fall on a straight line, that each reticle return will have a substantially uniform amplitude or pulse height, and that each reticle will have a predetermined predictable line thickness or pulse width. The discriminating system and method utilized first gates the video to detect returns within only selected portions of the observation scene. The "blackest" level within each video gate is then determined and a reference level close to it is established. All signals below the reference level are then purged. Finally, the pulse width of each resultant signal and its associated location within each sensor sweep is determined and tested for correlation with the resultant signals of a plurality of sequential sensor sweeps. Azimuth and elevation reticle locations are defined when such correlation exists.