Abstract: A direction finding system for infrared radiation includes a set of four detectors uniformly positioned about the Z axis of a cartesian coordinate system with individual ones of the detectors having radiation detection surfaces facing the Z axis and being inclined relative to the Z axis. The detectors are inclined relative to an XY plane of the coordinate system. Signals of the detectors are fed into computer storage to permit computation of the direction of a source of radiant energy relative to the Z axis based on a ratio of magnitudes of the signals of the detectors.

Abstract: Retroreflector (10) has a base (12) with an even back surface (24) and an uneven forward surface (14). The uneven forward surface is illustrated as grooved with one of the grooves shown at (22) with groove sides (30) and (32). The uneven forward surface (14) is coated with retroreflector elements (16) so that incident light from almost 90.degree. to the normal is retroreflected.

Abstract: A direction finding system for infrared radiation includes a set of three detectors uniformly positioned in an XY plane about the Z axis of a cartesian coordinate system with individual ones of the detectors having radiation detection surfaces being normal to the Z axis. A set of three mirrors have front and back reflecting surfaces which are parallel to the Z axis, the mirrors being uniformly distributed among the detectors. Signals of the detectors have magnitudes dependent on the sum of direct radiation and radiation reflected by adjoining mirrors. The detector signals are fed into computer storage to permit computation of the direction of a source of radiant energy relative to the Z axis based on a ratio of magnitudes of the signals of the detectors.