An optical radar pilot warning indicator

A proposed pilot warning instrument based upon the principle of an optical radar is described. Target cross section enhancement, through the use of a passive retroreflector, allows a small semiconductor light-emitting laser diode to act as transmitter. A split scanning beam together with integrated circuit signal processing gives the "tau" time of each target thus providing an alarm only in the case of a threat. System parameters are selected to meet a single scan detection probability of 97 percent for targets under minimum visual flight rule conditions while maintaining a "worst case" false alarm rate from solar illuminated clouds of less than one per hour. A significant advantage of the system lies in the noncooperative, inherently fail-proof nature of the target enhancement device, the Retro. In any encounter, it is desirable that "own" aircraft depend to a minimum extent on the state of repair and adjustment of the "intruder\´s" equipment. The relatively low cost triple mirror array closely fills this requirement.