Abstract

Apparatus for detecting the presence of an object within an area under surveillance employs an electro-optical emitter for directing light into the area and an electro-optical receiver for sensing light reflected from the object which originates from the emitter. The emitter emits light energy of a preselected wavelength and is modulated at a preselected frequency to provide the emanating light energy with a characteristic signature. Light reflected by an object within the area under surveillance is filtered and converted to an electrical signal which varies in accordance with the magnitude of the filtered light having the preselected wavelength and modulation frequency. A selected portion of the electrical signal is amplified by a band-pass amplifier and is synchronously sampled in accordance with the modulation frequency to determine the magnitude of the filtered light which originated from the emitter. The sampled signal is compared with a threshold value to determine whether an object is present within the area under surveillance. The emitter and receiver are covered by a transparent shield to protect them against foreign matter. An electro-optical detector monitors the accumulation of foreign particulates on the shield. The apparatus may be desirably used in vehicles to detect the presence of adjacent objects, particularly within the vehicle's "blind spots" and thereby avoid collisions.