The detection of obstacles in surveillance systems using pyroelectric arrays

摘要

Arrays of pyroelectric elements are used in surveillance systems by focusing the radiation from a scene on to them and examining the output from the array. If an object is moved into the scene and left stationary, it will hinder the subsequent operation of the system by masking part of the scene from the field of view of the array; this fault condition may be detected by the following procedure. At intervals arrangements are made to move the image of the scene to and fro across the array using a suitable transducer and the outputs from the array are examined. The outputs from the array when the scene is in its normal condition and the image is moved across the array comprise a set of signals corresponding to a reference image, which may be compared with the corresponding outputs from the array when the image is moved across the array on a subsequent occasion. Change between the reference image signals and subsequent image signals are interpreted in terms of the introduction to, or removal of, objects from the scene.