Detecting position of aircraft flying overhead for accurately recording registration markings

摘要

An object detection system includes passive sensors 6 for receiving electromagnetic radiation from a moving object, such as an aircraft, in a field of view and generating intensity signals representative of the received radiation. Images of the radiation at successive periods of time are generated from the intensity signals. A processing system 8 processes the images to obtain a background image and subtracts the background image from the images to obtain respective difference images. Pixel values across a dimension of the difference images are summed to obtain respective image profiles, and by obtaining the difference between successive image profiles difference profiles are generated. The difference profiles represent time derivatives of the image profiles and provide a differential signature representative of the position of the moving aircraft. The processor generates an image acquisition signal to the controller 14 on the basis of the differential signature.