Three-dimensional pictures of industrial scenes applying an optical radar

For small scale ranging, a light beam, modulated with a wavelength typical for radio waves, is a suitable means of scanning. The ranging beam can be focussed to illuminate only a small spot. The diffuse reflection on the spot ensures that an echo appears. By applying phase comparison techniques to the ranging and echo beam the optical path length and thus the height of the illuminated surface element can be determined. By systematically deflecting the beam and thereby scanning the scene, a discrete height map is obtained. The realisation of such a small scale ‘optical radar’ is described, the main elements of which are a semiconductor diode laser for emission, an avalanche photo diode for detection, and a two-dimensional beam deflection mechanics for scanning. The typical performance is taking a picture of a volume of about 0·5 m × 0·5 m × 0·5 m within 1s, consisting of about 64 000 pixels.