Patent GB-1233007-A (GB)
IPC: G06V10/88
Filed: 1967-10-26
Abstract: 1,233,007. Optical correlation readout apparatus. MINISTER OF TECHNOLOGY. Oct. 22, 1968 [Oct.26, 1967], No.48760/67. Heading G1A. [Also in Divisions C4, G2 and H4] An optical correlation apparatus, e.g. for analysing radar, sonar or seismological signals includes, a pattern-forming means Q 1 -Q n , Fig.4, responsive to signals received at a plurality of positions A1 to An spaced apart in a circular formation for forming an input signal pattern 30 substantially representing a graphical plot of the signals, each plotted against two co-ordinates, of which one co-ordinate represents the time of reception of the signal, and the other co-ordinate represents the azimuthal bearing relative to the centre of the circular formation of the position at which the signal was received, a laser 8 to illuminate the input signal pattern 30, a first convergent-lens system 11 for forming in a reference plane 12 a pattern effectively representing a Fourier transform of the input signal pattern 30, a holographic transparency 34 located in the reference plane 12 and effectively representing a Fourier transform of a reference pattern derived from a reference input signal pattern such as would be formed by the response of the patternforming means to signals emanating from a single point source, a second convergent lens system 14 for forming in a image plane 35 a pattern effectively representing a Fourier transform of the light distribution formed in the reference plane 12 as modified by viewing through the holographic transparency 34, and detector or display means D1-Dn for facilitating observations of the pattern formed in the image plane 35, and wherein either the reference pattern or the input signal pattern is extended over an azimuthal co-ordinate range equal to at least two complete circuits of the circular formation. Preferably it is the reference pattern 34 which is so extended. The patternforming means Q 1 -Q n  may be a multi-channel optical modulator, with each channel responsive to a separate one of the signal receiving positions A1-An. Such modulators may be quartz Piezoelectric transducers arranged along one edge of a multi-channel sonic light modulator cell filled, e.g. with distilled water or methylalcohol. A channel separation mark 33 is used to ensure that the output rays are those affected by only one of the acoustic waves. The acoustic waves move continuously downwardly over means 30, and the display in image plane 35 moves upwardly. The line of detection of a display spot, as it passes upward across the row of detectors D1-Dn relative to the time cycle of the transmitter of the radar system A1-An indicates e.g. the range of the target. Each detector D1-Dn detects spots resulting from targets in a range of azimuthal directions determined by its size and position in the row. The detectors may include image intensifiers and electrical outputs from then may be applied to display means which may include a computer or tracking units or both. In an alternative embodiment Fig. 1 the signals from spaced positions M1-Mn received by a scanner 1 are fed into an oscilloscope and continuously recorded on a sensitive medium 3. This recording is then made into a permanent or semi-permanent translucent pattern by any known photographic, photochromic or thermoplastic recording technique. The recording is cut into sheets each containing a complete set of all the reflections of one transmitted pulse received from a target by means M1-Mn within the surveillance area. The reference pattern 34 is formed by drawing a representation of for example, a signal pattern produced by signals from a target whose azimuthal bearing is zero. This pattern is then introduced with a hologram forming apparatus and a hologram mode, which when developed becomes the reference transparency 34. The detector or display means may be a screen located in the image plane and which is coated with a fluorescent material. Examples of suitable holographic transparency reference patterns are given.