Patent GB-1078282-A (GB)
Title: Optical instruments for indicating the path of a moving object
Inventor: RIDDLE CECIL
IPC: G01S3/786
Filed: 1964-05-22
Abstract: 1,078,282. Wave-energy position finding. NATIONAL RESEARCH DEVELOPMENT CORPORATION. May 18, 1965 [May 22, 1964], No. 21207/64. Heading H4D. In an optical path indicator, rays from the target enter a casing 1, pass along it to a parabolic mirror 2, are directed back to an obliquely mounted plane mirror 3, and are brought to a focus on a detector plane between the two mirrors. The mirror 3 is rotated by an electric motor 4 and the image of the target is caused to describe a circle 5 and cross two radially disposed detector strips 6, 7 which produce electrical signals at times dependent upon the angular displacements in altitude and azimuth of the target from a reference axis of the instrument. Also mounted within the casing 1 are two reference lamps 8, 9 beams from which are directed by a lens 10 on to the mirror 3 and are focused on another plane between the two mirrors in which are located two adjustable reference detectors 11, 12. As the mirror 3 rotates, the images of the lamps 8, 9 describe circles 14, 15 and when they cross the detectors 11, 12 electrical reference signals are produced for time comparison with the target signals. The detector strips 6, 7 may consist of lead sulphide, multi-element arrays with suitable filters so that they respond to infra-red radiation from targets. An optical telescope (18), Figs. 2, 3 (not shown), with cross wires may be mounted alongside the casing (1) to facilitate setting up the path indicator. The reference and target outputs may be used in the form of voltage pulses to trigger oscilloscopes and brighten their traces, respectively, whereby indications of azimuth and altitude are obtained, which may be photographed. Alternatively, by using electronic circuitry, the time intervals between the reference and target pulses may be converted into equivalent electrical voltages and be read upon suitably scaled instruments. The reference signals may alternatively be obtained from a synchronized pulse generator or by pick-off means associated with the shaft 13, Fig. 1, of the motor 4. In a modification, for use where only a small field of view is required, a parabolic mirror (2a), Fig. 4 (not shown), is obliquely mounted upon the shaft (13a) of an electric motor (4a), by which it is rotated, the plane mirror at the front end of the casing being omitted. In another modification, for use where a larger field of view is required, a large fixed parabolic mirror (2b), Fig. 5 (not shown), reflects radiation to a fixed plane mirror (19) at the front end of the casing, which reflects radiation back to an obliquely mounted rotary plane mirror (3b) adjacent the parabolic mirror (26). In some cases a lens focusing system may be used instead of the parabolic mirror, with a refracting material such as arsenic trisulphide for infra-red radiation. Means are described for making use of a reference marker lamp featuring sequential switching on alternate rotations of the mirror of the consequential outputs from the detectors with those from the target and, also, means for neutralizing the effects of extended spurious background illumination by making each detector of several sections and eliminating signals due to simultaneous energizations thereof.