Patent GB-1199333-A (GB)
Title: Method and Apparatus for Deriving and Processing Topographical Information
Inventor: DISHINGTON ROLAND HANLEY
IPC: G01S17/89
Filed: 1967-10-19
Abstract: 1,199,333. Range determining. TRW Inc. 19 Oct., 1967, No. 47698/67. Heading H4D. Specification describes a method of obtaining a photographic contour representation b, Fig. 14 of terrain by means of light pulses emitted in a fan beam 13, Fig. 1, by an aircraft &c. 10 and gating the echo signals by means of a plurality of time gates, each corresponding to a contour height, and each gated signal portion giving rise to a respective part of a contour 75. Thus a Q-switched Laser 20, Fig. 1, under the control of clock 22 prodcues a 5ns light pulse every 2ms, which is formed into a fan beam 66 by optics 24. The speed of the aircraft is ideally such that the areas 14, 16, 17 of the ground illuminated by successive pulses are abutting. The image of the illuminated strip of terrain is collected by optics 70 and directed to the photo cathode 80 of photo-emissive tube 40 by means of a rectangular bundle 128, Fig. 13, of light fibres. The image on the cathode is periodically gated through to a fluorescent screen 88 by means of 100 Mc/s. gating pulses 79, Fig. 4, from generator 26 and clock 22. The first received echo 81 of the Tx pulse is from the highest part of said illuminated strip and will produce a latent image at a corresponding point on the cathode 80. Each gating pulse 79 represents an incremental height or contour spaced by 2À5 ft. Half the echo pulse is seen to be gated to the screen 88 whereby a contour line mark is just produced (production necessitating the gating of half or more of an echo pulse). A strip section of the image b Fig. 14, is thus formed on the screen 88 and is transferred to film 32, moving in synchronism with the aircraft's motion, by means of a bundle of light fibres 132. The countour image b merely indicates that a part of the terrain on contour 72 is 2À5 ft. higher or lower than a part on contour 74. To give an indication of the aircraft's altitude above the centre line 12, Fig. 1, of its path, a light fibre probe 130 (44 in Fig. 1) is positioned at the centre of the bundle 128 and directs the echoes from said centre line to a photosensor 46 to produce a pulse which causes a counter 49, started by the transmitted pulse, to read out its count, proportional to said altitude, to the recorder 28. The altitude may be recorded on the film in a digital form C, Fig. 14, on an analogue form C<SP>1</SP>, Fig. 15. Every 100 transmitted pulses a profile 67, 69 is taken across the strip. Deflection plates 84 and 86 are provided, supplied with the voltage of Fig. 6. For the first 100 pulses the voltage is slightly negative whereby the strip image is formed on the right-hand part of screen 88, Fig. 1 (said strip being perpendicular to the plane of the Figure). With the 101st pulse the voltage goes positive for 20Ás and has 40 ramp portions 63. Each part of the strip image is deflected to the left by an amount depending on its time of occurrence or altitude (range) of the corresponding part of the terrain strip. Profiles 67, 69 are thereby produced and transferred to region a of the film by light fibre bundle 134. Every sixth contour line 73, 75 may become a " course " contour line by being emphasized. The laser pulses may be concentrated in bursts of 100, Fig. 16 (not shown), with mirrors (150), (154) in the transmitting and receiving beam paths rapidly swinging to distribute the pulses evenly along the terrain. To simplify the optics a conical transmission beam may be used, Figs. 18, 19, 20 (not shown), resulting in consecutive overlapping annular areas of illuminated terrain.