GB1184633A - Image Spectrophotometer. - Google Patents

Abstract

1,184,633. Image spectrophotometer. TRW Inc. 16 Feb., 1968, No. 7730/68. Heading H4F. [Also in Division G1] The Specification describes apparatus whereby a viewed scene, Fig. 1, may be scanned and displayed at one or more wavelengths whereby visually similar objects, e.g. growing vegetation 13 and cut vegetation 22 camouflaging an object 15, may be distinguished by means of their different reflective spectral characteristics, Fig. 2. Thus an image of a strip portion 66, Fig. 7, of the scene is dispersed by refractive or diffractive means in a direction normal to the length of the strip and the resultant image, Fig. 8, scanned along one or more wavelengths (horizontal lines) the resulting video signal being used to intensity modulate linearly scanned cathode-ray tube display means. The strip portion 66 is selected by slit 31, Fig. 4, having the scene focused thereon by lens 32. The strip is diffracted by grating 35 and the image, Fig. 8, focused on camera tube 37. When the apparatus is used in an aircraft 60, Fig. 5, the movement of the aircraft, together with the synchronized oscillatory movement of mirror 30, Fig. 4, enables consecutive abutting strips of scene to be scanned by successive field scans of camera 37. The raster of camera 37 only need comprise a small number, e.g. twelve of lines since only a one-line scan of the correct wavelength will enable growing and cut vegetation &c. to be distinguished. The video signal from the camera resulting from such a one wavelength (line) scan, is fed to intensity modulate the line sweep of display 131, Fig. 11, the position of the line corresponding to the position of the strip 66 in the scene. A representation of the entire scene may thus be built up at said wavelength. Using three wavelengths (lines) and feeding the corresponding three video signals to the three modulating inputs of a three colour display tube 132, a corresponding colour display may be produced. By selecting the relative intensities of the colours, growing vegetation may show as white and cut vegetation as red. The video signals may alternately be stored at 130 or digitally analysed and stored by means 140 and 141. Compensation for the non-linear characteristic, Fig. 13 (not shown), of the camera tube 37 may be carried out by computer 155 and the normalized digital data stored at 156. To increase the wavelength resolution of the apparatus, the camera raster may be compressed in the frame direction, Fig. 10 (not shown). Mechanical details of the apparatus are given, Figs. 14, 15, 16, 17, 18, 19 (all, not shown).