GB1472854A - Differential optical polarisation detectors - Google Patents

Abstract

1472854 Television NATIONAL RESEARCH DEVELOPMENT CORP 7 May 1974 [11 May 1973 20 March 1974] 22586/73 and 12361/74 Heading H4F A differential optical polarization detector for inspecting crops, soil surfaces, finger prints, stains and dust disturbances on lunar or planetary surfaces, comprises a television camera 1, Fig. 1, which generates two video signals representing two views of the same scene which differ only in respect of their polarization characteristics, and means 12-16 which compare these two video signals over the whole scene on a point-by-point basis producing a composite video signal which is displayed in monochrome or colour and/or fed to a suitable data processor. In Fig. 1 the camera includes two camera tubes 2 and 3 associated crossed polarizers 10 and 11, the output signals being gamma corrected 12, 13, summed 15, subtracted 14 and divided 16 to produce the composite signal which represents the spatial variations of the degree of polarization of light from the secene viewed by the camera 1. This composite signal (or the difference signal from differential amplifier 14) may be displayed on a monochrome CRT 17, or the composite signal and the brightness signal from summing amplifier 15 may be fed via a colour matrix unit (Fig. 2, not shown) to a three-gun shadow-mask colour CRT display. The colour matrix unit codes the composite (i.e. polarization) signal so that when it has a value corresponding to a substantial negative value of the degree of polarization it is displayed as blue, when it has a value corresponding to a positive value lying in the lowest of eight ranges it is displayed as green, highest of the eight ranges as red, and for the six intermediate ranges as a graded sequence from green to red, and when it has a value corresponding to a small value (either positive or negative) the brightness signal is displayed in monochrome. In Fig. 3 the camera includes one camera tube 110 and a linear polarizer 113 which is rotated through 90 degrees by drive 114 between picture scans, the resulting sequential video signal being gamma corrected 116 and fed to the summing and differential amplifiers 15 and 14 directly and via a picture period storage device 119, e.g. a storage CRT. A monitor 117 may be connected as shown. A wavelength limiting filter may be disposed in the path of the incident light, which light may be in the infra-red or ultra-violet range. Reference is made to using a single camera tube having two separate photo-sensitive screens, and to using circular or elliptical polarizers instead of linear polarizers.