GB1431792A - Methods of modulating infrared radiation received by reconnaissance instruments - Google Patents

Abstract

1431792 Infra-red direction finders G PUSCH 2 April 1973 [26 April 1972] 15731/73 Heading H4D A method of modulating infra-red radiation received by a reconnaissance instrument utilizes a chequered lattice moved linearly across the target image field, the lattice being defined by two sets of intersecting parallel lines at least one of which makes an acute angle with the direction of lattice movement. The instrument Fig. 5 comprises a number of lenses 9 mounted on a hemispherical surface, which in combination with further lenses 19 image targets on to an image plane at which is stationed the lattice 13. Behind thelattice 13 are placed filters 23 and further lenses 15 focusing the images on to detectors 14 which are mounted on the hemispherical surfaces of a coolant chamber 28. The lattice is fixed on a drum 16 supported by a ring 7 mounted in a carrier ring 18 which is rotated by an electric motor (not shown). As the lattice moves across the image field, Fig. 1, each detector provides a modulated output whose phase relative to the rotation of the lattice indicates the position of the image on the lattice and hence the direction of the radiation source. The filters enable different wavelengths of infra-red to be used and the ratio of modulations at different frequencies may enable target identification. The lattices on the band 16 may be interspaced by semi-transparent areas which ensure an even average intensity is received by the detectors 14.