GB1444518A - Synchronous thermal imaging system - Google Patents

Abstract

1444518 Infra-red scanning system HUGHES AIRCRAFT CO 27 March 1974 13603/74 Heading H4F An infra-red scanning and display system for use in an aircraft such as a helicopter for obtaining a thermal image of the terrain comprises a vertical array of detectors across which an image of the terrain is swept (i.e. azimuthal scan) by a mirror, the resulting simultaneous video signals from the linear detector array being passed to a time division multiplexer type processing arrangement operable in real time to sample the video signals and to render the samples sequential so that they correspond to a vertical image line scan, and the resulting vertical raster scan video signal being displayed, e.g. on a CRT, under the control of synchronizing pulses generated in the processing arrangement. The time division multiplexing is effected in two stages, for example in the embodiment described an N detector linear array is divided into four groups each including every fourth detector, i.e. N/4 detectors, the sampled outputs from the detectors of each group being first rendered sequential and then appropriately time division multiplexed with each other. An interlace mirror is including in the optical scanning system so that successive field scans are interlaced, i.e. an interlaced display of vertical lines is produced. An AGC circuit is associated with each detector and is responsive to a modulated reference signal derived thereby in response to a modulated automatic responsivity control light source. Any effect of a cold narcissus image formed in response to the detector array (which is maintained at a low temperature) by reflection from optics in the system is cancelled by providing a hot infrared narcissus vertical-image line source, a proportion of the output of which is modulated (by a modulating slit and beam splitter arrangement) to comprise the AGC control source. Adjustably positioned horizontal and vertical sight-lines (boresights) may be added to the processed video signal and displayed, the optical imaging telescope-type system including an adjustable vertical boresight mirror and the horizontal boresight being generated electrically in response to the horizontal sync pulse. In addition the optical system includes adjustable optical elements for narrow and wide field of views, and an adjustable pointing mirror.