Abstract: A method and apparatus for making reflection holograms wherein a film (27) of light sensitive material in which the hologram is to be formed is rotated about a first axis (Y--Y) which is itself rotated about a second axis (X--X) which intersects the first axis at a position (Z) spaced from the film so that a coherent light beam (29), which is directed onto the film and whose axis passes through the point of intersection of the axes, scans the film in a pattern of overlapping narrow bands. The bands may be rectilinear or circular.

Abstract: An electric circuit module arrangement adapted for mounting in racking comprising a number of modules (C) secured together in side by side relationship. Interconnections (127b, 169) between the modules are provided at one end of the module arrangement and form part of the arrangement while connectors (127a) for establishing connections with other modules outside the arrangement via a wiring arrangement separate from the module arrangement, e.g. supported on the racking, is provided at the other end of the module arrangement.

Abstract: An angular position sensor for sensing the relative angular position of a helmet worn by a passenger in an aircraft with respect to the aircraft is disclosed. The sensor includes three spaced linear photodetector arrays fixed to the aircraft, and a light source mounted on the helmet and arranged to produce a light beam which rotates cyclically about an axis in the helmet so as to successively irradiate a photodetector within each array within each cycle. A sensor attached to the helmet produces a time datum signal during each cycle. A computer uses the location within the arrays of the irradiated photodetectors, and the relative timing of the irradiations with respect to the time datum to provide the required azimuth, elevation and roll angles of the helmet.

Abstract: A tire temperature measurement apparatus comprising a microwave receiver (9 or 11) sensitive to electromagnetic radiation in a waveband in the frequency spectrum 10 to 100 GHz and a directional antenna (5 or 7) coupled to the receiver input and responsive to radiation from a predetermined surface area only of the tire (1 or 3).

Abstract: A night vision system comprising a helmet (1) having a transparent visor (13 or 15) before or movable to a position before the eye positions (IL, IR) of an observer wearing the helmet and a night vision device (19) having two eye pieces (22L, 22R), one for each eye, supported dependant from the helmet (11) so as to present the eye pieces (22L, 22R) of the device (19) at a short distance before the helmet wearer's eye positions and the visor (13 or 15). The device (19) is supported by means of a four-bar linkage arrangement (A,B,C,D) which constrains the eye pieces (22L, 22R) for rotational movement about the respective eye positions (IL, IR) between different operative positions, and so that the eye pieces (22L, 22R) do not make contact with the visor (13 or 15) during eye piece movement.

Abstract: A magnetic field sensor in the form of an arcuate element comprising two superimposed strips of material is described. The magnetostrictive constant along the longitudinal axis of one of the strips is greater than that of the other strip, the latter strip carrying at each end a post. In use of the sensor a single mode optical fibre is attached to the element via the posts such that the part of the fibre between the posts extends along a chord of the arc defined by the element. A variation in applied magnetic field in the plane containing the arc gives rise to a variation in the part of the fibre between the posts. Light passing through the fibre is thus phase shifted by an amount dependent on the value of the applied magnetic field.

Abstract: A display arrangement for a head-up display system e.g. for an aircraft, wherein the combiner (13) comprises a first tuned reflective optical film (39) through which an observer (14) views a distant scene and second and third tuned reflective optical films (41 and 43) positioned outside the observer's view of the distant scene through the first film. Light from a projector (11) passes first through the nearer (43) of the second and third films, is then reflected at the other (41) of the second and third films, is then reflected at the nearer film (43) and then passes through the other film (41) to the first film (39) where it is reflected towards the observer. The three films are normally designed to provide the combiner with a desired optical power, the one (43) of the second and third films nearer the projector suitably being concave toward the other (41) of the second and third films for this purpose.

Abstract: An optical method of measuring displacement and a sensor for use in the method comprising a light guide and a concave reflective element positioned such that one end of the light guide is at the center of curvature of the reflective element. The reflective element has different regions having different reflection coefficients for light within two different wavelength bands. A member is interposed between the end and the reflective element, the member having light transmissive properties which vary spatially over the member in a direction transverse to the optical axis of the element. The member and reflective element are supported so as to allow them to be displaced relative to one another in a direction transverse to the optical axis of the element.

Abstract: A retractable airborne radar pod housing a radar scanner is provided with inflatable portions which when deflated allow the pod to be retracted into the aircraft and when inflated form an aerodynamic shape.

Abstract: An aircraft attitude display device comprising: a circular array of radially extending selectively activatable display elements (5), the radially inner ends of which constitute a boundary defining a central space; within the said central space, a fixed aircraft symbol (7); and means for selectively activating the said display elements in accordance with aircraft attitude so that the selected display elements form a visible pattern, e.g. a sector of the array, bearing a geometrical relationship with respect to the aircraft symbol indicative of the aircraft attitude.The device is suitable for implementation using liquid crystal display technology to give a stand-by display of aircraft pitch and roll which is readily understandable by pilots since it is similar to the display given by conventional rolling ball action aircraft attitude instruments.

Abstract: An optical projector (11) for a head-up display wherein light from a data source (15) passes through a first lens arrangement (23) and then into a wedge-shaped body (27) via a first face (29) of the body wherein the light is, in turn, internally reflected at second and third angled faces of the body (35 and 33) and then exits the body at the second face (35) to pass via a second lens arrangement (25) to the system combining (13) in a direction at an angle to that which light enters the body.The arrangement of the projector facilitates the projector having lateral dimensions dictated by the data source (e.g. a CRT) rather than the optical elements of the projector.

Abstract: A guidance method which enables a moving body to be guided to a predetermined location by allowing the body to view its surroundings and to compare the viewed scene with a reference pattern stored on the body. A number of individual reference patterns are stored, and each reference pattern corresponds to an area of the surroundings which is very much smaller than the field of view and thus the body identifies its position by correlating its field of view with one of the reference patterns. To enable the body to identify its position, even if it deviates from an expected path, a number of reference patterns are laterally displaced from the expected path. The extent of the lateral displacements reduces with decreasing distance from a predetermined location to which the body is to be guided.

Abstract: The system relates to a telescope having optics and a scanning head which images a two-dimensional field of view point by point onto a localized thermal sensor. An aperture stop is mounted within the telescope housing and at least part of it is within the field of view of the sensor. The temperature of the stop is controlled by means of Peltier thermo-electric modules so that it corresponds to the average temperature of the external field of view. This prevents halation or blooming which would result from extreme temperature contrasts. The vignetting which occurs when the aperture stop is within the field of view gives an increased magnification for a given size of objective optics, and the benefits outweigh the corresponding reduction in thermal sensitivity.

Abstract: A method and apparatus for determining the relative positions of a first object (1) and a second object (3). The method comprises illuminating the first object (1) so as to produce a shadow (17) of the first object on a surface (15) lying at a known position with respect to the second object (3) and forming a two dimensional image of a scene including the surface (15). The distance between the position of the shadow (17) and a reference position (19) in the two dimensional image is monitored, and this distance is used to derive information relating to the relative positions of the first object (1) and the second object (3).

Abstract: A data processing arrangement is designed to handle two dimensional data arrays. An operation is performed on each element in th data array which is partially dependent on the nature of the neighboring data elements which surround it. In this way particular characteristics of the two dimensional array can be detected or removed, i.e. picture edges can be detected or noise can be removed. Each element and its neighboring elements are used to address a store which holds the result of performing the corresponding operation. In practice, the two dimensional array of data arrives as a continuous data bit stream so that a window corresponding to a particular element and its neighboring elements is scanned systematically across the two dimensional array. The arrangement is capable of handling a continuously arriving data stream. The operations performed on the data can be readily changed by altering the nature of the stored results.

Abstract: An encapsulated assembly of electric components (12) on a board (11) wherein the board and components are encapsulated in a mass of silicone rubber (17) which rubber mass is in turn encapsulated in a mass of rigid epoxy resin compound (21) which is partially supported by pillars (13) which are mounted on the board and extend outwardly to the surface of the mass of foamed silicone rubber, electrical connection to the components being provided by connector pins (15) extending through both encapsulations.

Abstract: A communication system using a control bus and an audio bus to interconnect operator positions and radio positions. Each position is allocated, by a timing circuit, time slots on the control bus during which it applies digital words to the control bus indicating its own identity and information to be transmitted to other positions. Because data applied to the control bus by the operator positions is time multiplexed, requests from operator positions for a particular radio facility are dealt with in turn by the radio positions so that operators at the operator positions cannot compete for the same ratio facility. The need for a general purpose computer and its associated software is avoided. Each radio at the radio positions is able to communicate to the operators at the operator positions its current mode of operation so that the operators can always be sure that the system is operating correctly.