Abstract: A target identification system includes a target marker for selecting, and directing radiation at, a target, a weapon delivery system, and means for establishing a two-way communication channel between the two by reflection from a selected target. The communication is by infra-red laser and coded information is sent between the target marker and the weapon delivery system to identify the selected target.

Abstract: A loading probe for use in testing transducers includes an elongated body capable of simulating the normal acoustic impedance presented to a transducer to be tested by the medium in which the transducer is to operate. The main body of the loading probe has a tube made from a rigid material, and a rod having an elongated convergent portion extending into the interior of the tube so as to define a cavity which has a varying cross section. The cavity houses a core of material having a close match of acoustic impedance with the material of the tube and rod but a higher acoustic loss factor. The cavity is sealed. The active end of the loading probe carries a piezoelectric element having a planar form, and a protective end cap is bonded to the active end of the loading probe to enclose the piezoelectric element.

Abstract: The invention uses framestores for storing successive parts of three frames from the source of a video signal such as a camera, and a logical output selection unit arbitrates between the outputs for the frame to produce a reduced noise output to be fed to a T.V. monitor. If the noise of a pixel in the central frame is increased significantly compared to that in the first frame, the output of the third frame for that pixel is used to arbitrate between the two, for example, by selecting as the output that of the first frame if it is found that the output of the third frame is nearer to that of the first frame than to the second. Isolated noise specks are thereby reduced without the problems of motion smear.

Abstract: This invention provides a Raman laser wherein a light beam from a laser source (1) passes through a first chamber (3) and experiences Raman scattering, and then passes through a second chamber (9) and experiences further Raman scattering, such that the output of the Raman laser is frequency shifted. The first and second chambers may be distinct from each other enabling different types and pressures of gases to be utilised, or may be one and the same (20) providing a particularly compact arrangement. A Raman laser in accordance with the invention is particularly suitable for the production of light consisting of multiple rotational Raman orders, and particular embodiments enable frequency switching to be achieved and also provides arrangements which reduce the problems of boresight stability and gas circulation encountered with previous designs.

Abstract: The present invention provides a Raman laser wherein hazardous radiation from a pump laser source 20 is focused by lens 25 via a cell 27 containing a Raman active medium before passing to a absorbing beam dump 30. Lasing action is maintained within the cell 27 by the action of mirrors 29 and 26 which are respectively totally and partially reflective to radiation generated at the Raman wavelength, and which are both transmissive to the pump beam. A Raman beam exits the cell via partially transmissive mirror 26 is refocused by lens 25 and passes through to the output of the device 31. This configuration provides a Raman laser where the "eyesafe" Raman beam is generated in a backwards direction relative to the pump beam, so that during normal operation, or in the event that the optics breakdown, or conversion does not take place within the cell, the output beam would not be contaminated by potentially harmful wavelengths at a hazardous level.

Abstract: A collision warning signal for at least one vehicle is provided by transmitting from the surface of the earth a radio signal, receiving at the surface of the earth, a radio signal returned by a vehicle in response to the transmitted radio signal, determining an elapsed time between the transmitting of the radio signal and the receiving of the corresponding returned radio signal, determining the position of the vehicle at least in part in dependence upon the determined elapsed time, comparing the determined position of the vehicle with terrain data stored in a data base, and generating a warning signal based on the comparison if predetermined parameters are satisfied.

Abstract: A control system for, for example, a null-point gyroscope is provided in which, to minimize stiction, the control system is arranged to apply a decreasing oscillatory drive output to a precessed element of the gyroscope.

Abstract: To overcome the problem met with a video recorder for a conventional HUD camera, in which the HUD camera records the view received via the pilot's combiner and in which the symbols can appear too faint to discern in some conditions, separate sensors A and B are provided for the HUD and for the exterior view, and the outputs are electronically combined to produce a combined video signal for recording.

Abstract: Detector apparatus includes a dispersive prism (10) and a diffraction grating (11) of the type which produces only zero and first order diffraction patterns. Located behind the diffraction grating (11) so as to interact with the first harmonic content of the diffraction patterns is a Moire grating (12) having half the pitch of the diffraction grating (11). Detector means including at least two pairs of detectors (13-16) is located behind the Moire grating (12) to detect the presence of Moire fringes.

Abstract: A multiple-beam energy transmission system for the simultaneous transmission of at least two beams of energy directed in different directions from a single multi-element transducer assembly includes a signal source arranged to generate a train of successive signal pulses. Signal modifying circuitry associated with each element is provided for modifying the phase of each successive signal pulse by applying to each successive signal pulse a complex aperture weighting function, different phase shifts being applied to successive signal pulses, the phase shifts applied for one beam being unrelated to those applied for another. Control circuitry controls operation of the signal modifying circuitry such that the complex aperture weighting function applied to each successive signal pulse from the signal source by the signal modifying circuitry results in the radiation of the required beams of energy from the multi-element transducer assembly.

Abstract: To permit in-flight inspection of an aircraft engine, an imager views the front of the engine, and includes an image intensifier which is gated on and off at the engine speed. Small variations about the engine speed may be used to sweep all the blades into the field of view of an imager which does not view the whole of the front of the engine.

Abstract: An optical system, for the remote determination of the position and orientation of a body in a frame of reference, e.g. a helmet within a cockpit of an aircraft, comprises co-operating light emitting means and light sensing means. At least three of one type of said co-operating means are located on the body and scanning optic means are arranged to scan the frame of reference with a pair of planar beams. The planes of the beams are inclined to each other and are arranged to provide a light path between the co-operating means. A signal processing means is operative to provide a signal indicative of the position and orientation of a body and a time during the scan of each respective beam in which the beam is coincident with each of the said means mounted on the body. In one embodiment three light sensing means are located on the body and the planar beams are beams of light from a light emitting means.

Abstract: A zoom lens, for use in a telescope at infra-red wavelengths or single wavelength visible light, provides a magnification which may be adjusted to either of two predetermined values. The lens comprises a pair (14) of similar elements (15, 16) fixed relative to one another and each having an aspheric convex surface with the aspheric surfaces of the pair of elements outermost. The pair of elements (14) is located between the two image planes formed in the telescope and is movable between two conjugate positions.

Abstract: A method for correcting an integral signal representing the integral of an input signal derived from an accelerometer to eliminate the effects of errors in the input signal comprises sampling one or more signals which bear a functional relationship with the errors and subjecting the samples to a correction algorithmic process. The processed results are integrated and used to correct the input signal integral. Relatively few samples may be taken at below the Nyquist rate at random or pseudorandom intervals to provide an acceptable quantitive estimate of the error in the integrated input signal.The samples are spaced throughout the integration period by defining window intervals and taking one or more samples randomly in each window interval. Apparatus to practice the method include an integrator for integrating the input signal and a sample and hold circuit for sampling the input signal.

Abstract: A cooling fluid is circulated around a closed circuit including a heat source, for example by a pump. The system includes a heat exchanger for removing heat from the fluid. Valve means are provided which are operated by changes in volume of the cooling fluid to cause the fluid to bypass the heat exchanger when the temperature of the fluid is below a predetermined value.

Abstract: A current-to-frequency converter 12' (FIG. 3) for use with an accelerometer 10 comprises a storage capacitor 13 which receives the accelerometer current and develops a charging voltage, reset charging means 25 which delivers timed charges to offset the voltage by predetermined amount and voltage sensing means 14' which senses the charging voltage reaching positive or negative thresholds in order to initiate a reset and offsetting the voltage. The polarity of charging voltage at which reset is triggered determines that polarity threshold as being half the magnitude of the offset voltage but the opposite polarity threshold of greater magnitude so that the voltage on the reset capacitor avoids it.

Abstract: A radiation detector, including, a photodiode, has improved uniformity of sensitivity over the field of view because the receiving surface is provided by an optical diffusing layer, and the field of view is defined by a baffle arrangement, each internal surface of whichy is reflective. The baffle arrangement also defines a volume and the diffusing layer conforms to a part of the volume adjacent to the apex thereof. The diffusing layer may be provided by material, initially in liquid form, solidified in situ within the baffle arrangement. The receiving surface may be provided within a receiving head of the detector, spaced from the photodiode. Radiation may be transmitted from the receiving surface, whether part of a separate receiving head or not, to the photodiode by an optical fibre. An assembly of four consituent detectors, each having three orthogonally arranged mirrors, may together define a hemispherically shaped volume.

Abstract: The gyroscope had a closed optical path (10) defined by four reflecting surfaces (11, 12, 13, 14). Counter-rotating beams of radiation circulating around the closed path are produced by a gaseous active lasing medium executed over a gain region (15) to produce a discharge in the gas. A reciprocal dispersion element (18) is located in the optical path and a solenoid (23) is wound around part of the gain region to produce a magnetic field over that region. One of the reflecting surfaces (14) is a partially transmitting mirror which passes a small proportion of the radiation incident upon it, and detectors (19, 20) detect radiation in each counter-rotating beams passing through the mirror (14). The alternating current components of the outputs of the detectors are used to control a control circuit (22) so as to control the magnetic field produced by the solenoid (23).

Abstract: A closed path (14) around which two beams of laser radiation may pass in opposite directions is formed in a block (10) of material and is defined by at least three mirrors (11, 12 13). One of these mirrors (11) is partially transmissive of laser radiation in each beam and has detector means (17, 18) associated with it to derive electrical signals dependent upon the rotational forces acting on the gyroscope about an axis 19. A second mirror (12) is totally reflecting and is associated with a transducer (20) which continuously moves the mirror. Second detector means (21) is responsive to laser radiation in the two beams to derive alternating-current signals to control the transducer (20). Control means (22) respond to the direct-current component of the output of the second detector means (21) to maintain the intensity of the laser beams at a constant value.

Abstract: A circuit is provided to detect which of a simultaneous plurality of varying input signals has the dominant maximum amplitude. Two simultaneous input signals are compared with each other; or each of more than two simultaneous input signals is compared individually with a common, varying, comparing signal, provided in response to the summing of the input signals, and the subsequent scaling of the summation. The input signals, and a provided comparing signal, are different from each other, only, in amplitude. Normally there is expected, at least in relation to the input signal having the dominant maximum amplitude, to be a wide dynamic extent of amplitudes; whereas each signal supplied to a difference amplifier for such a comparison is arranged to have only a low amplitude, at least the dominant input signal being supplied so as to have only a range of amplitudes, as transmitted by an associated limiting amplifier in response to the receipt of the signal.