Abstract: This process for detecting the coming interposition of a mask between an aircraft (A) and a target (C), particularly in a laser-guided weapon firing system, wherein the aircraft has an automatic target tracking system providing an image of the terrain on which the target occupies a permanent fixed position, consists in detecting, during a turn carried out by the aircraft, the points M of this image, marked by their elevation i.sub.m -i.sub.c with respect to the target C, situated in a zone such that i.sub.M -i.sub.C <0 and having an angular progression velocity, with respect to the target, opposite to that of the other points in that zone at the same altitude as the target.Application in particular to laser-guided weapon firing systems.

Abstract: For carrying out an interrogation a position modulated laser light wave is used. A key word is displayed in an interrogator and coded in accordance with a cyclic code, for example Golay's code. This coded key word is used for modulating the laser wave. In the responder the same key word is displayed and coded in the same way. After reception and demodulation each message is compared in a correlation circuit with the local reference word. The correlation method used allows parasite pulses to be taken into account and the word received to be validated with a given security threshold.

Abstract: A method and device are provided for assisting in height holding in air navigation, consisting, for any point (M) of the image of the landscape flown over by the aircraft (A), located by its angle of elevation (.theta.-p) with respect to the speed vector V of the aircraft, and situated in a zone between a lower elevational limit (.theta..sub.1 -p) and an upper elevational limit (.theta..sub.2 -p), in the trajectory of the aircraft, in detecting a possible deviation between the angular speed .OMEGA. of movement of this point with respect to the aircraft, depending on the height (h,H) of subsequent crossing of this point by the aircraft, for identical piloting conditions, and an angular reference speed of movement (.OMEGA..sub.o) corresponding to a reference height (h.sub.o,H.sub.o) of subsequent crossing by the aircraft of a point having the same elevation (.theta.

Abstract: A digital data transmission system by modulating a coherent light wave is provided using modulation of the MSFK type with N frequencies for modulating the light wave. The transmitter comprises a coherent light source, a modulator, an output optical means and an MSFK modulation signal generator. The receiver comprises an input optical means, local light wave source and a heterodyne mixer for creating an electric signal of intermediate frequency. A demodulation and detection circuit comprises filtering means for separately selecting the N frequencies before detection. A processing cirucit puts the data back into its initial form. A circuit for compensating for the drift of the light sources is used for preserving lock on to the intermediate frequency.

Abstract: A light retro-reflective responser and data modulator arrangement which, in particular, allows expected incident radiation to be reflected back with no contour field within the operating field and which enables an optical modulator of very small size to be used. It comprises a retro-reflective system formed by an optical objective and in the corresponding focal zone, a lens, an electronically controlled optical modulator, and a reflective mirror, the two latter items being produced as layers deposited on at least one face of the lens and preferably on the plane face of a plano-convex lens.

Abstract: An arrangement for measuring by correlation the lag produced by the transmission of a coded signal through a delaying medium and which permits a high signal-to-noise ratio and high accuracy. The received coded signal is applied to two correlators followed by a subtractor to form a discriminator circuit utilized to lock the frequency of a generator which provides two reference coded signal utilized respectively for correlation and to form an automatic tracking loop. The lag measurement is obtained by state-decoding of the transmission coded signal and of one of the reference coded signal and by pulse counting at a period sub-multiple of the bit period.