Patent GB-493704-A (GB)
Title: An improved system and apparatus for detecting by radiation-sensitive devices the presence and/or position of objects, more especially invisible or obscured distant objects
IPC: G01S7/282
Filed: 1937-04-09
Abstract: 493,704. Photo - electric directional range-finding; discharging guns. MOBSBY, E. C. H., and NICHOLSON, G. April 9, 1937, No. 10165. [Class 40 (iii)] [Also in Group XXI] Objects are detected and their positions determined by a means for projecting a beam of electromagnetic waves within the infrared, visible and ultra-violet bands, towards the object, a receiver for those rays reflected by the object and means for causing fluctuations in the rays reaching the receiver so that they may be converted into suitable currents for detection, such as of audio frequency. A source of electromagnetic waves, such as an arc lamp A<1>, is situated at the focus of a parabolic reflector A of searchlight type which reflects the waves in the form of a parallel beam A<2> through a filter A<3> and a shutter G, either of the rotating or slat type, towards the object E. Reflected rays E<1> are focused by a reflector B on a suitable sensitive device B<1>. Periodic fluctuations of any desired frequency are produced in the beam by the shutter G, and the corresponding variations in the current passed by the sensitive device B<1> are detected by headphones B<3> or by the operation of a relay F to light a lamp F<2>. The distance of an object may be determined by placing before the transmitter and receiver identical, synchronously operated shutters and increasing their rate of operation until complete occultation of the reflected beam takes place. The distance is calculated from the known speed of operation and the speed or propagation of the waves or is read from an appropriately calibrated meter. Alternatively the time taken for the rays to pass from the transmitter and back to the receiver is determined by measuring the phase difference between the transmitted and reflected rays by means of oscillographs. A further method is by placing the transmitter a known distance from the receiver and by measuring their relative angular bearings. These systems of range finding may be applied to depth sounding at sea but in this case infra-red rays would be unsuitable. This application may be adapted to indicate shallow water by projecting a beam downwardly from the bow of a ship and mounting the receiver at the stern in a predetermined fixed position so that it receives rays reflected from the sea bottom when the ship enters water of a certain depth and so causes a warning device to be operated. The response of the receiver to the rays reflected from an object may further be applied to the counting of objects or persons passing a certain point or to the automatic firing of a gun, in which latter case the beam is projected in the same direction as the gun and the presence of an object in the path of the beam causes the firing of the gun by reflection of the rays. The system may be used on aircraft to cause automatic firing of a machine gun when it is trained on another aircraft. In such cases the gun may be controlled by an alternating current relay connected to an amplifier the input of which is controlled by the sensitive cell of the receiver.