Patent GB-990654-A (GB)
Title: Multifunction correlation
IPC: G06G7/19
Filed: 1962-10-23
Abstract: 990, 654. Multifunction correlation. ATLANTIC REFINING CO. Oct. 23, 1962 [Nov. 1, 1961], No. 40044/62. Heading G1U. [Also in Division G5] In a method of securing useful information from three or more signal functions, where each of the functions contains a signal of interest together with unwanted components, the steps taken are as follows: (a) The functions are separately received. (b) A predetermined constant is added to all of the functions to produce modified functions. (c) A portion of one of the modified functions is selected. (d) An equivalent length portion from each of the remainder of the modified functions is simultaneously multiplied with the selected portion and this product is integrated over the length of the selected portion as the equivalent length portions are displaced in an arbitrarily related manner, and (e) Values of the integral are displayed to indicate the magnitude of multi-signal correlation. The invention may particularly be used in the interpretation of seismic records. These may be presented in the form of variable density photographic records, and in the described optical correlator (Fig. 3) these records pass through a viewer 7 and are arranged in a film feeding system 21, being attached at one end to an arm 27, at the other to the weights 35. The radii of the film guides 29 are related by integral multiples of the smallest guide so that linearly related film displacements may be obtained. In operation the seismic signals used, which may be obtained from a linear geophone spread, are corrected for fixed and variable errors before being recorded on separate variable density films. The films are placed in the correlator with the guide arm 27 set to a 45 degrees angle with the horizontal and with the films correctly aligned in accordance with timing marks upon them. With the viewer 7 in the desired correlating position, light from the lamp 9 passes through the films and is received by a photomultiplier tube 11, which produces an output voltage proportional to the light intensity received. This output is passed to a balancing circuit 53 which compensates for the D.C. component produced by the photomultiplier dark current, and then to the Y axis of an X-Y plotter 23. The X axis voltage for the plotter is developed from the linear potentiometer 39 which is coupled to the arm 27. To produce a correlogram from the various records it is necessary to enter delays into their relative time positions, and this is achieved by operating the drive motor 25 so as to move the arm 27, thus causing the record films to be displaced with respect to one another in a predetermined manner. At the end of sweeps in each direction the arm actuates the switches 68 and 69 which are arranged to cause the motor to reverse, and a correlogram indicating transmitted intensity against delay (Fig. 4) will be traced out on the plotter. Correlograms are taken with the viewer 7 in different positions and the differing delay times for maximum correlation may be used to determine, for example, subsurface dip angles and the like. The method may alternatively be practised using the electrical system of Fig. 6. Three functions to be correlated are fed through magnetic heads 107 to a rotating magnetic drum 71 and are picked up at a later time through heads 109. These heads may be moved in any arbitrary manner about the drum, so that varying delays may be introduced. The functions related to the delay times are then passed through summing networks to the amplifiers 73, 75 or 77. The summing networks also have a constant voltage from a source 111 and potentiometer 113 applied thereto so that functions modified by the addition of a predetermined constant are derived from the amplifiers. These functions are passed to the multipliers 91, 93 and finally to the integrating unit 99, so that a correlation function may be traced out on the plotter 101. The periods of integration are controlled by means of a timing track 105 on the drum, which provides a synchronizing signal to the timing and control circuit 95. A mathematical discussion is included in the Specification. Specification 914,359 and U.S.A.Specification 2,839,149 are referred to.