Patent GB-1097963-A (GB)
Title: Hybrid data-processing system
IPC: G01V1/28
Filed: 1965-04-01
Abstract: 1,097,963. Seismic prospecting. MOBIL OIL CORPORATION. April 1, 1965 [April 1, 1964; Dec. 29, 1964], No. 13858/65. Heading H4D. In a seismic data processing system, analogue and digital processors are used concurrently. In the embodiment of Fig. 1, seismic data recorded in analogue form on a multi-channel magnetic drum 1 is converted to digital form in A/D converter 12 by sampling the reproduced analogue signals at selected intervals controlled by " strobe " pulses applied to converter 12 from a control unit 4 which also synchronizes the operation of converter 12 with the playback from drum 1. The output of converter 12 is stored in registers of a digital computer 13. For eliminating multiple and ghost reflections from a seismogram by a feedback technique, computer 13 is programmed to act as a lownoise multi-channel electronic delay line and as such applies different delays to the digital samples of a seismic trace. The differently delayed samples are reconverted to analogue form by D/A converter 17 (at a rate controlled by " readout " pulses from control unit 4), adjusted in polarity and amplitude by amplifiers 18 and summed in adder 23 to provide a cancellation signal which is fed back via adder 22 to the input of A/D converter 12. The outputs of amplifiers 18 are monitored on a recording oscillograph 21 and on multi-channel oscilloscopes 19, 20 enabling the delays applied by computer 13 and the phase and amplitude of the cancellation signal to be adjusted for optimum elimination of multiple and ghost reflections. The processed seismic trace is recorded on a magnetic drum 2 and the output of computer 13 is recorded in digital form by a magnetic tape unit 15 and paper tape punch 16. A selected portion of an analogue seismic trace may be processed by initiating the analogue-todigital conversion by converter 12 in known time relation (controlled by unit 4) with the start (" time-break ") of the trace. Details of the logic, timing and switching circuitry of the control unit 4 are given (Figs. 1a, 2, 3, 4, 5a, 5b, none shown). In a modification (Fig. 8) for the rapid auto-correlation or cross-correlation of seismic traces, two functions to be correlated are stored in digital form in a computer (801). The two functions are time-compressed then read out from computer (801), converted to analogue form by respective D/A converters (802) and (803), and multiplied together by analogue multiplier (804). The product is integrated by analogue integrator (805), converted to digital form by A/D converter (807) and stored in computer (801) as one point on the correlation function. Successive points on the correlation function are derived by introducing successive time shifts between the two digitized functions stored in computer (801) and repeating the time-compression, D/A conversion, multiplication, integration and A/D conversion steps for each time shift. In an arrangement for the direct recording of the output of a geophone array in digital form on a magnetic tape (Fig. 6), the output of each geophone in turn is converted to digital form by a converter (610) and read into a buffer register (611) from which it is transferred to a digital magnetic tape unit (612). For monitoring the data recorded, the digital samples from buffer register (611) are re-converted to analogue form by D/A converter (613) and applied to recording oscillograph (616). The sequential sampling of the geophone signals and the operation of register (611) are synchronized by control unit (608), details of which are given (Fig. 7, not shown).