GB1465306A - Transmission line seismic communication system - Google Patents

Abstract

1465306 Seismic exploration GLOBE UNIVERSAL SCIENCES Inc 30 Oct 1974 [5 Nov 1973] 46946/74 Heading G1G [Also in Division G4] In a seismic communication system, a central station sends a strobe burst over a continuous twinlead transmission line to a plurality of remote stations all of which respond by subsequently inserting digitized seismic data on to the line at successive time slot intervals. At each remote station, detection of a pilot signal switches on the power to the station, power being switched off again on detection of an inordinate gap between strobe bursts. The strobe burst is a pseudo-random bit pattern in bi-phase-mark form which is decoded from this form and recognized in each remote station as it goes down the line, to synchronize the station by selecting the next appropriate output signal of a crystal clock in the station and starting a time slot counter, the station being controlled so that outputs from three geophones at the station are digitized in turn into gain and mantissa portions which are stored together with header information, overall gain, in one of two memories, used alternatively, encoded into Miller code and applied to the line after the strobe burst and any such data from preceding stations on the line. Parity bits are also sent. The remote stations are arranged in a linear array, the central station being alongside one of them to divide the array into two sections which use respective transmission lines, the central station having two transmitters and two receivers. Shot points are provided near at least some of the remote stations and when the active shot point and active remote stations are to be advanced along the sequence of points and stations, "roll along", a calculator in the central station, under operator control, advances the station number and time slot number assignments. The data from the remote stations is supplied via a processor to one of two memories, used alternately, as the other memory is read out via a re-multi-plexer and recorded on tape. The tape can be played back via a D/A converter and de-multi-plexer to a camera. The tape recorder can be by-passed. A display is provided of the system. The shots can be triggered from the central station by radio or via transmission lines, perhaps by a coded signal.