Western Geophysical Company of America

Litton Resources Systems, Inc.

Western Atlas International, Inc.

Lee E Siems

Paul M Morgan

Carl H Savit

James A Porter, Jr

Loring C Chien

Marvin K Amerine

William P Vorheier

In a marine seismic data acquisition system, a plurality of seismic data transmission paths are utilized to conduct seismic data to a central recording unit from seismic data acquisition modules positioned along the length of cable. Signals from a plurality of data acquisition modules are applied to each of the transmission paths. Data acquisition modules which apply seismic signals to a given transmission path may be spaced and substantially uniform distances along the length of the cable and may be interspersed with data acquisition modules which apply seismic data to each of the other transmission paths. The operation of the data acquisition modules is synchronized by means of a signal transmitted continually from a central recording unit. Each section of the cable includes a plurality of remote units distributed along the cable section for detecting seismic signal. Each section includes a data acquisition module which receives command signals from a central recording unit and which receives seismic data signals from the remote units and transmits seismic data signals to the central recording unit.

Multiple transmission path seismic telemetering system

An optical telemetric system for use in seismic exploration consists generally of a recorder, a plurality of transceivers, and a like number of cable sections interconnecting each transceiver in parallel with others and the recording unit. A fiber optic transmission channel is provided within each cable section and is interconnected by an optic-fiber delay loop within each transceiver, thus providing a contiguous, optically-continuous data and control channel. Within each transceiver, a logic circuit and associated data acquisition unit is optically coupled to the data and control channel so as to bidirectionally receive signals from, and transmit signals to the recorder. The logic circuit of each transceiver also is able to measure the strength of a received signal propagating in the data and control channel, and if necessary, augments the signal in the original propagation direction. An optical direction sensing circuit is interfaced with each logic circuit for electronically facing each transceiver towards the recorder. The instant invention thus reduces the effect of the series reliability law upon regenerated data.

Optical telemetric transceiver

A data telemetric system consists of a pair of optical fibers, each having an associated electrically conductive member. One of the fibers is a reference fiber and the other fiber constitutes a data transmission fiber. A light beam, from a source such as a laser, is launched from one end into both fibers. A signal transfer sensor is non-invasively coupled to the data fiber and applies forces to that fiber that are related to data signals thereby to modulate the light beam therein. A comparator at the other end of the pair of fibers compares variations in a characteristic of the modulated beam with corresponding characteristics of the reference beam to decipher the transmitted information. Means are provided in the signal transfer sensor for inductively sensing control and power signals transmitted through the electrically conductive member.

Seismic data telemetric system

A decentralized seismic data recording system includes a central station and a plurality of remote seismic recording units that are incommunicado with the central station during a normal recording operation. A master clock is provided in the central station. A local clock is provided in each remote recording unit. At the beginning of a work period, the local clocks are synchronized with the master clock. Thereafter, a plurality of seismic data recordings are made. At the end of a work period, the time difference due to tuning drift between the master clock and each respective local clock is ascertained and is recorded. The time difference is linearly prorated over the recordings made during the work period, thereby synchronizing the time base of each seismic data recording with the master clock. Provision is made to validate each seismic data recording to prevent accidental recording of false data in event of a misfire or a non-fire of the seismic source.

Seismic data recording method and apparatus

The telemetric system consists of a large number of identical cable sections laid over the ground end-to-end, in a long array or 'spread'. The cables have a number of external connectors along their length for connecting geophone groups. The cables are electrically and physically interconnected by a like number of data transceiver modules. The data transceiver modules contain circuitry to receive and process data from the various geophone groups. A recording and control unit is connected to the spread at some convenient accessible location. The recording and control unit transmits control signals to the respective data transceiver modules. In response to the control signals, the respective modules transmit digital seismic signals, back to the recording and control unit. The cable sections and data transceiver modules are not polarized; that is, it is immaterial which end of a cable section is plugged into which side of a transceiver module. The same telemetric link that is used to transmit command and interrogation pulses to the respective transceiver modules is also used to receive digital data words from the respective modules. Accordingly, a direction sense circuit in each module determines the direction of any given module with respect to the recording unit and orders the digital logic contained within the module to electrically 'face' the recording unit.

Seismic telemetric system for land operations

The seismic system includes a seismic sensor cable assembly having 50 cable sections and much of the seismic data processing electronics decentralized into the cable structure itself. The cable assembly is coupled to a central station mounted in a recording vehicle. The central station includes recording circuitry and apparatus to receive, process and record digital data words from a data link in the cable assembly and circuitry for transmitting control signals into an interrogation link in the cable assembly. The electrical output of each sensor unit constitutes a separate input channel. The cable sections are spaced apart and interconnected by small-diameter, cylindrical connector modules which contain a transceiver unit for processing the signals from ten sensor units in an associated cable section. Contained within each transceiver unit is a multiplexer having a plurality of filtered input channels coupled respectively to the elemental sensor units, and an output. In response to a first interrogation pulse transmitted through the interrogation link from the central station unit, the multiplexer advances to a selected input channel to acquire a first analog data sample. A second interrogation pulse sequences the respective multiplexers in all 50 modules to select a second channel for sampling and digitizing to provide digital data-words for the respective second channels. The self clocking phase-encoded data words transmitted from the respective transceiver associated with each cable section are ordered in accordance with the propagation delay time of the interrogation link between the central station and the respective transceiver units. Self clocking data words from corresponding channels within the respective transceiver units are ordered in accordance with the channel-select sequence during a scan cycle.

Decentralized seismic data processing system

It is a purpose of this invention to dispose a large number, such as 500, of elemental seismic sensor units over the earth's surface in a desired pattern. The sensors are arranged preferably in a linear pattern, at increasing distances, remotely with respect to a central station. Each elemental seismic sensor unit comprises a short subarray consisting of three seismic detectors, electrically interconnected. Each elemental sensor unit is a separate source of seismic signals. At regular intervals the analog seismic signals from the elemental sensor units are sampled in sequence and are digitized as a 20-bit binary number. The binary numbers are representative of the analog signal levels. The binary numbers are encoded in a self-clocking, return-to-zero pulse code as digital data words. The data words from the respective elemental sensor units are time-delay multiplexed into a wide band transmission channel for transmission to the central station in a constant current mode. Spaced along the transmission link are a series of transceiver units to each of which several separate sensor units are connected. The transceiver units are connected in series and include a repeater network which receives and retransmits data words from down-link transceivers, as well as data words derived from each of the locally-connected sensor units. Each repeater network also includes a word detection circuit, a local clock, and synchronizing circuitry. In the central station, the respective data words are stored as a matrix, in a core memory in sequential order. A formatter extracts from the core memory, data words that originated from selected groups of the elemental subarrays. The data words are combined to form new composite data words representative of seismic signals originating from desired longer arrays. The composite data words are transferred to a recording medium, such as a magnetic tape, for storage or future use.

Multichannel seismic telemeter system and array former

A multi-channel analog system comprises a plurality of channels each being adapted to receive analog signals from a signal source such as a seismic sensor. A multiplexer multiplexes the analog channels prior to converting the channels' signals into digital numbers. Each channel has a DC blocking capacitor connected to one terminal of a normally-open multiplexer switch; the other terminal of the switch is coupled to a multiplexer bus. In accordance with this invention, the bus is connected to a common resistor. Control means consecutively close the multiplexer switches so that the capacitor whose switch has been closed forms a high-pass filter with the common resistor. The resistor is preferably connected as the input resistor to an operational amplifier. The capacitors, the multiplexer, and the common resistor form a multiplexer-commutated high-pass filter which is particularly adapted for multi-channel seismic systems.

Multiplexer commutated high pass filter

A plurality of data acquisition and transceiver units are connected in series to a central signal processor through a common telemeter link. The telemeter link includes a data channel, an interrogation channel and a control channel. The signal propagation velocity through the control channel may, for example, be greater than the signal propagation velocity through the interrogation channel. The central signal processor sends an interrogation signal through the interrogation channel to the data acquisition units. After a selected delay, a control pulse is transmitted. The delay between transmissions of the two signals is proportional to the differential travel time of the signals in the two channels. Accordingly the signal through the control channel will overtake and intercept the signal propagating through the interrogation channel, at a selected data acquisition unit. When any selected data acquisition unit receives a control signal through the control channel at the same time that it receives an interrogation signal through the interrogation channel, that unit is activated and a desired function is performed. The control signal is a square wave pulse having a width which is adjustable by integral multiples of the differential travel time. By adjusting the width and transmission-time delay of the control pulse, any selected subset of one or more consecutive units may be activated. Each data acquisition unit may have two or more input channels, which are connected in turn through common electronics to the data transmission channel by means of a channel selector or multiplexer. The interrogation signal may exist in one of two or more states. In the first state, in combination with a control pulse, the interrogation signal resets the multiplexer. In the second state, the interrogation signal advances the multiplexer to the next input channel in sequence.

Seismic data telemetering system

In a multi-channel multiplexed system, each signal-receiving input channel has a DC blocking capacitor. One of the input channels to the multiplexer is grounded making this channel a test channel. A signal-conditioner-and-amplifier network (SCAN) couples the multiplexer output to a utilization device. The spurious voltage developed across the capacitor in the test channel combined with the offset voltage across the SCAN will be substantially the same as each one of the spurious voltages developed across the capacitors in the other input channels in combination with the SCAN offset voltage. A sample-and-hold circuit consisting of a series capacitor and a normally ungrounded shunt switch is connected between the output of the SCAN and the input to the utilization device. Periodically, as during each scan cycle of the multiplexer, the capacitor in the sample-and-hold circuit will be charged to and hold a sample voltage having equal amplitude but opposite polarity to the spurious voltage developed across the test channel capacitor in combination with the SCAN.

Multiplexer offset removal circuit

A plurality of data acquisition units are connected to a central signal processor through a common telemeter link. The telemeter link includes a data channel, an interrogation channel and a control channel. The central signal processor sends an interrogation signal through the interrogation channel to the data acquisition units. As each data acquisition unit recognizes the interrogation signal, it transmits its acquired data back to the central signal processor through the data channel. Any selected data acquisition unit, when it receives a control signal through the control channel at the same time that it receives an interrogation signal through the interrogation channel, can be caused to perform a function different from all other units. The signal propagation velocity through the control channel is different from the signal propagation velocity through the interrogation channel. One of the two signals may be transmitted through the faster channel at a selected time later than the other of the two signals is transmitted through the slower channel. The selected time difference between the transmission of the two signals is proportional to the ratio of signal propagation delay difference between channels. Accordingly the signal through the faster channel will overtake and intercept the signal propagating through the slower channel, at the selected data acquisition unit. Each data acquisition unit may have two or more input channels. Each input channel is connected in turn to the data channel through a stepping switch or multiplexer. The interrogation signal may exist in one of two or more states. In the first state, the interrogation signal resets the multiplexer. In the second state, the interrogation signal advances the multiplexer to the next input channel in sequence.

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Houston, TX, United States of America

Lee E Siems