Abstract: A fiber optic acoustic sensor system including an optical conductor having low reflectivity mirrors is provided. Optical sensors are provided by sections of the optical conductor bounded by pairs of the low reflectivity mirrors. Pulses of light are injected into the optical conductor and reflected by the low reflectivity mirrors. The reflected pulses of light are processed using a compensating interferometer to generate interference patterns representative of the environmental conditions acting upon the optical conductor.

Abstract: A marine seismic fiber optic acoustic sensor system having internal mirrors with a low reflectivity written into the fiber to form a series of continuous, linear sensors incorporated in a single fiber, each sensor bounded by a pair of internal mirrors. A pulsed laser provides optical signals to the fiber at a pulse width less than twice the travel time to assure that there will be no phase or frequency modulation of signals returned from the sensors and reflected optical energy is returned through the same fiber to an optical coupler where it is input to a compensating interferometer to produce interference signals which are then time division multiplexed to produce signals corresponding to acoustic signals received by each mirror bound sensor. Calibration to remove local temperature effects is provided by using a desensitized reference fiber with internal mirrors identical to the sensitized fiber, by a piezoelectric stretcher built into the fiber or any other conventional calibration technique.

Abstract: The invention is a seismic acquisition system for communicating seismic sensor signals to a recording unit, including a control unit and analog-to-digital conveyer units connected to the control unit. The conveyer units each include integral interconnecting cables having an hermaphroditic connector at each end, analog seismic sensor inputs and signal processing circuitry disposed within a watertight housing forming part of the cables. The circuitry includes analog-to-digital conveyers connected to the analog inputs, a buffer for digitized signals transmitted to one converter unit from other converter units interconnected to the conveyer unit opposite to the control unit connection, a digital transceiver for retransmission of digitized sensor signals and the buffered signals at a first data rate to the control unit. The control unit includes a second buffer for signals from the conveyer unit and for signals retransmitted from other control units serially codected to the control unit.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: A method and apparatus for detecting the instant on explosive is detonated by way of an optical signal. A length of optical fiber has one end wrapped around or positioned near the explosive with the other end coupled to a remote recorder. The end of the fiber at the explosive has been cleaved so as to internally reflect an optical signal propagating therein. A beam of radiation is launched into the fiber at the record where it is reflected from the distal end and redirected back to the recorder where it is detected. Detonation of the explosive destroys the reflective end of the optical fiber causing the radiation to leak from the broken fiber end. The instant the recorder does not receive the reflected radiation is the instant of the explosive detonated.