Abstract: A plurality of sensor arrays are mounted in a streamer cable. The sensors within each array are distributed over an elongated two-dimensional vertical plane. The seismic streamer cable is so constructed that its vertical dimension is substantially greater than its width and the top portion is relatively more buoyant in the water than the bottom portion. Because of that configuration the streamer cable resists vertical strumming and, when the sensor arrays are used in the differential mode, there is no orientation uncertainty.

Abstract: A system and method for forming a model of an underground geological formation is disclosed wherein a quantity of non-solid material of the type which solidifies at volumetric positions impinged upon by preselected incident energy as used. Memory means are provided which have uniquely addressable location for storing data indicative of the desired and actual material states at respective volumetric positions. Means are additionally for scanning the data and sequentially directing the energy at supported, non-blocking, volumetric positions in the medium volume.

Abstract: A first sweep signal consists of a plurality of waveforms having non-invariant fundamental periods exhibiting a monotonic frequency progression of at least one octave over the duration of the sweep. Each waveform may consist of an ordered set of asymmetrical pulses distributed within the period of the waveform in a prescribed sequence as a function of time. A second sweep signal is orthogonalized with respect to the first by time-reversing the distribution-sequence of the pulse set.

Abstract: Sweeps of seismic signals consisting of pulse trains having a predetermined number of pulses in which the periods or durations of the pulses are randomized and in which the wave shape and relative time displacements of the pulses in different trains provides substantially constant spectral level over a frequency range containing several octaves.

Abstract: A pressure gradient sensor is disclosed for optically sensing the direction and magnitude of an acoustic wave propagating through a fluid. Each sensor consists generally of at least three fiber-optic displacement sensors disposed within a circular array oriented perpendicular to the longitudinal axis of a streamer. Each sensor phase-modulates a coherent light signal indicative of the water pressure sensed outside the streamer. The output of the signals include a component due to transient pressure waves and a component due to hydrostatic pressure differences between the sensors.

Abstract: In a two-stage, time-division multiplexing method and apparatus, a plurality of sensors are disposed at equal intervals along a plurality of transmission channels. An interrogation signal is transmitted from a recording station to all of the sensors along each channel. Because of the spatial arrangement of each sensor along the telemetric system and different propagation path lengths along each channel, the output signals from the sensors are time-division multiplexed along each channel. The multiplexed signals along each channel are time-division multiplexed a second time upon arrival at the recording station where the signals from each channel are interleaved with each other.

Abstract: An optical telemetric system for use in a borehole consists of a bidirectional optical fiber to which are coupled a plurality of acousto-optical seismic sensors. The sensors consist of an optical cavity that becomes resonant at certain wavelengths depending upon parameters of cavity length and index of refraction. Those parameters are capable of being modified on the basis of static and dynamic pressure differences within the borehole. A swept-wavelength laser chirp pulse is launched into the bidirectional optical fiber. The static pressure at each sensor establishes a resonant wavelength that serves as a carrier signal. Dynamic pressure changes due to seismic waves, modulate the carrier signal. The modulated carrier signals from each sensor are reradiated through the bidirectional optical fiber in a wavelength-division multiplexed format. The multiplexed signals are received by and demultiplexed by a suitable signal receiving apparatus.

Abstract: A seismic data recording system includes a central station and a plurality of remote seismic data recording units that are deployed within a desired region relative to the central station. The differential locations of the remote recording units relative to the central station are determined by receiving and recording electromagnetic positioning signals at the central station. A portion of the electromagnetic positioning signals is concurrently received and recorded at the respective remote recording units. The portion of the positioning signals recorded at each remote recording unit is combined with the recorded positioning signals from the central station to determine the required differential locations.

Abstract: A method for maintaining a substantially constant tension on a towed seismic cable, wherein the instantaneous towing force and the instantaneous cable displacement relative to a fixed shipboard reference are continously measured and sampled. A microprocessor associated with a servo controlled capstan device, uses those measurements to pay out cable or to retrieve cable in response to an increase or decrease in the instantaneous towing force. The microprocessor also tries to minimize the average cable displacement.

Abstract: A quantity of a solution of a long-chain polymer is injected into the water around an air gun. The resulting dilute solution of the long-chain polymer tends to reduce turbulence surrounding the air bubble that is created when the gun is fired.

Abstract: A hydrophone streamer that includes several arrays of optical fiber pressure sensors. Each array consists of at least three sensors symmetrically disposed around the inside of the streamer skin to form a vertically-disposed array. Each sensor modulates a coherent light beam in accordance with the instantaneous ambient water pressure. The output signals of the sensors include an AC component due to seismic waves and a DC component due to hydrostatic pressure difference between the sensors of an array. Means are provided to resolve the AC and DC components to determine the arrival direction of the received seismic waves.

Abstract: Sweeps of seismic signals consisting of pulse trains having a predetermined number of pulses in which the periods or durations of the pulses are randomized and in which the wave shape and relative time displacements of the pulses in different trains provides substantially constant spectral level over a frequency range containing several octaves even though the durations of the pulses correspond to a frequency range not exceeding an octave during the sweep are transmitted through the medium being explored such as an earth formation to receptors such as geophones or hydrophones. Groups of signals contained in less than the entire length of the sweep which are transmitted and which are received can be cross correlated to vary the effective duration of the sweep. The cross correlation output of successively occurring sweeps may be stacked to reduce the side lobe amplitude of the cross correlation outputs from each sweep, from which outputs seismograms may be constructed.

Abstract: A dual-transducer accelerometer, having a liquid inertia mass is disclosed. Each transducer consists of a ceramic PZT piezo-electric wafer glued to a flexible substrate. Certain characteristics of sensitivity and capacitance of one transducer can be matched to similar characteristics of an arbitrarily-selected standard by laser-trimming the ceramic wafer.

Abstract: A seismic cable assembly has approximately 500 equally spaced elemental sensor units to receive seismic signals generated in the earth by a seismic impulse generator or "shot". The sensor units each include 3 hydrophones or geophones spaced about 6 feet apart, for a sensor unit length of about 12 feet, to receive seismic signals up to several hundred hertz. Signals representing seismic waves received at each of these 500 units are transmitted from the cable, to a central control and recording unit, mounted in a vehicle such as a towing ship. Connected to the cable will be one or more array-forming systems for processing seismic data from the sensor to synthesize various direction-sensitive hydrophone arrays located along the seismic cable.

Abstract: A seismic data acquisition system provides seismic signal data samples in multiplexed channel sequential order during a recording cycle. The multiplexed data samples from a recording cycle are demultiplexed by storing the data samples in consecutive order in a memory, having addressable locations, in addressed locations separated by a first desired address increment. The data samples are then extracted from addressed locations that are separated by a second desired address increment. Substantially concurrently, data samples from a subsequent recording cycle are stored in the memory locations vacated by the previously extracted data samples. The data samples from the subsequent recording cycle are demultiplexed by extracting stored data samples from memory locations that are separated by a third desired increment. The above steps are repeated for additional recording cycles, using a different address increment for each extraction step.

Abstract: The seismic source consists of a tank for containing a volume of water. The tank is held in firm contact with the ground by suitable weighting means. The tank wall that contacts the ground is thinner than the other walls. The volume of water in the tank is pressurized to one to three atmospheres. An imploder is mounted in the tank, submerged in the water. When the imploder is fired, reducing the tank pressure abruptly, a negative pressure pulse is generated in the water. The negative pressure pulse is transmitted from the water, through the thin ground-contacting wall, to the ground, producing an acoustic pulse whose first motion is one of rarefaction.

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: A seismic exploration system includes a recording vehicle having a seismic cable connected thereto and one or more vibrator units. The seismic sensor cable includes at least one unterminated conductor. Operation of the vibrator units is programmed by transmitting, at very low frequency (VLF), a frequency-modulated, coded control-signal from the recording vehicle into the unterminated conductor. The conductor, acting as a VLF antenna, radiates a weak electrostatic E-field. A ferrite-core loop antenna on the vibrator unit detects the coded control signal, thereby to initiate the required vibrator operation. If desired, a reproduction of the seismic signal generated by the vibrator can be transmitted back to the recording truck over the same VLF radio link.

Abstract: A seismic exploration system for use on ice-covered waters is disclosed. The system comprises a housing which contains equipment such as an engine, a compressor, means for boring holes in the ice, and acoustic signal generating means that can be lowered into the water through holes in the ice. The housing is sufficiently lightweight that it easily can be transported from one location to another by helicopter or other aircraft. The heat generated by the engine is sufficient to provide a comfortable working environment for personnel within said housing and helps prevent freezing of equipment located within said housing.

Abstract: A single time-multiplexed channel for telemetry of seismic data from a plurality of remote, spaced-apart sensors to a central recording device. All of the sensors are identical and interchangeable. A unique polling signal is transmitted over a telemetry link to each sensor. Upon receipt of the polling signal, each sensor in turn transmits its accumulated data over the telemetry link to a recording device. The time-delay due to polling-signal propagation between successive sensors provides a time window during which each sensor can transmit data.