Abstract: A method for optimizing the acoustic signal-to-noise ratio during a useful maximal-length recording cycle within the time frame of a minimal-length recording episode. To implement the method, during an intermittent-tow seismic operation, the noise level due to cable manipulation during an entire recording episode is monitored. A quiet-window of a desired length is established by adjusting the length of the interval during which the seismic cable is at rest. The initiation of a recording cycle is adjusted relative to the quiet window to take maximum advantage of the quiet period.

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: Selected sections of a seismic streamer cable are provided with an acoustically-triggered compressed gas supply. The acoustic triggering devices associated with each compressed gas supply may be individually addressed by a coded signal. In the event that the streamer cable is severed, the gas supplies of the severed sections of the streamer are used to inflate the jackets of those severed sections so that they will float to the water surface for salvage.

Abstract: In accordance with an embodiment of this invention, voltages are received from the pilot valve torque motor, the main servo valve and the actuator indicating the value of the torque motor current, spool position and actuator displacement. The received voltages are compared to a preselected threshold value. When one or more of the voltages exceed a threshold value, an attenuator control voltage is generated. An attenuator circuit is coupled between the reference driver signal generator and the DC servo amplifier. The attenuator control voltage, if present, is applied to the attenuator circuit and scales down the reference driver signal as a function of the error signal level thereby to limit the torque motor current and consequently the displacements of the main servo valve spool and actuator shaft.

Abstract: A pulse is applied sequentially to each geophone input line to the stator of a CDP switch. A pulse detector is connected to the first output line of the CDP Switch cursor. A counter counts the number of pulses applied to inactive input lines before a pulse is detected by the pulse detector. The pulse count is the geophone group number of the first active geophone group.

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 streamer cable, composed of a plurality of cable sections includes a common transmission line and an internally mounted inductive element in each section. The inductive elements are coupled in parallel to the common transmission line. A plurality of depth transducers, each associated with an inductive pickup, are secured externally to the streamer cable at desired intervals, adjacent to one of the internal inductive elements. A control signal is periodically transmitted through the transmission line and is received, by inductive coupling, at each transducer after a selected delay. In response to the delayed control signal, the transducers inductively launch a depth-proportional signal into the transmission line for reception by a depth readout device.

Abstract: A hydraulically-powered yo-yo reel for handling a marine seismic cable in shallow water. At the beginning of a recording episode, a partially reeled-in seismic cable is released to drift to a standstill behind a ship. Data are recorded. The cable is then accelerated to match the ships's velocity. Following the initial acceleration, the cable is superaccelerated as it is partially reeled in. A microprocessor adjusts a dwell time between recording episodes to compensate for small variations in the ship's velocity.

Abstract: The resistive sensor consists of a pair of electrodes separated by an impervious insulating material. The sensor is mounted adjacent to an exhaust port of an airgun, in the path of the air blast that results when the gun is fired. When the air gun is submerged and not activated, the surrounding water creates a low-resistance path between the electrodes. When the gun is fired, the air blast blows the water away from the electrodes and the resistance between them abruptly increases substantially. A bridge circuit detects the instant of resistance change and generates an electrical transient to mark the time that the gun fired.

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: A two-axle, four-wheel-drive vehicle has separate hydraulic drive systems to drive the front and rear pairs of traction wheels. Each drive system includes a hydraulic motor that is powered by its own variable displacement pump. The torque developed by the motors, and the hydrostatic drive pressure, depend on the volume of fluid flow from the pumps. Under certain conditions, the hydrostatic drive pressure to the two motors becomes unbalanced. A torque equalizer valve is interconnected between the two hydraulic drive systems. When the equalizer valve senses a hydrostatic drive pressure difference between the two drive systems, it readjusts the displacement of the pump having the higher pressure by lowering the hydrostatic pilot pressure to restore the balance of hydrostatic drive pressures.

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: 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: The compression portion of an instantaneous companding (compressing-expanding) system includes at least two and preferably four "bi-gain" amplifiers connected in cascade. Each bi-gain amplifier normally has a low-gain state and can be switched to a discrete high-gain state. A discrete reference voltage is provided to compare with the output of each amplifier. The amplifiers are initially switched to their low-gain states and the reference voltage corresponding to the first amplifier is selected. A comparator means makes a comparison between the system's output voltage and the selected reference voltage. The control means switches the first amplifier to its high-gain state or holds it in the low-gain state depending on the result of the comparison. By utilizing a different variable reference voltage and bi-gain amplifiers with two different amplification factors, the number of amplifiers and comparisons is significantly reduced.

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: 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: This invention relates to synchronizing switching systems for modulation of light spectrum frequencies, and a cathode-ray tube apparatus for exposing and simultaneously at electronic speed synchronizing such frequencies onto celluloid light sensitive photographic film. A method for so synchronizing modulating light spectrum frequencies, and for exposing such frequencies on such light sensitive film using a cathode-ray tube light source is related.

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.