Abstract: A sweep generator is employed to generate a sweep to be used by a seismic vibrator device for generating a desired target output spectrum, wherein the frequency sweep is designed so as to comply with one or more constraints imposed by the seismic vibrator device and/or imposed by the environment in which the device is to be used. In one embodiment, a sweep generator determines a sweep for achieving a desired target output spectrum by a given seismic vibrator device in compliance with at least a pump flow constraint imposed by the seismic vibrator device. In another embodiment, a sweep generator determines a sweep for achieving a desired target output spectrum by a given seismic vibrator device in compliance with all of multiple operational constraints of the seismic vibrator device, such as both mass displacement and pump flow constraints. Environmental constraints may also be accounted for in certain embodiments.

Abstract: A sweep generator is employed to generate a sweep to be used by a seismic vibrator device for generating a desired target output spectrum, wherein the frequency sweep is designed so as to comply with one or more constraints imposed by the seismic vibrator device and/or imposed by the environment in which the device is to be used. In one embodiment, a sweep generator determines a sweep for achieving a desired target output spectrum by a given seismic vibrator device in compliance with at least a pump flow constraint imposed by the seismic vibrator device. In another embodiment, a sweep generator determines a sweep for achieving a desired target output spectrum by a given seismic vibrator device in compliance with all of multiple operational constraints of the seismic vibrator device, such as both mass displacement and pump flow constraints. Environmental constraints may also be accounted for in certain embodiments.

Abstract: A sweep generator is employed to generate a sweep to be used by a seismic vibrator device for generating a desired target output spectrum, wherein the frequency sweep is designed so as to comply with one or more constraints imposed by the seismic vibrator device and/or imposed by the environment in which the device is to be used. In one embodiment, a sweep generator determines a sweep for achieving a desired target output spectrum by a given seismic vibrator device in compliance with at least a pump flow constraint imposed by the seismic vibrator device. In another embodiment, a sweep generator determines a sweep for achieving a desired target output spectrum by a given seismic vibrator device in compliance with all of multiple operational constraints of the seismic vibrator device, such as both mass displacement and pump flow constraints. Environmental constraints may also be accounted for in certain embodiments.

Abstract: A method for the simultaneous operation of multiple seismic vibrators using unique modified pseudorandom sweeps and recovery of the transmission path response from each vibrator is disclosed. The vibrator sweeps are derived from pseudorandom binary sequences modified to be weakly correlated over a time window of interest, spectrally shaped and amplitude level compressed. Cross-correlation with each pilot signal is used to perform an initial separation of the composite received signal data set. Recordings of the motion of each vibrator are also cross-correlated with each pilot, windowed, and transformed to form a source cross-spectral density matrix in the frequency domain useful for source signature removal and for additional crosstalk-suppression between the separated records. After source signature removal in the frequency domain an inverse transform is applied to produce an estimate of each source-to-receiver earth response in the time domain.

Abstract: A speaker system is used in conjunction with a surface seismic source that may be vibratory or impulsive. A speaker system having one or more speakers produces a sound signal that propagates primarily through the air and is received by microphones near the seismic spread. A transfer function between the microphones and the geophones in the seismic spread is determined from the speaker signal and used to filter out the airborne noise produced by the surface seismic source. The source may include or more vibrators that may be operated in a predetermined phase-relationship. The noise-attenuated signals may then be processed to separate out the contributions of the individual sources. Another embodiment of the invention uses accelerometer measurements of the reaction mass or the base plate of the vibrators or combination of the two measurements to invert the noise-attenuated signals.

Abstract: A seismic acoustic signal source includes a hull that has a wetted surface in contact with a body of water. When underway, the draft of the hull is substantially zero. An acoustic signal generator is provided with a linear actuator that is resiliently mounted in the hull. The linear actuator is acoustically coupled to the hull bottom such that when the signal generator is activated, the hull radiates an acoustic wavefield into the water.

Abstract: A method of separating the effects of the earth response on vibratory energy from individual ones of multiple vibrators to geophones, in generating a seismic survey, is disclosed. According to the disclosed method, measurements of the actual vibrations generated at the source are made, in addition to the geophone measurements of the refracted and reflected vibrations, both over a number of frequency sweeps. The source and geophone vibrations are first transformed into frequency domain representations, by way of Discrete Fourier Transforms. An inverse matrix of the recorded frequency-domain source vibrations is then generated for each frequency. When the number of sweeps equals the number of vibrators, the inverse matrix is merely the multiplicative inverse of the source measurements; if the number of sweeps exceeds the number of vibrators, the inverse matrix is the generalized inverse of the original matrix.

Abstract: A method of separating the effects of the earth response on vibratory energy from individual ones of multiple vibrators to geophones, in generating a seismic survey, is disclosed. According to the disclosed method, measurements of the actual vibrations generated at the source are made, in addition to the geophone measurements of the refracted and reflected vibrations, both over a number of frequency sweeps. The source and geophone vibrations are first transformed into frequency domain representations, by way of Discrete Fourier Transforms. An inverse matrix of the recorded frequency-domain source vibrations is then generated for each frequency. When the number of sweeps equals the number of vibrators, the inverse matrix is merely the multiplicative inverse of the source measurements; if the number of sweeps exceeds the number of vibrators, the inverse matrix is the generalized inverse of the original matrix.

Abstract: A rotary servo valve includes a valve body having a longitudinal bore therethrough. A sleeve fits into the bore. The wall of the sleeve is perforated by two groups of port openings, each group includes a plurality of sets of radially-disposed ports. In each group, the central longitudinal axis of one set of ports is radially displaced from the central longitudinal axis of one other set of ports by a preselected angular displacement. At least a third set of ports in one group is in continuous fluid communication with a source of pressurized fluid; at least a third set of ports in the other group in continuous fluid communication with a return sump. A hollow rotary control member consists of two internal chambers. Each chamber includes a number of sets of apertures that are radially disposed around the walls of the chambers, spaced-apart by a preselected angular separation.

Abstract: A self-orienting vertically sensitive accelerometer is disclosed for measuring a vertical component of acceleration independently of the orientation of the accelerometer. The accelerometer of the present invention includes a spherical plastic shell having a plurality of perforations disposed therein and a thin film of metallic coated piezoelectric polymer bonded to the exterior thereof, forming a small diaphragm at each perforation. In response to acceleration a dynamic pressure is developed within a fluid mass partially filling the spherical plastic shell which creates a strain and resultant charge in each small diaphragm of piezoelectric polymer. The vast difference in density between the fluid mass and the air in the remaining volume of the spherical plastic shell permits the charge developed in each small diaphragm under fluid pressure to be attributed solely to the vertical component of acceleration applied to the fluid mass.

Abstract: A piezoelectric seismic vibrator is disclosed which utilizes a hydraulic system to amplify the longitudinal displacement which results from the application of a voltage to a stack of piezoelectric elements. In each disclosed embodiment of the present invention, a stack of piezoelectric elements is mounted so as to bear upon a power piston which in turn acts upon a high bulk modulus substantially incompressible body of fluid, such as mercury. A drive piston is provided having a cross-sectional area which is smaller than the area of the power piston and the pressure within the fluid system acts to amplify the longitudinal displacement of the piezoelectric elements. The movement of the drive piston is then coupled mechanically or fluidically to the earth to generate seismic waves therein. In one depicted embodiment of the present invention each stack of piezoelectric elements is disposed within a fluid filled chamber which is pressurized by means of communication with the borehole fluids.

Abstract: A self-orienting vertically sensitive accelerometer is disclosed for measuring a vertical component of acceleration independently of the orientation of the accelerometer. The accelerometer of the present invention includes a spherical plastic shell having a plurality of perforations disposed therein and a thin film of metallic coated piezoelectric polymer bonded to the exterior thereof, forming a small diaphragm at each perforation. In response to acceleration a dynamic pressure is developed within a fluid mass partially filling the spherical plastic shell which creates a strain and resultant charge in each small diaphragm of piezoelectric polymer. The vast difference in density between the fluid mass and the air in the remaining volume of the spherical plastic shell permits the charge developed in each small diaphragm under fluid pressure to be attributed solely to the vertical component of acceleration applied to the fluid mass.

Abstract: Air wave noise caused by a vibrating baseplate on a seismic vibrator is reduced or eliminated through active cancellation of sound. In active cancellation, the detection of acceleration of the baseplate is used to form a counterpart wave which is equal in amplitude but opposite in phase; a speaker produces an opposite air wave to cancel the baseplate air wave.

Abstract: Air wave noise caused by a vibrating baseplate on a seismic vibrator is reduced or eliminated through passive absorption of sound. In passive absorption, reduction of air wave noise is achieved by building a rigid, light-weight enclosure for the baseplate which remains isolated from the induced ground vibrations and nonresonant.

Abstract: A method of reducing horizontally propagating pressure waves in marine seismic exploration improves the signal-to-noise ratio at associated receivers and reduces interference at unassociated receivers. Marine vibrators are arranged into an array with a given separation between each vibrator, so that horizontally propagating pressure waves from the vibrators which generally traverse the array are out-of-phase at most frequencies of vibration. The amplitude output from each vibrator varies with the output frequency of each vibrator to maximize the cancellation of out-of-phase pressure waves along the array. A receiver, which usually includes a plurality of hydrophones disposed in a streamer, is spaced from the marine vibrators at a distance sufficient to establish the receiver as being in the far-field. The output of each of the marine vibrators is locked in phase and frequency with a known pilot signal so that downwardly propagating pressure waves are substantially unaffected.

Abstract: The disclosure relates to a seismic vibrator having an airbag isolator, a transducer for monitoring the instantaneous air pressure within the airbags, a summer to add the pressures within each air bag and a calibrated weighting network to convert the composite pressure for display as holdown weight on a meter and for comparing the measured holdown against a preset threshold that is used to enable or disable sweep generation or operation of an inducer. The system also includes structure for comparing the measured holdown against a preset threshold that is used as a feedback signal to the lift system and for providing a signal proportional to holdown weight to the sweep generator for use as a feedback signal to modify the amplitude of the force generated by the actuator.

Abstract: A sweep generator for a seismic source vibrator provides for any one of a variety of sweep signals governed by input parameters. Selected analytic functions may be entered which are solved to provide a plurality of sweep parameters. The sweep parameters may also be directly entered by the operator. The time and frequency sweep parameters (or time and amplitude) are then employed to generate polynomial coefficients for consecutive use in a polynomial equation. The polynomial equation is repeatedly solved to generate a series of instantaneous frequencies or instantaneous amplitudes which are applied to an analog wave synthesizer. The analog wave synthesizer then generates an approximation to the desired sweep signal for input to the hydraulic system of the vibrator.

Abstract: A method of reducing Rayleigh waves (ground roll) in land seismic exploration employs a unique combination of amplitude output from and spacing of the vibrator sources making up a land seismic exploration system. The velocity of the Rayleigh wave for the prospect to be explored is determined. At least one receiver is used and is spaced from the vibrator sources a distance sufficient to establish the receiver as being in the far-field. The output of each of the vibrator sources is locked in phase and frequency and known separations between the vibrator sources are maintained. The frequency is varied and the individual output amplitude of each vibrator source is varied at each frequency so that the resultant Rayleigh waves traverse the known separations resulting in out-of-phase Rayleigh waves between the sources.

Abstract: A vibrator seismic source has a sweep generator for providing a pilot signal and sensors for generating a feedback signal representative of the force imparted to the ground by the vibrator pad. Circuitry is incorporated for separating the fundamental signal from the feedback signal and for separating the distortion from the feedback signal. Means are provided for generating a control signal for controlling the action of the vibrator means. Included are means for reducing the amplitude of the pilot signal a designated amount, determined by the distortion, and means for algebraically summing the reduced amplitude pilot signal and the fundamental signal to provide an error signal. The error signal is input to a loop filter to perform real time correction of the control signal. The reduced amplitude pilot signal is input to means for adjusting the control signal for trends in the distortion.

Abstract: A self-tuning controller, for dynamic control of the servo valve and the actuator (mass, column, pad) of a seismic source vibrator, includes a state variable feedback network associated with a model reference for the servo valve and the actuator. The model references provide controllable states of the servo valve and actuator that would otherwise be inaccessible. The models run on-line and have the same inputs as the servo valve and the actuator. A Kalman filter provides a full order observer that compares accessible states between each model and the servo valve and actuator, and updates the model states in dependence on the difference.