Abstract: A method and apparatus for determining electromagnetically the locations of electrically conductive bodies beneath the surface of the ground, wherein a primary electromagnetic field is generated with the aid of a loop through which a sinusoidal alternating current is passed. The loop is placed at or above the level of the ground beneath which the locations of conductive bodies shall be determined. There are currents generated in the conductive bodies which, in turn, generate a secondary electromagnetic field. The values of the amplitude and phase of the magnetic component of the thus formed total electromagnetic field are measured with the aid of coils mounted inside a probe which is lowered to different depths in a borehole. The values of the primary field phase are measured continuously by at least one reference coil which is placed outside the probe, either above or beneath the surface of the ground, within the propagation area of the primary field.

Abstract: Terrain resistivity is mapped by collecting data as to the vertical magnetic field ratio along a survey line by VLF survey techniques, and precision integrating rather than differentiating the data obtained. The received VLF signal is demodulated and low-pass filtered in a manner such as to preserve the DC component of the demodulated signal, and is then digitized and spatially integrated to obtain pseudo-resistivity readings along the survey line.

Abstract: A tool for evaluating electrical properties of an earth formation surrounding a borehole while drilling the borehole is disclosed. The tool includes a housing for connecting upper and lower portions of a drillstring, a transmit antenna for generating electromagnetic waves at least two receiving antennas for receiving electromagnetic waves and magnetic elements associated with each of the antennas for electromagnetically coupling each of the antennas with the formation. The tool provides improved transmit efficiency and improved receiving sensitivity.

Abstract: A method and system for determining the depth of an electrically conductive body in a medium having a known conductivity and a known permeability. The method comprises the steps of generating a primary magnetic field having a time-varying field strength, and transmitting that primary magnetic field into the medium. The primary magnetic field induces an electric current in the conductive body, and this electric current generates a secondary magnetic field that also has a time-varying field strength and that propagates outward from the conductive body and through the medium. The method of this invention further includes the steps of sensing the strength of that secondary magnetic field, comparing the primary and secondary magnetic fields to measure the phase difference therebetween, and then calculating the depth of the conductive body in the medium from the detected phase difference.

Abstract: A method utilized with an underground conductor detection system for calibrating a downhole transmitter to compensate for detuning of the transmitter antenna by geologic formations. The method comprises sending a synchronization signal to the transmtter antenna, measuring the current flow through the transmitter antenna and adjusting the current to a constant level, and measuring the phase difference between the transmitter antenna current and the synchronization signal. A receiver transmitter is calibrated by sending a synchronization signal to a radiating antenna in the receiver that in turn sends a calibration signal to the receiver antenna that is directed over the entire signal pathway back to surface located signal processing equipment. Another method of underground conductor detection sends a surface wave to the downhole receier to cancel the effect of the surface wave modulation on a target wave being radiated by the underground detector.

Abstract: In a method and apparatus for searching a subsurface environment to detect he presence of a target therein, an electromagnetic field is emitted which comprises successive electromagnetic pulses of selected duty cycle, the time interval between pulses comprising a zero emission interval and a sampling interval, the sampling interval following the zero emission interval, and the polarity of the pulses of the emitted field alternating at a selected alternating frequency. The emitted field is projected into the environment from a selected location, and the electromagnetic field proximate to the selected location is sampled during each of the sampling intervals to provide a train of proximate field samples. The train of proximate field samples is spectrum analyzed to determine whether or not the field proximate to the selected location contains a component having a frequency which is equal to the alternating frequency.

Abstract: The present invention is used to cancel a narrow band noise of know frequency, such as 60 Hz noise generated by powerlines, in electromagnetic receiving equipment. A cancelling antenna is wrapped around the sensing antenna of the electromagnetic receiver equipment. The cancelling antenna is provided with an alternating current signal of the same frequency as the ambient powerline noise. The cancelling antenna produces an electromagnetic field that is 180 degrees out of phase and of equal amplitude to the ambient powerline noise, as measured by the sensing antenna. The alternating current is produced by a noise antenna, a phase-locked loop and an amplifier. The noise antenna receives the ambient powerline noise, the phase-locked loop locks onto and tracks the frequency of the noise, and the amplifier provides the necessary amplification.

Abstract: An apparatus and method for detecting vertically or horizontally oriented underground electrical conductors such as electrical wiring or rails in tunnels thin conducting ore veins surrounded by less conducting rock, or boreholes filled with conductive water or lined with a conductive casing. The apparatus includes a surface or downhole transmitter and a downhole receiver connected to a coherent frequency source unit by fiber optic cables. The source unit generates two phase synchronized frequency signals in the range of one hundred to three hundred kHz. The receiver includes a vertical or horizontal magnetic dipole antenna, e.g. a ferrite rod antenna, and the transmitter includes a vertical or horizontal magnetic dipole antenna in the downhole configuration or at least one long cable or loop antenna in the surface configuration.

Abstract: A method of electroseismic prospecting is disclosed for detecting either the presence of two immiscible fluids present in a porous subterranean formation or the presence of a high-permeability rock formation including a substantially aqueous phase therein. A seismic impact produces an acoustical wavefront that results in an enhanced electromagnetic signal when it encounters either types of the above-described formations. This resulting enhanced electromagnetic signal is detectable as an indication of a likely hydrocarbon deposit, thereby giving additional data information with conventional seismic data to the geophysical prospector.

Abstract: The present invention relates to a system for acquisition and separation of the effects of simultaneous sources of electromagnetic field. According to the invention the system comprises an array of n pick-ups (1a . . . 1e) connected to registration means (2), the minimum number n of pick-ups per array being equal to 2s+2, where s is equal to a number of simultaneous sources to be analysed.

Abstract: Multiple arrays of electric or magnetic transmitters and receivers are used in a borehole geophysical procedure to obtain a multiplicity of redundant data suitable for processing into a resistivity or induced polarization model of a subsurface region of the earth.

Abstract: Eddy current type metal detector for locating and distinguishing between different classes of metal objects, and geophysical apparatus for measuring various properties of soil and rock. A nonsinusoidal transmit voltage energizes a transmit coil which transmits a nonsinusoidal alternating magnetic field into the soil, rocks or metal objects to be located. Distortion of the magnetic field caused by the presence of these materials in the field induces corresponding voltage waveforms in a receive coil. The induced waveform is analyzed in order to deduce certain electrical properties of the materials, or in order to distinguish buried metal objects from the soil in which they are buried. The circuit which energizes the transmit coil returns energy from the collapse of the magnetic field to the power supply, minimizing the power consumption of the apparatus.

Abstract: Apparatus and method for detecting geological anomalies occuring in geological formations. The instrumentation comprises a medium frequency continuous wave narrowband FM transmitter and receiver pair. Two instrument configurations are downhole instruments for insertion into boreholes. Survey procedures are provided to detect anomalies through signal attenuation, path attenuation and signal phase shift. Continuity measurements at different depths in the drillholes provide data to determine the existence of anomalies. Tomographic techniques are employed to provide a visual image of the anomaly. Computer aided reconstruction techniques provide such visual images from the generated data.

Abstract: Method and apparatus determining the water saturation of a petroleum reservoir earth formation include transmitting electromagnetic energy in the earth formation from within a borehole traversing the earth formation and at least two frequencies within a preferred range of frequencies. The electromagnetic energy is received at two locations from the earth formation and within the borehole. The water saturation of the earth formation is derived from the received electromagnetic energy.

Abstract: Instrumentation and procedures for detecting geological anomalies occurring in layered coal formations. The instrumentation comprises a medium frequency continuous wave narrowband FM transmitter and receiver pair. Two instrument configurations are disclosed with one being a portable instrument for use within an existing mined area and another being a downhole instrument for insertion into boreholes in unmined areas. Survey procedures are provided to detect anomolies through signal attenuation, path attenuation and signal phase shift. Continuity measurements provide data to determine the existance of anomalies. Tomographic techniques are employed to provide a visual image of the anomaly. Computer aided reconstruction techniques provide such visual images from the generated data.

Abstract: A conductivity anomaly detection system uses a rotating superconducting met to generate a known source field and an integrated detection system rotating with the superconducting magnet to detect anomalies in the generated source field caused by nearby conducting targets. The superconducting magnet is rigidly mounted in a Dewar which is in turn mounted on a shaft. An orthogonal detection system also is rigidly mounted on or within the Dewar with the superconducting magnet. The second harmonic of the anomaly signal from a target is detected for signal processing.

Abstract: An apparatus for direct airborne electromagnetic prospecting of hydrocarbons by transmitting many primary electromagnetic fields and detecting any deviation of the primary electromagnetic fields due to secondary electromagnetic fields. The transmitting and detecting operations are carried out first over a known area, as a stage of system instruction, and then over an unknown area, as a stage of actual prospecting. A transmitting system, suspended vertically from a helicopter, is adapted to radiate electromagnetic fields of many different frequencies and many different orientations controlled automatically. A receiving system, suspended vertically from the transmitting system, is adapted to detect signals of three orthogonal components of electromagnetic deviations as a function of helicopter altitude, frequency, transmitter loop orientation and receiver antenna orientation.

Abstract: In a surface layer of a massif or in a control medium brought in contact with the massif an electromagnetic field is established, and series of amplitudes of the field magnetic component or series of other electromagnetic field parameters are periodically measured, the parameters being a function of the electromagnetic parameters of the medium being irradiated. The measurements are made in a circle of up to 5 m radius with a center in a profile point, whereafter the results of measurements made in different times are compared and the contemporary geodynamic movements are evaluated from the variation of a characteristic of an azimuth anisotropy of the electromagnetic parameter of the medium being irradiated. From the nature of the variations of the characteristic there is determined a type of rock deformation associated with the contemporary geodynamic movements, and from the speed of these variations there is determined the intensity of the contemporary geodynamic movements.

Abstract: Instrumentation and procedures for detecting geological anomalies occurring in layered coal formations. The instrumentation comprises a medium frequency continuous wave narrowband FM transmitter and receiver pair. Two instrument configurations are disclosed with one being a portable instrument for use within an existing mined area and another being a downhole instrument for insertion into boreholes in unmined areas. Survey procedures are provided to detect anomolies through signal attenuation, path attenuation and signal phase shift. Continuity measurements provide data to determine the existance of anomalies. Tomographic techniques are employed to provide a visual image of the anomaly. Computer aided reconstruction techniques provide such visual images from the generated data.

Abstract: A frequency domain geophysical electromagnetic surveying system is provided in which intermittent primary fields having sharp terminations are generated in a cycle having a fundamental frequency by a transmitter, and a receiver includes a gate passing only secondary signals received during interruptions of the primary field, the gated signal being applied to filters tuned to harmonics of the predetermined frequency. The filter outputs are synchronously demodulated to provide signals corresponding to at least the in-phase component of the secondary signal at the fundamental frequency, and preferably in-phase and quadrature components at at least two harmonics. The system can provide improved resolution particularly of the characteristics of in-phase secondary signals received from terrain being surveyed.

Abstract: A transmitter, to be used in an airborne or ground electromagnetic survey system for detecting conductive bodies in an area, said system being adapted to generate a frequency modulated signal and radiating it to the said area, the said transmitter being provided with a power supply means being adapted to be connected by switch means to at least two circuits, each circuit comprising a radiating means, said radiating means being adapted to be connected to the power supply means, in such a way that assembled radiation means are present, each circuit comprising a radiating means being connected by its own switch to the said power supply means.

Abstract: An information system for communicating information from each of a plurality of separate locations to each of a plurality of mobile objects includes a beacon at each location and a beacon triggering and detecting apparatus mounted on each object. Each beacon triggering and detecting apparatus is assigned a predetermined and unique time window within a common system cycle. During the initial portion of its window, the beacon triggering and detecting apparatus transmits a trigger signal at a frequency f.sub.1, with the trigger signal as transmitted having a substantially constant amplitude and with frequency f.sub.1 being chosen so that the intensity of the trigger signal decays as the cube of radial distance from the object. If the object is within a predetermined beacon trigger range of a location, the beacon at that location detects the trigger signal and transmits a beacon signal at a frequency f.sub.2 (substantially greater than frequency f.sub.

Abstract: According to the method, a primary electromagnetic field, defined by a waveform of known shape and containing a plurality of frequency components, is directed towards a target zone. Signals are received in the vicinity of the target zone which are attributable to eddy currents in conductors present in the target zone and direct coupling with the primary field. A reference signal having a complex waveform similar to that of the primary field is generated artificially and the reference signal is compared with the received signals in a digital computer in such a manner as to minimize the amount of signal present in the received signal which is attributable to direct coupling with the primary field. The resulting received signal may then be correlated with a plurality of stored reference waveforms in order to obtain the best fit.

Abstract: The present invention relates to a method and apparatus for determining the electrical conductivity of the ground, particularly in connection with aerial prospecting, with the use of a transmitter unit (S) and a receiver unit (M) located at a distance from said transmitter unit and particularly carried by an aircraft (21). The transmitter is arranged to generate an electromagnetic field which induces an electric current in the ground, and the receiver is arranged to measure magnetic and electric fields induced by said current at the measuring site, said fields representing a measurement of said electrical conductivity and variations therein. The magnet field from the transmitter is transmitted horizontally as is directed transversally of an imaginary line that connects the transmitter (S) with the receiver (M). The electric field E from the transmitter is measured in the receiver in a radial direction to the transmitter.

Abstract: Method and apparatus for detecting tunnels, voids or other anomalies bene an area of the earth's surface wherein an oscillator couples a current into two conductors laid parallel to each other to generate two magnetic fields in the earth beneath the area. The magnetic field is measured along a line midway between the two horizontal conductors to detect for an increase in the measured field which is an indication of the presence of an anomaly.

Abstract: Improved method and apparatus for detecting anomalies beneath an area of earth's surface wherein an oscillator couples a current into two conductors laid parallel to each other to generate two magnetic fields in the earth beneath the area. The magnetic field is measured along a line midway between the two horizontal conductors to detect for an increase in the measured field which is an indication of the presence of an anomaly.

Abstract: A method and apparatus for controlling electric current in loads that are essentially inductive, such that sparking and "ringing" current problems are reduced or eliminated. The circuit apparatus employs a pair of solid state switches (each of which switch may be an array of connected or parallel solid state switching devices such as transistors) and means for controlling those switches such that a power supply supplying two d.c. voltages (e.g. positive 150 volts d.c. and negative 150 volts d.c.) at low resistance may be connected across an essentially inductive load (e.g. a 6 gauge wire loop one hundred meters in diameter) alternatively and such that the first solid state switch is turned off and the second is turned on such that both are not on at the same time but the first turned on and the other on in less time than the inductive time constant (L/R) so that the load is essentially always presented with a low resistance path across its input.

Abstract: A method and apparatus for radio geophysical surveying includes measuring the relative magnitude and phase of radio frequency signal components reflected from subterranean formations. The apparatus comprises a transmitter selectively connected to a vertical antenna and a loop antenna, and a pair of receivers, one receiver being connected to a vertical antenna and the other connected to a loop antenna. A surface propagated calibration signal is transmitted and is received by each of the receivers. The outputs of the receivers are connected to the input of a difference amplifier, a difference signal is generated, and the magnitude and phase of the difference signal are measured and recorded. A survey signal, including surface propagated components and earth propagated components, is then transmitted. The survey signal is received, a difference signal is generated, and the magnitude and phase thereof are measured.

Abstract: 1. An underwater eddy current detector comprising a hollow elongated conding member, said conducting member having a plurality of longitudinal conducting paths forming portions of the exterior surface of said conducting member, a portion of said conducting member formed of material having conductivity of lesser degree than said conducting member and arranged to direct eddy currents induced in said conducting member to said conducting paths, a plurality of toroidal detector coils wound upon annular laminated structures, each of said detector coils encircling one of said conducting paths, whereby a potential which is proportional to a detected signal is induced in said coils when said conducting member is submerged in a conducting medium and located in the path of flow of a plurality of currents flowing in said conducting medium.

Abstract: The conductivity of horizontally layered terrain is investigated by using spaced transmitter and receiver coils above the terrain, the transmitter coil frequency being low enough relative to the coil separation and the terrain conductivity so that the quadrature component of the received signal is essentially the sum of non-interactive components attributable to the separate layers and directly proportional to the conductivity of those layers, a plurality of measurements being made using different measurement parameters so that unknown thickness and/or conductivity parameters of the layers may be ascertained.

Abstract: Instrumentation and procedures for detecting geological anomalies occurring in layered coal formations. The instrumentation comprises a medium frequency continuous wave narrowband FM transmitter and receiver pair. Two instrument configurations are disclosed with one being a portable instrument for use with an existing mined area and another being a downhole instrument for insertion into boreholes in unmined areas. Survey procedures are provided to detect anomolies through signal attenuation, path attenuation and signal phase shift. Continuity measurements provide data to determine the existance of anomalies. Tomographic techniques are employed to provide a visual image of the anomaly. Computer aided reconstruction techniques provide such visual images from the generated data.

Abstract: Apparatus and method for detecting geological anomalies occuring in geological formations. The instrumentation comprises a medium frequency continuous wave narrowband FM transmitter and receiver pair. Two instrument configurations are downhole instruments for insertion into boreholes. Survey procedures are provided to detect anomalies through signal attenuation, path attenuation and signal phase shift. Continuity measurements at different depths in the drillholes provide data to determine the existence of anomalies. Tomographic techniques are employed to provide a visual image of the anomaly. Computer aided reconstruction techniques provide such visual images from the generated data.