Abstract: Methods and systems for measuring subsurface electrical conductivity, using first and second sensor coils. The second sensor coil has a smaller effective area and a greater bandwidth than the first sensor coil. The first and second sensor coils are positioned with respect to each other to achieve zero or near zero mutual inductance.

Abstract: Methods and systems for measuring subsurface electrical conductivity, using first and second sensor coils. The second sensor coil has a smaller effective area and a greater bandwidth than the first sensor coil. The first and second sensor coils are positioned with respect to each other to achieve zero or near zero mutual inductance.

Abstract: An electromagnetic detection system comprising: a transmitter loop for generating a primary magnetic field, and spaced apart receiver coils for measuring a secondary magnetic field generated in response to the primary magnetic field.

Abstract: An electromagnetic detection system comprising: a transmitter loop for generating a primary magnetic field, and a first pair of spaced apart receiver coils and second pair of spaced apart receiver coils for measuring a secondary magnetic field generated in response to the primary magnetic field. The transmitter loop drives the transmitter to generate the primary magnetic field.

Abstract: A combined electromagnetic and magnetometer detection system for detecting objects. The system includes a primary electromagnetic transmitter for generating a primary magnetic field; an electromagnetic sensor for sensing secondary magnetic fields generated by a target region subjected to the primary magnetic field; a magnetometer sensor substantially centered at a center of the primary magnetic field; a compensation transmitter for generating a compensating magnetic field that substantially negates the primary magnetic field across the magnetometer sensor; and a signal generator electrically connected to the primary electromagnetic transmitter and the compensation transmitter for driving the transmitters to generate the primary magnetic field and the compensating magnetic field, respectively.

Abstract: A ground conductivity meter that includes a transmitter coil and a receiver coil that are horizontally spaced apart from each other, and a conductivity meter controller connected to the transmitter and receiver coils and including an electronic storage element and at least one processor, the conductivity meter controller being operative to: determine a first conductivity reading in dependence on signals from the receiver coil when the transmitter coil and receiver coil are positioned a predetermined distance above a ground surface in one of a vertical dipole orientation or a horizontal dipole orientation; determine a second conductivity reading in dependence on signals from the receiver coil when the transmitter coil and receiver coil are positioned the predetermined distance above the ground surface in the other of the vertical dipole orientation or horizontal dipole orientation; calculate a correction factor in dependence on the first and second conductivity readings and store the correction factor in the s

Abstract: A ground conductivity meter that includes a transmitter coil and a receiver coil that are horizontally spaced apart from each other, and a conductivity meter controller connected to the transmitter and receiver coils and including an electronic storage element and at least one processor, the conductivity meter controller being operative to: determine a first conductivity reading in dependence on signals from the receiver coil when the transmitter coil and receiver coil are positioned a predetermined distance above a ground surface in one of a vertical dipole orientation or a horizontal dipole orientation; determine a second conductivity reading in dependence on signals from the receiver coil when the transmitter coil and receiver coil are positioned the predetermined distance above the ground surface in the other of the vertical dipole orientation or horizontal dipole orientation; calculate a correction factor in dependence on the first and second conductivity readings and store the correction factor in the s

Abstract: A conductivity meter for measuring conductivity of terrain, including a first transmitter coil, a signal generator connected to the first transmitter coil to supply a time-varying current thereto for inducing eddy currents in the terrain, a first receiver coil horizontally spaced from the first transmitter coil, a temperature sensing device for measuring temperature, and a signal processor, including a memory storing a plurality of temperature dependent correction values, for isolating from a signal received by the first receiver coil a secondary signal representative of a secondary magnetic field generated in the terrain by the eddy currents, and determining an apparent terrain conductivity based on the isolated secondary signal and a selected temperature dependent correction value selected from the stored temperature dependent correction values according to a measured temperature received from the temperature sensing device.

Abstract: A method is disclosed for discriminating electromagnetic responses of metallic objects in soil to application of an electromagnetic pulse from superposed responses due to magnetic susceptibility of the soil, comprising substantially eliminating, from at least a portion of the response, any component having a power law decay characteristic with an exponent which is characteristic of the soil.

Abstract: A method for surveying terrain uses transient magnetic fields transmitted from a coil in plane parallel to and above the terrain, transient voltage response from vertically spaced receiver coils coaxial with and parallel to the transmitter coil being processed to detect highly conductive objects buried in the terrain, with the ratio of the response of the coils optionally being used to estimate the depth of objects. The responses from the coils are scaled in a predetermined ratio to provide cancellation of the response from objects in a layer of terrain at a particular depth, which layer may be at the surface to remove surface responses, or beneath the surface so as to allow surface objects to be differentiated from deeper objects by providing responses of opposite polarity.

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 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: Apparatus is provided which may be made portable and is calibrated to provide direct readings of terrain conductivity. Transmitter and receiver coils are separated by less than one tenth of the electrical skin depth in terrain having a maximum conductivity to be measured, at the frequency of alternating current signal applied to the transmitter coil, and the signals picked up by the receiver coil are processed to cancel received signal components in phase with the transmitted signal and amplify a received quadrature component so as to provide a direct indication of ground conductivity. The in-phase component received direct from the transmitter coil is cancelled by a preset equal and opposite component, and the in-phase component of the secondary signal received from the terrain is substantially cancelled by a form of negative feedback, in order to avoid swamping of the wanted signal.