Abstract: A suspension net is provided for distributing tension forces from a tow rope to an electromagnetic bird used for geophysical surveying. The suspension net allows large transmitter loop sizes, and the net structure generally avoids rope confusions that can occur during lift-up.

Abstract: An airborne electromagnetic survey system for conducting geological mapping is disclosed. A transmitter closed loop structure is used in the system and is designed for connection to a towing airborne vehicle. The transmitter loop structure comprises a plurality of interconnected loop segments, and transmitting means are fitted to at least one of the loop segments for generating and transmitting an earthbound primary electromagnetic field effective for geological surveying. Sensing means are fitted to the loop segments for receiving and sensing a vertical component of a secondary resulting electromagnetic field which arises from an interaction of the primary electromagnetic field with ground bodies that are traversed by the sensing means, while simultaneously nulling the primary electromagnetic field.

Abstract: A surveying instrument performs tracking of a target by controlling an orientation of a measuring unit relative to the target in two different angular directions. The control in one angular direction is based on detected light intensities which are modulated according to a first time pattern, and control of the orientation in the other angular direction is based on detected light intensities modulated according to a second time pattern just different from the first time pattern.

Abstract: A method of determining the nature of a submarine or subterranean reservoir having an electromagnetic characteristic is described. The method comprises analyzing data associated with the application of a time varying electromagnetic field from above the reservoir using a data analysis methodology that does not utilize an estimate of the reservoir's geometry in determining one or more characteristics of the reservoir.

Abstract: A system for the electronic detection of military threats includes an electromagnetic (EM) gradiometer for detecting secondary EM waves scattered from objects illuminated by a primary EM wave existent in a local area. A right magnetic dipole antenna and a left magnetic dipole antenna are included in the EM gradiometer for receiving the secondary EM waves and able to reject the primary EM wave. A synchronizer derives a reference signal to the EM gradiometer from the primary EM wave. A synchronous detection processor makes measurements of the phase and amplitude of the secondary EM waves. A graphical user interface (GUI) is used to display information about the location of objects assessed to be threats in the local area that were computed from the measurements of the phase and amplitude. A vehicle may be used to transport the EM gradiometer over the local area during periods the objects are being radio illuminated.

Abstract: A method and system for geophysical surveying. A non-rigid airship having a self-supporting gas envelope and propulsion units coupled to the gas envelope, the propulsion units being configured to control the steering and altitude of the airship without the aid of a rudder or elevators, is provided with geophysical survey equipment, and geophysical data is collected while flying the airship. Also a method for geophysical surveying that includes providing a first airship with a first set of geophysical survey equipment, providing a second airship with a second set of geophysical survey equipment that is complimentary to the first set, and conducting an airborne geophysical survey by flying the first airship and the second airship along a designated flight path within a predetermined range of each other.

Abstract: The present invention is a double-suspension receiver coil apparatus and system for conducting electromagnetic surveys including, both ground-based and airborne measurements. The present invention includes at least one receiver coil suspended by way of first suspension members within an inner frame and said inner frame being suspended by second suspension members within an inner ring which is further enclosed within an outer frame. The double-suspension receiver coil apparatus functions so as to maintain the receiver coil position while minimizing vibrations in order to achieve a high signal-to-noise ratio and enable accurate measurements. The receiver coil may be in an airborne system in a near-horizontal position or in a ground system in a vertical position.

Abstract: A method for identifying a possible porphyry copper deposit which includes flying an airborne sensor over a survey area measuring natural electromagnetic fields in the survey area, and then determining, in dependence on the measured natural electromagnetic fields, if one or more sub-areas in the survey area have a resistivity pattern that corresponds to a predetermined resistivity signature for a porphyry copper deposit.

Abstract: An airborne time domain electromagnetic survey system is provided. The system and apparatus of the present invention are able to address the interest in exploring base metals and uranium deposits at depths approaching 1 kilometer. It encompasses a transmitter coil having a large magnetic dipole moment, flight stability, which is light weight, compatible with small helicopters, and can be transported, setup and repaired in the field. It is of a semi-rigid modular structure that can decrease the incidence of damage or breakage during take-off or landing in rough terrain.

Abstract: A method and system for synchronizing geophysical survey data is provided. Detection of geophysically significant subsurface anomalies potentially associated with ore bodies or hydrocarbon deposits can be made by vehicle mounted surface or airborne regional gravitational studies. Recorded geophysical survey data is processed to synchronize data collected by various sensors. Data from the various sensors is synchronized based on position coordinates corresponding to locations where the data was collected. In this manner, at one specific location on Earth, the electromagnetic reading, magnetometer reading, gravimeter reading, and altimeter reading can all be associated together so that many characteristics of the specific location can be identified.

Abstract: An airborne electromagnetic survey system for conducting geological mapping is disclosed. A transmitter closed loop structure is used in the system and is designed for connection to a towing airborne vehicle. The transmitter loop structure comprises a plurality of interconnected loop segments, and transmitting means are fitted to at least one of the loop segments for generating and transmitting an earthbound primary electromagnetic field effective for geological surveying. Sensing means are fitted to the loop segments for receiving and sensing a vertical component of a secondary resulting electromagnetic field which arises from an interaction of the primary electromagnetic field with ground bodies that are traversed by the sensing means, while simultaneously nulling the primary electromagnetic field.

Abstract: An aerial electronic system for detection of surface and underground threats comprises an electromagnetic (EM) gradiometer flown aloft over the possible ground and underground threats to a convoy. The EM gradiometer is disposed in a Styrofoam torpedo shaped pod that is towed in flight behind an airplane. An illumination transmitter and loop antenna mounted to the airplane radiate a primary EM wave that travels down to the ground surface and penetrates beneath. Frequencies of 80 KHz to 1 MHz are selected according to whether the targets are laying on the surface or deeply buried. Detonation wire pairs, buried cables and pipes, and other conductors will re-radiate a secondary wave that can be sensed by the EM gradiometer. A reference sample of the transmitter signal is carried down a fiberoptic from the airplane to the towed pod. This signal is used in the synchronous detection to measure the secondary EM wave phase.

Abstract: An airborne electromagnetic prospecting system (10) is disclosed. The system (10) comprises a transmitter loop structure (12) hat is attached to, and arranged to be towed by, a helicopter (14). A transmitter (22) is fitted to the transmitter loop structure (12) for transmitting a primary electromagnetic field. A high drag bird (26) is attached to, and arranged to be towed by, the transmitter loop structure (12). A receiver (38) is fitted to the high drag bird (26) for receiving a primary and secondary resulting electromagnetic field, the secondary field arising from the interaction of the primary field with ground conductors that are traversed by the helicopter (14).

Abstract: A suspension net is provided for distributing tension forces from a tow rope to an electromagnetic bird used for geophysical surveying. The suspension net allows large transmitter loop sizes, and the net structure generally avoids rope confusions that can occur during lift-up.

Abstract: This invention concerns a method of making airborne geophysical measurements. Such measurements may be made from fixed or moving wing airplanes or dirigibles. The method comprises the following steps: taking first real time measurements from one, or more, geophysical instruments mounted in an aircraft to produce geophysical data related to the ground below that instrument. Taking second real time measurements from navigation and mapping instruments associated with or carried by the aircraft. Computing a background response of each geophysical instrument using the second real time measurements to take account of its time varying altitude, and the time varying topography of the ground below it. Adjusting an operating or data processing condition of each geophysical instrument using the respective background response and the instrument's attitude to enhance the performance of that instrument.

Abstract: An aerial electronic system for detection of surface and underground threats comprises an electromagnetic (EM) gradiometer flown aloft over the possible ground and underground threats to a convoy. The EM gradiometer is disposed in a Styrofoam torpedo shaped pod that is towed in flight behind an airplane. An illumination transmitter and loop antenna mounted to the airplane radiate a primary EM wave that travels down to the ground surface and penetrates beneath. Frequencies of 80 KHz to 1 MHz are selected according to whether the targets are laying on the surface or deeply buried. Detonation wire pairs, buried cables and pipes, and other conductors will re-radiate a secondary wave that can be sensed by the EM gradiometer. A reference sample of the transmitter signal is carried down a fiberoptic from the airplane to the towed pod. This signal is used in the synchronous detection to measure the secondary EM wave phase.

Abstract: A portable multispectral data acquisition system for use on a vehicle such as an aircraft comprises a plurality of gyroscope-stabilized remote sensing devices synchronized to simultaneously capture images of a common spatial area in both visible and invisible bands of the electromagnetic spectrum, a computer and digital recorder to record and correlate the captured images with temporospatial reference information, image processing software to stack or layer the images and to extract and compare the images in order to identify and filter hidden or subsurface anomalies that are invisible to the naked eye, and additional image processing software to orthorectify the images to a three-dimensional digital terrain map and to stitch adjacent images together into a mosaic. Methods for using the portable multispectral data acquisition system are also provided.

Abstract: An active system and method for determining the physical characteristics and geological composition of subterranean formations is described. Plane polarized electromagnetic waves at specific frequencies are transmitted by a mobile transmitting antenna held stationary in the far-field about a prospecting point. The plane polarized electromagnetic waves penetrate the Earth and return to the surface to be picked up at a separate mobile receiving antenna held stationary about a prospecting point. The differences in intensity and polarization between transmitted and received waves are measured and carry geological information. Further, a coordinated series of transmissions, receptions, and measurements are made, in which the angle of incidence and the revolution angle about a centerline emanating perpendicularly from the prospecting point are carefully and systematically varied and repeated for a specific set of frequencies.

Abstract: A system and method determines the probability of oil or mineral deposits. At least one data collection device collects elevation slope, magnetic and gravity data sets for a predetermined area of the earth's surface. A processor receives the elevation slope, magnetic and gravity data sets and applies the gravity and magnetic data sets in a transfer function to link the elevation slope data set to the likely presence of oil or mineral deposits.

Abstract: An airborne exploration system used with an aircraft for exploration of oil and gas, mineral deposits and aquifers. The survey system uses natural electromagnetic EM fields as an energy source. The exploration system includes at least one non-directional, wideband, total electric field, water sensor. The water sensor includes a water container filled with water and adapted for mounting on an aircraft. The water container has a pair of conductive metal bands mounted around opposite ends thereof. The metal bands provide a capacitive electrical coupling with the water in the container. The water container has a diameter substantial the size as a length of the container. Therefore, the sensor responds to an electric field substantially independent of the relative orientation of the electric field. The bands are electrically connected to a computer data processing unit mounted on the aircraft.

Abstract: An airborne time domain electromagnetic surveying system is provided. The system includes a tow assembly with a flexible support frame. The flexible support frame spaced apart from the aircraft includes a transmitter section with a transmitter loop and a receiver section with a sensor aligned with the central axis of the transmitter section. The flexible support frame has a lightweight modular structure that enables the surface area of the transmitter section to be increased and decreased to suit particular survey applications. The transmitter loop sends a pulse in an “ON” interval, and in an “OFF” interval the sensor measures the earth response to the pulse. The tow assembly also includes a sensor for generating selected survey data in the “ON” interval. A transmitter driver enables the creation of earthbound pulse. The system components are linked to a computer and control computer program linked thereto for controlling the functions thereof.

Abstract: An induction logging tool is used on a MWD bottom hole assembly. Due to the finite, nonzero, conductivity of the mandrel, conventional multi frequency focusing (MFF) does not work. A correction is made to the induction logging data to give measurements simulating a perfectly conducting mandrel. MFF can then be applied to the corrected data to give formation resistivities.

Abstract: An airborne exploration system used with an aircraft for shallow and deep exploration for oil and gas, mineral deposits and aquifers. The survey system uses natural electromagnetic EM fields as an energy source. The exploration system includes a pair of aerodynamic housing pods adapted for mounting on wing tips of the aircraft. The housing pods include electric field sensors with three orthogonal electric dipoles oriented along an X, Y and Z axis. An optional third set of orthogonal electric dipoles can be mounted in the tail of the aircraft. The field sensors are electrically attached to angular motion detectors mounted inside housing pods. The motion detectors are used for compensating for errors caused by angular motion of the aircraft when in the presence of strong electric field gradients. The system also includes a total field magnetometer mounted in the aircraft.

Abstract: A method of improving pulse inductive metal detector sensitivity by minimizing adverse ground responses and transmitter coil transients is disclosed. The method provides a calibration mode for a typical pulsed EMI metal detector. The purpose of the calibration mode is to determine and record a nulling signal representative of the transmitter coil coupling to the receiver coil and a ground response that has no metal. The nulling signal is then used during normal operation of the metal detector by combining it with the instant receiver coil signal in a difference amplifier. The difference amplifier effectively subtracts the nulling signal from the instant signal yielding a response signal that has removed the ground response that may be present in the instant signal. The metal detector can be periodically re-calibrated. It may also be re-calibrated upon discovery of a metal target to provide the most up to date nulling signal for the ground around the metal target.

Abstract: A system, computer product and method for generating geophysical data is provided. At least one airborne sensor unit is provided which measures low frequency natural electromagnetic fields. Geophysical data is extrapolated from the tilt angles of the electromagnetic field by a computer running a data processing application. The system further includes a spatial attitude detection facility. The data processing application filters out distortions to the tilt angles caused by movement of the airborne sensor unit. The system further includes facilities for filtering out electronic noise.

Abstract: A airborne electromagnetic induction (EMI) detection apparatus and system. In accordance with one embodiment, the EMI detection apparatus includes a transmitter element in the form of a transmitter coil that emits a primary, multi-frequency component magnetic field which induces a secondary magnetic field in an external body. A receiver element in the form of a receiver coil is mounted in a horizontal loop-loop orientation with respect to the transmitter coil and receives the secondary magnetic field. The detection apparatus further includes a magnetic shield disposed around the receiver coil to limit the lateral footprint diameter observed by the receiving element and to shield the receiver coil from the primary magnetic field and other external electromagnetic radiation to improve the gain and resolution of the detection apparatus.

Abstract: A magnetotelluric geophysical survey system used with an airborne survey bird for natural resource exploration of oil and gas, mineral deposits and aquifers. The survey system uses natural electromagnetic EM fields as an energy source. The magnetotelluric airborne survey system includes an aerodynamic airborne survey bird adapted for being towed behind a helicopter or fixed wing aircraft. The survey system can also be incorporated into a fixed wind aircraft. The survey system includes a non-conductive nose boom on the survey bird with orthogonal electric dipoles for measuring electric fields from 0.01 Hz up to 480 Hz. An angular motion detector is mounted inside the bird and used for compensating for errors caused by angular motion of the bird when in the presence of strong electric field gradients. The survey bird can use a single magnetometer or pairs of magnetometers for measuring electromagnetic gradients.

Abstract: A wheel speed calculation method wherein, when both rising and falling edges occur, the wheel speed is calculated using both the edges, when either of the edges does not occur, the wheel speed is calculated using both the edges in such a manner that for the edge not occurring, the preceding calculation value or the calculation value provided by assuming that one occurred within the temporary time, whichever is the lower, is selected. Further, neither of the rising and falling edges occurs, the minimum value of the two calculation values provided by assuming that only one edge occurred within the temporary time and the calculation value provided by assuming that only one rising edge and only one falling edge occurred within the temporary time or the calculation value of the preceding wheel speed, whichever is the lower, is selected as the wheel speed.

Abstract: A housing and bucking coil and receiving coil system for a helicopter towed concentric coil electromagnetic survey system that reduces micro phonic and primary field noise. The device includes an isolation housing, a bucking coil and receiving coil assembly with structural members to rigidly join the two coils together and a suspension system to suspend the joined bucking and receiving coils, in a floating manner, by bungee cords or similar non-metallic vibration dampening devices.

Abstract: A system, computer product and method for generating geophysical data is provided. At least one airborne sensor unit is provided which measures low frequency natural electromagnetic fields. Geophysical data is extrapolated from the tilt angles of the electromagnetic field by a computer running a data processing application. The system further includes a spatial attitude detection facility. The data processing application filters out distortions to the tilt angles caused by movement of the airborne sensor unit. The system further includes facilities for filtering out electronic noise.

Abstract: Disclosed is a system of making an olefin derivative from a dilute olefin feed. Dilute olefin is sent to an olefin reaction unit to form an olefin derivative product. The olefin derivative product is recovered from the reaction unit while a vent stream is also removed. Olefin is separated from the vent stream, and the olefin is sent to the olefin reaction unit for additional processing.

Abstract: A frequency domain electromagnetic geophysical mapping instrument has a transmitter, a transmitter coil connected to the transmitter, the transmitter generating current pulse waveforms formed by half-sinusoidal output waveform segments of a waveform having a frequency equal to a resonant frequency of the transmitter coil, and a receiver, in which the transmitter generates current pulses including pulses comprising a plurality of immediately successive half-sinusoidal waveform segments of common polarity. The pulses immediately succeed each other and are of alternating polarity. The pulse lengths may in this case be equal, or vary in a manner providing a desired output spectrum, for example according to a pseudo-random sequence.

Abstract: A method for creating signal unidirectionality in electronic circuits is disclosed. This invention describes a method for achieving unidirectionality in an electronic circuit with an input side having a signal source and an output side with a load comprising detecting the current passing through the load on the output side, bypassing a portion of the current passing through the load on the output side, and feeding the bypassed portion of the current on the output side to the input side to achieve unidirectionality. Specifically, unidirectionality in an electronic circuit is accomplished by applying feedback such that the impedance looking into the input of the amplifier is increased. These methods are particularly applicable to negative resistance amplifier circuits.

Abstract: A measuring apparatus has a magnetizing head for magnetizing a magnetic layer of a specimen, and a detecting sensor for detecting a magnetization of a magnetized area which has been magnetized by the magnetizing head. The magnetization detected by the detecting sensor is supplied via a sensor amplifier to a controller. Based on the supplied magnetization, the controller determines the thickness of the magnetic layer from a magnetization to magnetic layer thickness conversion table or formula. The thickness of the magnetic layer can therefore be measured accurately in a short period of time.

Abstract: A towed aircraft for use in an airborne electromagnetic geophysical prospecting system which includes a transmitting antenna and power generating means for powering the antenna. A bird to which is mounted a receiving antenna may be towed by the towed aircraft.

Abstract: Apparatus for remotely determining the amount of current I flowing in a long, linear conductor, comprising a first sensor for measuring at a first location a magnetic field H arising due to current flow, a second sensor for measuring at a second location the same magnetic field H, a mounting mechanism for fixing the position of the first and second sensors in an unchanging, spaced-apart mutual configuration, calculating apparatus for calculating the vertical gradient H′ of the magnetic field on the basis of measurements made by the sensors, and further calculating apparatus for determining the current I on the basis of the equation I=H2/H′ where k is a constant.

Abstract: In a time domain electromagnetic mapping technique of the type using transmitter pulses of half-sinusoidal waveform, with the half sinusoids being segments of a sinusoidal waveform having a frequency and corresponding to a resonant frequency of the transmitter coil, an improved current fall time at the end of each pulse is obtained by forming each transmitter pulse of plural immediately successive half sinusoids, the transmitter coil being tuned to an appropriately increased resonant frequency relative to the pulse repetition rate. Circuits for generating the improved pulse waveforms are disclosed.

Abstract: This invention relates generally to a method and system for synchronizing the timing of events between and among vessels using a common timing reference.

Abstract: A system for assistance in landing a helicopter and for the detection of electro-magnetic anomalies utilizing helicopter blades as carriers of receiving devices in a wide spectrum of electro-magnetic fields with a predicted sensitivity and resolution far in advance of previous systems.

Abstract: A method of interrogating a volume of material beneath the ground. According to the method a transmitter is located to extend over and be supported by a surface area of ground encompassing and beneath which lies the volume of material. A generator device is used to generate transient electromagnetic pulses within the transmitter. An airborne vehicle, aboard which is a detector, is used to fly over the area of ground. The detector and the generator are synchronized to one another so that the detector has information regarding when the transient electromagnetic pulses are generated. The detector detects the resultant electromagnetic field of the transient electromagnetic pulses, which have certain magnitude and temporal characteristics. A received signal is formed by the detector, which signal is dependant upon the magnitude and the temporal characteristics of the detected electromagnetic fields. The received signal is thereafter processed to determine characteristics of the volume of material.

Abstract: A geophysical survey system including a remotely piloted vehicle, a geophysical sensing payload mounted thereon and ground based control and data receiving means.

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 of locating potential oil and gas reservoirs in the earth utilizing a satellite equipped to receive reflected solar energy from the earth at at least one selected frequency band, transmitting signals indicative of the received reflected energy to the earth, recording the received signals in a manner to provide a map of the earth's surface, filtering the received signals to provide signals representative of bands characterized by hydrocarbon gas absorption of the solar energy, and displaying the filtered signals, the area of hydrocarbon absorption being indicated by low intensity levels. The satellite system can be equipped with a coherent infrared irradiation system which scans the area of obsrvation, utilizing a selected infrared wave length beam to augment normal solar radiation at those wave lengths most effective for detecting the hydrocarbon gas cloud which appears above an oil or gas reservoir.

Abstract: A method 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 comprising a known petroleum deposit and known barren locations (a stage of system instruction) and then over an unknown area to be explored (a stage of actual prospecting). The enormous volume of data obtained in both stages is processed electronically, using pattern recognition theory, into a probability level of the hydrocarbon presence or absence for all measuring points over the unknown area. In the stage of system instruction, the detected signal deviations are converted into factors of discriminant functions by substituting the high absolute probability levels for known hydrocarbon deposit and barren locations (above +0.8 and below -0.8, respectively) into these functions.

Abstract: A method and apparatus for improving signals used for detecting conductive bodies in an area by means of an airborne electromagnetic survey system, comprising the steps of generating and transmitting an AC primary field signal, the frequency spectrum of which comprises a DC component or a low frequency component, and radiating this primary field signal to the said area and receiving induced secondary field signals which are generated by the said conductive bodies and further comprising the step of processing the received secondary field signals and representing the processed signals in order to derive information whether or not conductive bodies in the said area are present.

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: The technologies of radar, exploration seismology, and air or space transportation, are combined to provide a highly-mobile and economical system of geophysical exploration for petroleum and other mineral deposits. Use is made of the Seismo-electric (SE) and Electro-seismic (ES) effects to momentarily alter the reflection and scattering from, and absorption in, the earth's surface, of electromagnetic (radar) waves transmitted from, and received by, an aircraft or space vehicle, to thereby modulate seismic information on the reflected, scattered and received waves. In this improvement, the received waves, as represented by their transduced electric counterparts, are divided into two paths having different times of transmission, and synchronously re-combined to enhance systematic or meaningful information and remove non-systematic disturbances and random noise.

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: 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.