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: A transient electromagnetic method for detecting irregularities on container walls by measuring wall thickness. The method utilizes a transmitting antenna and a separate receiving antenna arranged in a loop-loop configuration. The transmitting antenna induces current into the container wall and the receiving antenna and the receiver detect the decay of the induced current, which is then analyzed to detect wall thickness. A receiving antenna array of many receiving antennas is used to increase the spatial resolution. Simultaneous measurement of the induced current by the receiving antennas reduces noise that is coherent across the array. Use of a noise antenna located so as to be unaffected by the transmitting antenna further reduces noise. The received signal from the receiving antenna array is displayed on a two-dimensional display in a spatial arrangement that corresponds to the spatial arrangement of the receiving antennas.

Abstract: A borehole telemetry system has a transmitter located in the borehole, a surface receiver, and surface signal sensors for receiving the transmitted signal. There are usually plural sources of electromagnetic noise at a well site which degrade the usefulness of the telemetry system. The method places noise sensors where the reception of noise is maximized. Simultaneous measurements are taken of the ambient noise with the noise sensors and the signal sensors. The relationship between the measurements of the noise and signal sensors is determined. The transmitted signal is then received by the signal sensors and simultaneous measurements of the ambient noise are made by the noise sensors. The noise portion of the transmitted signal as received by the signal sensors is determined from the simultaneous noise measurements and the determined relationship. A received signal having reduced noise is then produced by removing the noise portion.

Abstract: A method for reducing impulsive noise in electromagnetic geophysical data utilizes a receiving antenna and one or more noise sensors. The type of noise sensor used depends on the type of impulsive noise which is to be monitored. Motion noise is monitored with a tilt meter or similar motion sensor. Impulsive electromagnetic noise is monitored with an electric or magnetic field sensor which is located so as to receive impulsive noise while minimizing the reception of the electromagnetic signal of interest. Impulsive noise is monitored without the electromagnetic signal of interest for a short period of time to enable the determination of a threshold noise value. Then, the impulsive noise is monitored simultaneously with the electromagnetic signal of interest, wherein the impulsive noise is received by the noise sensor and the signal of interest is received by the receiving antenna.

Abstract: A transient electromagnetic method for detecting irregularities on container walls by measuring wall thickness. The method utilizes a transmitting antenna and a separate receiving antenna arranged in a loop-loop configuration. The transmitting antenna induces current into the container wall and the receiving antenna and the receiver detect the decay of the induced current, which is then analyzed to detect wall thickness. A receiving antenna array of many receiving antennas is used to increase the spatial resolution. Simultaneous measurement of the induced current by the receiving antennas reduces noise that is coherent across the array. Use of a noise antenna located so as to be unaffected by the transmitting antenna further reduces noise. The received signal from the receiving antenna array is displayed on a two-dimensional display in a spatial arrangement that corresponds to the spatial arrangement of the receiving antennas.

Abstract: There is disclosed a method for detecting corrosion on the walls of conductive containers wherein a transmitting antenna induces a current into a portion of the container wall and the decay of the induced current is detected by a receiving antenna, with a record of the decay of the induced current being created. The record is interpreted to determine the thickness of the container wall portion and the presence or absence of corrosion is inferred. One method of interpretation uses reference records from container walls having known parameters for comparison. Another method of interpretation examines the times that the induced current reaches the container wall portion surface that is farthest from the antennas.

Abstract: There is disclosed a method for directly detecting corrosion on the walls of conductive containers wherein a transmitting antenna induces a current into a portion of the container wall and the decay of the induced current is detected by a receiving antenna, with a record of the decay of the induced current being created. The record is interpreted to determine the presence or absence of a corrosion component, with the corrosion component being caused by the presence of corrosion products having superparamagnetic properties.

Abstract: A method for reducing noise in electromagnetic geophysical exploration data simultaneously measures three orthogonal components of the ambient noise to produce noise records and simultaneously measures three orthogonal components of the decay of current induced into the earth to produce response records. In measuring the records, the receiving antenna is positioned near the electromagnetic center of the transmitting antenna, whereby the maximum component of the induced current decay signal is vertical or perpendicular to the strata in the earth. The impulse response of the earth is determined from the noise records. The noise portion of the vertical response record is determined from the impulse response and the non-vertical response records, whereby the noise portion is removed from the vertical response record.