Abstract: A method for determining a formation response form a detected electromagnetic signal resulting from a first electromagnetic signal imparted into a subsurface earth formation and from a second electromagnetic signal imparted into the formation, the first and second signals being imparted substantially contemporaneously. The detected signals are deconvolved using the first electromagnetic signal. The deconvolved detected signal is used to estimate the formation response to the first electromagnetic signal. Convolving the estimated formation response from the estimated formation response with the first electromagnetic signal and subtracting a result of the convulsion with the first electromagnetic signal from the detected signal.

Abstract: A method for reducing effect of motion on electromagnetic signals detected while moving an electromagnetic receiver through a body of water includes measuring a parameter related to an amount of current passed through an electromagnetic transmitter to induce an electromagnetic field in subsurface formations. A magnetic field proximate the electromagnetic receiver is measured. A transmitter portion of the measured magnetic field is estimated from the measured parameter. A motion portion of the measured magnetic field is estimated from the measured magnetic field and the estimated transmitter portion. A voltage induced in the receiver is estimated from the estimated motion portion. Signals detected by the receiver are corrected using the estimated voltage.

Abstract: A method for removing the effects of an airwave from marine electromagnetic data comprising providing an electromagnetic source and at least one receiver in the water; measuring the electromagnetic response at a first source-receiver separation; determining a scaled version of the airwave response at a source-receiver separation where the earth response is negligible and using the scaled airwave response to determine the earth response measured at the first separation. Using this method, an improved estimate of the earth's response can be achieved.

Abstract: A method for seismic exploration of subsurface rock formations includes actuating an impulsive seismic energy source proximate the rock formations. A non-impulsive seismic energy source is actuated. A near field waveform of each of the impulsive and non-impulsive seismic energy sources is detected. A far field waveform of the combined output of the impulsive and non-impulsive seismic energy sources is determined from the near field waveforms. An impulse response of the subsurface rock formations is determined by deconvolving the far field waveform with detected seismic signals.

Abstract: A method for measuring resistivity variations in the earth comprising passing a transient current between two source electrodes; measuring the transient current at the source electrodes; measuring the resultant transient voltage between at least one pair of receiver electrodes; estimating one or more processing functions for applying to the measured input current to provide a step current profile, and applying the same one or more processing functions to the measured voltage to provide an estimate of the step response voltage between the receivers, using both the step current and the estimated step response voltage to determine the resulting apparent earth resistance, and using the apparent earth resistance to determine the resistivity of the earth.

Abstract: A method for electromagnetic exploration includes imparting a first electromagnetic signal into subsurface formations and imparting a second electromagnetic signal into the formations substantially contemporaneously with imparting the first electromagnetic signal. The first and second electromagnetic signals are substantially uncorrelated with each other. A combined electromagnetic response of the formations to the first and second imparted electromagnetic signals is detected. A response of the formations to each of the first and the second imparted signals is determined from the detected response.

Abstract: A method for electromagnetic surveying subsurface formations includes inducing an electromagnetic field in the subsurface formations by passing electric current through a transmitter. Response of the subsurface formations to the induced electromagnetic field is detected at a first plurality of spaced apart positions disposed longitudinally within a bipole length of the transmitter. A direct induction response is removed from the detected response.

Abstract: A method for determining resistivity distribution of formations below a bottom of a body of water from transient electromagnetic signals acquired by imparting a transient electromagnetic field into the water and detecting an electromagnetic response thereto at a plurality of spaced apart positions from a place of the imparting includes simulating an air wave response at each of the plurality of spaced apart positions. The simulated air wave response is subtracted from the detected response to produce a subsurface impulse response at each of the plurality of positions. The subsurface impulse responses are used to determine the resistivity distribution.

Abstract: A method for electromagnetic exploration includes imparting a first electromagnetic signal into subsurface formations from a first location and imparting a second electromagnetic signal into the formations from a second location substantially contemporaneously with imparting the first electromagnetic signal. The first and second electromagnetic signals are substantially uncorrelated with each other. A combined electromagnetic response of the formations to the first and second imparted electromagnetic signals is detected at a third location. A response of the formations to each of the first and the second imparted signals is determined from the detected response.

Abstract: A method for seismic exploration of subsurface rock formations includes actuating an impulsive seismic energy source proximate the rock formations. A non-impulsive seismic energy source is actuated. A near field waveform of each of the impulsive and non-impulsive seismic energy sources is detected. A far field waveform of the combined output of the impulsive and non-impulsive seismic energy sources is determined from the near field waveforms. An impulse response of the subsurface rock formations is determined by deconvolving the far field waveform with detected seismic signals.

Abstract: A method for determining resistivity distribution of formations below a bottom of a body of water from transient electromagnetic signals acquired by imparting a transient electromagnetic field into the water and detecting an electromagnetic response thereto at a plurality of spaced apart positions from a place of the imparting includes simulating an air wave response at each of the plurality of spaced apart positions. The simulated air wave response is subtracted from the detected response to produce a subsurface impulse response at each of the plurality of positions. The subsurface impulse responses are used to determine the resistivity distribution.

Abstract: A method for measuring resistivity variations in the earth comprising passing a transient current between two source electrodes; measuring the transient current at the source electrodes; measuring the resultant transient voltage between at least one pair of receiver electrodes; estimating one or more processing functions for applying to the measured input current to provide a step current profile, and applying the same one or more processing functions to the measured voltage to provide an estimate of the step response voltage between the receivers, using both the step current and the estimated step response voltage between voltage to determine the resulting apparent earth resistance, and using the apparent earth resistance to determine the resistivity of the earth.

Abstract: A method for measuring the electromagnetic response of formations below the bottom of a body of water includes positioning at least one electromagnetic transmitter and at least one electromagnetic receiver in the body of water each at a selected depth below the water surface. A transient electric current is passed through the at least one transmitter. An electromagnetic signal is detected at the at least one electromagnetic receiver. The depths are selected so that substantially all electromagnetic response to the current passed through the transmitter from the air above the body of water in the detected electromagnetic signal occurs before the beginning of a response originating in the formations below the water bottom.

Abstract: A method for electromagnetic surveying subsurface formations includes inducing an electromagnetic field in the subsurface formations by passing electric current through a transmitter. Response of the subsurface formations to the induced electromagnetic field is detected at a first plurality of spaced apart positions disposed longitudinally within a bipole length of the transmitter. A direct induction response is removed from the detected response.

Abstract: A method for electromagnetic exploration includes imparting a first electromagnetic signal into subsurface formations and imparting a second electromagnetic signal into the formations substantially contemporaneously with imparting the first electromagnetic signal. The first and second electromagnetic signals are substantially uncorrelated with each other. A combined electromagnetic response of the formations to the first and second imparted electromagnetic signals is detected. A response of the formations to each of the first and the second imparted signals is determined from the detected response.

Abstract: A method for attenuating correlated noise in transient electromagnetic survey signals includes producing, from a transient electromagnetic signal measured by a first receiver, an estimate of the Earth response and an estimate of the correlated noise from a portion of the signal occurring before onset of an Earth response, and/or after the Earth response has substantially decayed. An estimate of the correlated noise is determined over the entire measured signal from the first receiver using the estimate of the Earth response. The noise estimate from the entire signal and the portion estimate are used to estimate correlated noise in transient signals from at least a second receiver.

Abstract: A method for reducing effect of motion on electromagnetic signals detected while moving an electromagnetic receiver through a body of water includes measuring a parameter related to an amount of current passed through an electromagnetic transmitter to induce an electromagnetic field in subsurface formations. A magnetic field proximate the electromagnetic receiver is measured. A transmitter portion of the measured magnetic field is estimated from the measured parameter. A motion portion of the measured magnetic field is estimated from the measured magnetic field and the estimated transmitter portion. A voltage induced in the receiver is estimated from the estimated motion portion. Signals detected by the receiver are corrected using the estimated voltage.

Abstract: A method for measuring the electromagnetic response of formations below the bottom of a body of water includes positioning at least one electromagnetic transmitter and at least one electromagnetic receiver in the body of water each at a selected depth below the water surface. A transient electric current is passed through the at least one transmitter. An electromagnetic signal is detected at the at least one electromagnetic receiver. The depths are selected so that substantially all electromagnetic response to the current passed through the transmitter from the air above the body of water in the detected electromagnetic signal occurs before the beginning of a response originating in the formations below the water bottom.

Abstract: A method for electromagnetic exploration includes imparting a first electromagnetic signal into subsurface formations from a first location and imparting a second electromagnetic signal into the formations from a second location substantially contemporaneously with imparting the first electromagnetic signal. The first and second electromagnetic signals are substantially uncorrelated with each other. A combined electromagnetic response of the formations to the first and second imparted electromagnetic signals is detected at a third location. A response of the formations to each of the first and the second imparted signals is determined from the detected response.

Abstract: A method of determining the far-field signature of the seismic wave produced by at least one marine seismic source (20) involving mounting pressure sensing means (2) on the or each seismic source (20) and taking account of both linear and nonlinear components of pressure measurements made by the pressure sensing means (2) to determine the far-field signature of the seismic wave. The invention covers the generation of a seismic wave from a single seismic source and an array of seismic sources and also relates to marine seismic source apparatus.