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 estimating the effects of an airwave in marine electromagnetic data measured using a source and at least one receiver. The method involves measuring the electromagnetic response at two different under water source-receiver separations and using measurements at the larger separation to estimate the airwave response at that separation. The airwave effect in the response measured at the shorter separation can then be determined using the estimated airwave response at the larger separation.

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 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 mapping sub-surface resistivity contrasts comprising making multi-channel transient electromagnetic (MTEM) measurements using at least one electric source with grounded input current electrodes or one magnetic source with current in a wire loop or multi loop and at least one electric field or magnetic field receiver, measuring the resultant earth response simultaneously at each receiver using a known recording system, measuring the system response by measuring directly the current in the wire at the source using effectively the same recording system, using the measured system response to recover the impulse response of the earth from each measured earth response, and creating from such impulse responses a sub-surface representation of resistivity contrasts.

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.