Patent ID: 7957904

Claim:
A method for mapping sub-surface resistivity contrasts and checking the correctness of an intermediate step comprising: making one or more transient electromagnetic measurements in a first configuration using at least one electric source with grounded input current electrodes or at least one magnetic source with current in a wire loop or multi loop and at least one electric field or magnetic field receiver, concurrently measuring: a resultant first earth response at the at least one receiver using a known recording system, and a first true amplitude system response by measuring directly a first current in a wire at the at least one source using effectively the same recording system, using the measured first true amplitude system response to recover a first estimated earth impulse response from each measured first earth response, interchanging the at least one source and the at least one receiver to create a second configuration, making one or more transient electromagnetic measurements in the second configuration, concurrently measuring: a resultant second earth response at the at least one receiver using the known recording system, and a second true amplitude system response by measuring directly a second current in the wire at the at least one source using effectively the same recording system, using the measured second true amplitude system response to recover a second estimated earth impulse response from each measured second earth response, comparing the first and the second estimated earth impulse responses to confirm that they are identical apart from uncorrelated noise, and creating from the first and second estimated earth impulse responses a representation of sub-surface resistivity contrasts.