ON CROSSWELL DIFFUSIVE TIME-DOMAIN ELECTROMAGNETIC TOMOGRAPHY

We investigate the reconstruction of a conductive target using crosswe ll time-domain electromagnetic tomography in the diffusive limit. The work is a natural extension of our ongoing research in the modificatio n of time-domain methods for the rugged marine mid-ocean-ridge environ ment, an environment characterized by extreme topography and pronounce d variations in crustal conductivity on all scales. We have proved bot h in theory and in practice that 'traveltime', the time taken for an e lectromagnetic signal to be identified at a receiver following a chang e of current in the transmitter, is an excellent, robust estimator of average conductivity on a path between transmitter and receiver. A sim ple estimate of the traveltime for a parallel electric dipole-dipole s ystem is the time at which the derivative of the electric field with r espect to logarithmic time at the receiver reaches its maximum. We hav e derived the fundamental relationship between the traveltime and the conductivity of the medium for a uniform whole-space. We have applied the concept of the traveltime inversion to the related crosswell probl em and demonstrated reconstructions of finite targets based on tomogra phic analyses, Results show that the crosswell time-domain electromagn etic tomography can supply useful information, such as the location an d shape of a conductive target.