ELECTROMAGNETIC VELOCITY INVERSION USING 2-D MAXWELLS EQUATIONS

We adapt the wave-equation traveltime inversion (WT) method to the rec onstruction of the dielectric distribution from crosswell radar travel time data. The data misfit gradient is computed using finite-differenc e solutions to the 2-D Maxwell's equations. An advantage of the wave-e quation method over ray-tracing radar tomography is that it accounts f or scattering and diffusion effects and works well in both resistive a nd moderately conductive rocks. Comparisons with ray-tracing tomograph y show that the wave equation method is more robust and accurate when the rock conductivity is larger than .002 S/m. The methods are about e qually effective when the conductivity is less than or equal to .001 S /m. The major disadvantage of the wave equation scheme is that it gene rally requires at least several orders of magnitude more computational time than ray tracing. We also derive the general equation for the wa veform radar inversion method, which is closely related to the equatio ns for the WT method and prestack radar migration.