9. Shallow/Near-Surface Structural Applications -Invited-
A Finite-difference, Discrete-wavenumber Method for Calculating Radar Traces
Karl J. Ellefsen(1), Aldo T. Mazzella(2), Craig W. Moulton(1) and Jeffrey E. Lucius(1)
(1) U.S. Geological Survey, USA. (2) U.S. Environmental Protection Agency, USA.
Abstract
A hybrid of the finite-difference method and the discrete-wavenumber method is developed to calculate radar traces for forward modeling and waveform inversion. The method is based on a three-dimensional model defined in the Cartesian coordinate system; the electromagnetic properties of the model are symmetric with respect to a vertical plane. Wave propagation within the vertical plane is simulated with the finite-difference method, and wave propagation outside the vertical plane with the discrete wavenumber method. Although this hybrid method is more complex than a three-dimensional implementation of the finite-difference method, it requires significantly less computer time and memory. Radar traces calculated with this method are compared to traces recorded between two boreholes in a laboratory tank. The calculated traces include direct, reflected, and head waves that are seen also in the recorded traces; in other words, the calculated and recorded traces are practically identical. Likewise, traces calculated with this method are practically identical to traces recorded in a laboratory cell using surface radar. These comparisons indicate that this hybrid method is suitable for forward modeling of both crosswell and surface radar data. This hybrid method can simulate wave propagation in a model with complex heterogeneity, and so it is suitable for imaging heterogeneity within the near-surface using waveform inversion.
Last modified: Wed May 10 23:48:53 2006