HR: 16:20h
AN: NS34A-04 INVITED     [Abstracts]
TI: New developments in high-resolution multicomponent georadar imaging
AU: * Streich, R
EM: streich@aug.ig.erdw.ethz.ch
AF: Swiss Federal Institute of Technology, Institute of Geophysics, ETH-Hoenggerberg, CH-8093 Zurich, Switzerland
AU: van der Kruk, J
AF: Swiss Federal Institute of Technology, Institute of Geophysics, ETH-Hoenggerberg, CH-8093 Zurich, Switzerland
AU: Green, A G
AF: Swiss Federal Institute of Technology, Institute of Geophysics, ETH-Hoenggerberg, CH-8093 Zurich, Switzerland
AB: Scalar imaging algorithms originally developed for processing seismic reflection or remote sensing data are commonly used for imaging georadar data. Unfortunately, such algorithms do not account for the radiation characteristics of georadar antennas and the vectorial nature of radar waves. Consequently, georadar images obtained from such algorithms are often not optimally focused, exhibiting the effects of antenna radiation and wave propagation. Multicomponent imaging is a viable technique for taking into account the electromagnetic properties of georadar data, but it therefore requires measuring two components of the electric field. In a three-dimensional (3-D) high-resolution multicomponent survey, it is crucial to measure trace positions precisely while maintaining survey efficiency. We achieve this by linking a multichannel georadar system to a high-quality differential GPS unit. This setup allows us to record two components of the electric field and accurate position information simultaneously, without the need to adhere to a fixed grid during the survey. Using this setup, we have collected two pairs of co- and cross-polarized 3-D data sets on a 40x40~m area in a braided river environment. The relative trace positions obtained after post-processing the GPS data were mostly accurate to ±0.1~m. From these data, we derived two independent multicomponent 3-D images. Our original multicomponent imaging algorithm was based on far-field approximations of the radiation patterns for infinitesimal dipole antennas. To describe the effects of wave propagation more accurately, we have extended the multicomponent imaging algorithm to take into account the total antenna radiation characteristics and antennas of finite length. This should result in more accurate images, especially for the dipping, quasi-planar structures that dominate our data. Computational efficiency has previously been a major problem that inhibited using the total antenna radiation characteristics. Our new implementation is reasonably efficient, because it is based on wavenumber-frequency domain formulations of the Green's functions that describe directional antenna radiation and wave propagation. We thus avoid evaluating the corresponding space-frequency domain integral expressions of the Green's functions. The performance of the new total-field imaging operator has been tested on finite-difference time-domain modeled data containing variously oriented dipping reflectors. Compared to far-field images, the total-field images of these synthetic data show superior amplitude and phase (i.e., location) consistency of the imaged reflectors. An analysis of the total-field images obtained from the braided river field data and comparison with the corresponding far-field images revealed similar enhancements of the image quality. These results indicate that total-field multicomponent imaging of georadar data can increase our confidence in the interpretations of reflector locations and reflection amplitudes.
DE: 0604 Antenna arrays
DE: 0629 Inverse scattering
DE: 0644 Numerical methods
DE: 0694 Instrumentation and techniques
DE: 0699 General or miscellaneous
SC: Near-Surface Geophysics [NS]
MN: 2005 Joint Assembly