Electromagnetic Imaging (EMI) is an extremely low frequency version of Ground Penetrating Radar (GPR) that provides deep non-invasive imaging of the subsurface. Recent breakthroughs in low frequency time-domain modeling show that reflections from frequencies in the very low megahertz range (center-band frequencies down to 500 kHz). Simulations of EMI data facilitate an understanding of the effects of complex electromagnetic phenomena in the intermediate frequency range (1-50 MHz) where both conduction and displacement currents affect wave propagation, as well as predicting the performance of radar antennas over a complex heterogeneous subsurface geologic environment. Our results show that specular reflections from objects buried down to a depth of 15-20 m in a heterogeneous environment can be imaged using a robust finite difference time domain algorithm (FDTD) with a source pulse center-band frequency lower than 1 MHz. A highly efficient robust algorithm was developed to enhance the effectiveness of the simulation in surroundings characterized by an arbitrary distribution of all electromagnetic properties (conductivity, permittivity, and permeability). The modeling is facilitated by a graphical algorithm that enables a detailed simulation of each component of the system, including a heterogeneous half-space and the physical details of the transmitter and receiver antennas. In terms of specific targets, the results produced by the simulation demonstrated the applicability of low frequency GPR for detecting cavities in heterogeneous environment down to depths of 20 m using 500 KHz center-band source pulse.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 0619 Electromagnetic theory;
- 0634 Measurement and standards;
- 0659 Random media and rough surfaces