scholarly journals Fast evaluation of zero-offset Green's function for layered media with application to ground-penetrating radar

2007 ◽  
Vol 34 (21) ◽  
Author(s):  
Sébastien Lambot ◽  
Evert Slob ◽  
Harry Vereecken
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Ground Penetrating Radar ◽  
Layered Media ◽  
Fast Evaluation ◽  
Zero Offset ◽  
Ground Penetrating

Efficient loop antenna modeling for zero-offset, off-ground electromagnetic induction in multilayered media

Geophysics ◽  
2010 ◽  
Vol 75 (4) ◽  
pp. WA125-WA134 ◽  
Author(s):  
Davood Moghadas ◽  
Frédéric André ◽  
Harry Vereecken ◽  
Sébastien Lambot
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Electromagnetic Induction ◽  
Dynamic Range ◽  
Transfer Functions ◽  
Signal To Noise Ratio ◽  
Loop Antenna ◽  
Multilayered Media ◽  
Fast Evaluation ◽  
Zero Offset

Retrieval of the subsurface electrical properties from electromagnetic induction (EMI) data using inverse modeling relies in particular on the accuracy of the considered EMI model. We have developed a new EMI approach whereby a zero-offset, off-ground loop antenna is efficiently modeled using frequency-dependent, complex linear transfer functions and the air subsurface is described by a Green’s function for wave propagation in 3D multilayered media. To ensure proper calibration of the system, vector network analyzer (VNA) technology is used as the transmitter and receiver. An optimal integration path is proposed for fast evaluation of the spatial Green’s function from its spectral counterpart. We validated the antenna model in laboratory conditions with measurements performed with a loop antenna in free space and at different heights above a perfect electrical conductor. Provided that the loop antenna is high enough above the reflector (off-ground condition), the measured and modeled Green’s functions agreed remarkably well. In addition, inversion of the EMI data resulted in accurate estimates of the antenna heights. Yet, as expected, signal-to-noise-ratio issues occurred for the higher antenna heights and frequencies away from the loop resonant frequency. The method appears to be promising for accurate and robust soil characterization, but needs high VNA dynamic range and antenna gain.

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