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Gpr Attenuation Tomography For Detecting DnaplsNormal access

Authors: Lanbo Liu and Youli Quan
Event name: 10th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
Session: Environmental Site Assessment
Publication date: 23 March 1997
Organisations: EEGS
Language: English
Info: Extended abstract, PDF ( 814.54Kb )

Using the ground penetrating radar (GPR) to detect organic contaminants in the geological
formations is a relatively new technique for environmental site characterization. We present here an
attenuation tomography method that could be used to image subsurface organic contaminants like
DNAPLs. This method is based on centroid frequency shift when the electromagnetic (EM) waves
propagate in subsurface media. In most natural materials, EM wave attenuation increases with
frequency. As a result, the centroid of the signal’s spectrum experiences a downshift during
propagation. This downshift is proportional to a path integral through the attenuation distribution
and can be applied to the GPR data to tomographically reconstruct the attenuation distribution. The
frequency shift method is applicable to any data when the signal bandwidth is broad enough and
the attenuation is high enough to cause noticeable losses of high frequencies during propagation. In
comparison to some other methods of estimating attenuation, the frequency shift method is
relatively insensitive to geometric spreading, reflection effect, source and receiver coupling,
radiation patterns, and instrument responses. High attenuation has been regarded as the major
hurdle for using GPR in areas with high electric conductivity, this method provides an alternative
view to the attenuation.

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