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Abstract

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

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/content/papers/10.3997/2214-4609-pdb.204.1997_025
1997-03-23
2020-08-06
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http://instance.metastore.ingenta.com/content/papers/10.3997/2214-4609-pdb.204.1997_025
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