The Ground Penetrating Radar (GPR) method is comparable to the reflection seismic method.

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  Step 1: Outcrop
  Figure shows a photography of the outcrop. We can see different channels with change in grain sizes. These layers were deposited during floods of the river (la Bruche). Along few meters these channels show drastic changes in size and thickness.
  The top of the water table is situated at a depth of 6 m from the ground surface.


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  Steps 2 to 4: Imaging with different frequencies
  The images were obtained from constant offset sections recorded with a Pulse EKKO radar emitting an electromagnetic pulse with different central frequencies of 50, 100 and 200 MHz. The source antenna – receiver antenna distance is 1 m.
  On the GPR sections, the top of the water table is at 90 ns. A simple processing sequence is applied to the data sets. It includes a low-cut frequency filter to cancel the very low frequency component of the electromagnetic signal and a gain function to highlight electromagnetic impedance contrasts. Furthermore, a time delay correction has been applied on the 50 MHz section to put the maximum of the first phase of the electromagnetic signal at the same time as the time observed on the 100 MHz section.
  We can observe that on the 100 and 200 MHz sections, we have a much better vertical resolution which allows the identification of reflected waves. In particular, the reflected wave associated with the water table can be clearly seen at 90 ns on the 200 MHz section.


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  Step 2: 50 MHz section


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  Step 3: 100 MHz section


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  Step 4: 200 MHz section

Reference

JF Girard, 2002, Ground Penetrating Radar, Imagerie géoradar et modélisation des diffractions multiples, PhD.- Thesis à l’université de Strasbourg I.,
http://tel.archives-ouvertes.fr/tel-00135945/fr/