Methods
GPR / Ground Penetrating Radar
This method involves transmitting electromagnetic pulses of energy at microwave frequencies into the ground and measuring the travel times and amplitude of the returned signals.
The physical properties of the subsurface environment that are relevant for this method are the electrical conductivity and the dielectric properties. The dielectric properties determine the velocity of the electromagnetic wave. The conductivity is extremely important because it determines the rate of signal attenuation. Objects characterized by high conductivity cause rapid dissemination of the transmitted pulse through the transformation of the electromagnetic energy into heat (similar to the effect of the microwave oven).
The antennas used for GPR surveys have to be selected depending on the depth of investigation and the size of the target of investigation. The frequency varies inversely with the depth of investigation, and directly with the size of the target of investigation. Therefore, as resolution and the accuracy of the data increase, the of investigation is reduced.
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The picture to the left shows the layers of a road that has been scanned usig a GPR system. |
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