GPR can be defined as a radar whose goal is to detect and identify structures within the ground. The properties of such a radar are restricted to the frequency, bandwidth, etc., that are required to detect the desired target, either natural or man-made, in the presence of a lossy, possibly inhomogeneous medium. Propagation losses, antenna size, and size of the scatterer to be detected dictate the frequency band of operation [PDY94].
Figure 1 shows a diagram of a working GPR. A short radar
pulse is emitted at time t = 0. Immediately, the antenna starts
recording the reflected radar waves. A reflection appears at the
interface of two materials with different dielectric values
. The greater the difference 
, the
stronger is the resulting reflection. The total recording time depends
on the desired depth range. The radar signal propagates at a speed of
. A recording time of 25 ns corresponds
to approximately 1.5 meters in depth
.
When the GPR system is moved and a trace is recorded in regular intervals, a 2D image of the reflected radar waves is created. An example is Figure 7. The x-axis represents the space dimension and the y-axis is the time domain of the reflected signal, which can also be seen as the ground depth.
