GPR Exploration

One of the newest geophysical methods, which today is widely used in many fields of mining exploration, is the "ground penetrating radar" method. The word radar also stands for Radio Detection And Ranging. The radar has several types.

The most important uses of GPR are:

1. In engineering geophysics, studying of the site of a dam, finding the location of the buried canals and tunnels, determining the position of probable subsidence in the road and railroad tracks, etc.
2. The environment, determining the water table and mapping contaminated areas
3. Geology and exploration of shallow mines, determining the thickness of surface soils and thickness of alluvium, determining the thickness of ice.
4. Other uses like archaeological and military studies

In this method, electromagnetic waves with different frequencies are sent to the earth and the received reflections of these waves will be analyzed. Different frequencies are produced, distributed, and received by antennas. The depth of penetration of this wave is low and depends on the electrical conductivity of the earth and the frequency used. 

In general, the greater the electrical conductivity of the earth is (such as in shale and clay environments), the lower the depth of penetration will be, and the less the electrical conductivity of the earth is (such as in calcareous and dry environments), the depth of penetration will be greater. Also, the higher the frequency is, the lower the penetration depth will be.

When the electromagnetic pulse emitted from the antenna hits an electrical discontinuity, a part of it will be absorbed and the rest of it will be reflected. This is due to the change in the electromagnetic impedance in the intersection. The amount of reflected and transmitted energy, as well as the amount of lost energy, depends on the electrical properties of the material on both sides of the intersection. If we calculate the sweep time of the electromagnetic wave, which is emitted from the transmitter's antenna and then is reflected from the reflective mass to the receiver antenna, we can determine the depth of the target mass. This is possible if the electromagnetic pulse rate is specified in the environment. 

GPR antennas do not emit only a single pulse. They emulate a number of specific pulses at specified intervals, usually between 2 and 50 μs.

Sampling in the GPR method is related to the sampling time interval between the two successive pulses.

In addition to the frequency of the antenna, other important parameters in the sampling include the time interval, distance between the stations, the position of the sampling profiles, the selection of sampling distances on the recorded waveform. This parameter is controlled by the Nyquist theory. According to this theory, the frequency of sampling should be at least 10 times grater than the initial frequency of the antenna.