Georadar

The Georadar technique has a multitude of practical applications in many fields of research  (geology, engineering, architecture, environment, restoration, excavations, archaeology, etc…). Below we mention some of the applications:

• Determination of the state of foundations of structures, buildings, bridges,…
• Determination of the state of conservation of building facades.
• determination of different subsoil lithologies, depth and geometry.
• Location of cracks, fractures in the rock.
• Determination of subsoil contaminants, hydrocarbons,…
• Location of services and buried artificial structures (pipes, tanks,…)
• Location of cavities in the subsoil.

The Geo radar or GPR (Ground Probing Radar) method produces continuous high-resolution profiles similar to those produced by reflection seismic. The main advantages of this technique are the speed of data acquisition (each measurement point or trace is taken in a few seconds), the versatility in terms of system layout due to the possibility of exchanging antennas of different frequencies and the parameters of the electromagnetic wave, and its non-destructive character .

The main disadvantage is the excessive dependence on the characteristics of the terrain to which it is applied, due to certain circumstances that attenuate the penetration of the electromagnetic impulse (such as the existence of high clay and/or humidity contents), and therefore, the detectability of subsoil structures. Conductivity produces a decrease in impulse energy, therefore, the greater the conductivity, the greater the attenuation that occurs.

The physical principle of the method used consists of the fact that subsurface radar equipment radiates short pulses of radio-frequency electromagnetic energy to the subsurface through a transmitting antenna. When the radiated wave encounters heterogeneities in the electrical properties of ground materials, determined mainly by the content of water, dissolved minerals, expansive clays and heavy minerals, part of the energy is reflected back to the surface and part is transmitted to greater depths. . The emission, transmission, reflection and diffraction of radar waves is defined by Maxwell’s equations.

The reflected signal is amplified, transformed into the audio-frequency spectrum, recorded, processed and printed. The record shows a continuous profile indicating the total travel time of a signal as it passes through the subsurface, reflects off a heterogeneity, and returns to the surface. This double trip (TWT – Two Way Time) is measured in nanoseconds (1 ns= 10-9 seconds).

The selection of the frequency of the antennas for a given study is a function of the compromise between resolution and penetration, so that high frequencies are more resolving at shallow depths, while low frequencies are more penetrating with lower resolution. For the present study, 100 MHz central frequency antennas have been used to obtain maximum resolution with a penetration greater than five meters, taking into account the clay nature of the subsoil.

The digital signal of the radar waves has been recorded in the form of a binary file using a laptop computer, which facilitates its subsequent computer processing. To improve the representation of the results, different numerical filters and signal amplifiers have been used, according to the needs of the research.