GEORADAR
The electromagnetic pulse radar is a complex and technologically advanced system capable of probing the ground with remarkable detail to depths of approximately 131.234 feet, depending on multiple factors.
The results of the research work represent vertical cross-sections of the subsurface, allowing the identification of the presence of metallic materials, cement foundations, pipes, cables, cavities, liquid leaks, stratigraphic reconstructions, and anomalies in general.
The radar consists of a broadband electromagnetic pulse transmitter and its corresponding receiver.
The radar is composed by:
- MAIN UNIT SIR-SYSTEM
- VARIOUS ANTENNAS (from 80 MHz to 2.6 GHz)
In general, electromagnetic waves have the ability to travel both through air and in a material medium; in our case, the main object of the research is the ground. What changes, broadly speaking, is the propagation speed, being in the air equal to the speed of light and in a material medium equal to the ratio between the speed of light and the square root of the dielectric of the medium.
The wave is transmitted to the ground by means of a transmitting antenna, and the reflected waves in the ground received by a receiving antenna. In practice, most antennas are manufactured by installing the receiving and transmitting units in the same module. The signal sent to the antenna from the transmitter is a pulse of limited duration, and the listening time of the system is selected based on the study’s objectives.
The choice of antenna to be used depends on the investigation’s objective and the electrical parameters of the ground, such as electrical conductivity and magnetic permeability. The radar signal penetration depth depends on several factors, the most important being:
- The conductivity of subsurface materials; greater penetration is achieved in resistive media than in conductive ones.
- The emission frequency; penetration is inversely proportional to frequency.
Part of the energy transmitted by the antenna will be reflected by underground objects or by geological discontinuities if present, and will be received by the receiver.
The energy of the reflected pulse will be directly proportional to the contrast in the value of the physical parameters between the underground object and the surrounding ground. The radar measures time, and to obtain depths, in distance units, of observed anomalies, a time/depth conversion must be carried out through:
- The correct selection of the subsurface’s electrical parameters.
- A direct calibration borehole.
- Specific calibration for antennas that move at a certain height above the ground.
In practice, the study is conducted as follows:
- Moving the transmitting-receiving antenna in contact with the surface to be investigated.
- Moving the transmitting-receiving antenna at a certain distance, height, from the surface to be investigated. This applies to Horn antennas, "air cushion," used for detailed pavement investigations.
- In all cases, a survey grid is designed based on the work's object.
The acquisition system is transported by an appropriate vehicle and connected to the antenna via a communication cable.
The system provides an interpretable profile in acquisition mode and stores the data digitally (32 bits) to allow, if necessary, the application of different filters to facilitate interpretation. As compared to other available geophysical techniques, GPR survey has the following advantages:
- Speed of surveying. Immediately after the acquisition phase, it is possible to evaluate the nature, structure, and thicknesses of the subsurface.
- Non-destructive investigation. The ground is not altered by any excavation or drilling.
- Capability to conduct quasi-continuous studies. This avoids the interpolation of geophysical data and its possible errors.
- The method can be applied not only to soils but also to surfaces covered by ice and fresh water.
Examples of ground-penetrating radar applications
Contamination
Large diameters
3-inch Pipes
4-inch Pipes
6-inch Pipes
Other pipes
