What’s Beneath the Surface of Ground-Penetrating Radar?July 01, 2020 by Kayla Matthews
Ground-penetrating radar helps unearth the splendors of ancient civilizations. But what's beneath the surface of these complex electronic devices?
One of the most fascinating things about modern engineering advancements is that researchers can use them to learn about ancient civilizations. Take the recent example of surveyors using ground-penetrating radar (GPR) to map a Roman city called Falerii Novi, founded in 241 B.C. The team relied on GPR to see the details of buried buildings without digging.
GPR indicated that some of the walls around Falerii Novi fell victim to stone robbing. Image used courtesy of L. Verdonck and the University of Cambridge
LiDAR (light detection and ranging) technology has also come into play with new archeological discoveries. One recent example involved finding a 3,000-year-old Mayan ceremonial site.
These examples show that there are new and exciting ways to learn more about the past. Here, we'll take a close look at the first technology mentioned above—GPR.
What Is Ground-Penetrating Radar?
Ground-penetrating radar, or GPR, is a non-destructive method of using electromagnetic fields to take images of subsurface materials. It relies on radio frequencies within the microwave band of the radio spectrum.
GPR sends small energy pulses into a material and measures the return time and strength of the reflected signal. Image used courtesy of GSSI
Researchers slowly move their equipment over the desired area to study, sometimes using a wheeled platform containing the equipment that looks a bit like a lawnmower. They end up with a cross-sectional image of subsurface objects.
How Does Ground-Penetrating Radar Work?
What exactly is beneath the surface of these devices, though? This approach requires a GPR transmitter and an antenna to send a high-frequency radio signal into the ground.
Once that signal collides with a buried object, it becomes reflected, refracted, or scattered back to the surface. Next, a receiving antenna tracks how the returned signal varies from the one sent out.
Researchers store the data from the receiving antenna in a digital format. A computer can then analyze that information by measuring how long it takes for a radio wave pulse to travel to and from its target.
Learning that information tells researchers the depth and location of an underground object. The antennas used in GPR measurement system are exceptionally important because they transmit and receive waves at the right level and frequencies.
GPR applications and frequencies. Image used courtesy of Sensors and Software
GPR measuring equipment includes a screen that helps researchers view and interpret the data. They see the information as images or graphs and require training to assess them accurately.
For example, GPR waves can penetrate a variety of materials, including soil and concrete. Factors such as the amount of water saturation and the conductive properties of the material affect the GPR waves and how the data appears.
The Main Parts of a GPR System
As an electrical engineer, you may help design GPR systems from scratch or make improvements to an existing model. Let's go over the parts of GPR equipment and the functions they serve.
This part has electronics to trigger the radar pulse that the antenna transmits into the ground. The control unit also has an integrated computer and digital memory system to hold the collected data for later examination. After getting information from a receiving antenna, the control unit shows it as a computerized chart.
Some control units on the market connect to a laptop computer containing specialized software. This setup facilitates more streamlined data processing and interpretation because it eliminates the step of transferring the data from the receiving antenna onto another machine.
The transmitting antenna sits at or near the ground level on the site chosen for analysis. Researchers must choose antennas of particular frequencies depending on how far into the ground they want to go. Higher-frequency antennas do not go as deeply into the ground as lower-frequency options. However, higher-frequency choices detect comparatively smaller objects.
Ground-penetrating radar technology. Image used courtesy of GSSI
Once an antenna gets the pulse from the control unit, it amplifies it and sends it into the ground at a certain frequency. Radar waves occur by directing high voltage near the middle of a copper plate while sending regulated pulses of energy. The electromagnetic field forms around the copper plate as current continuously goes from the center of the plate to its edges.
The receiving antenna captures the radio wave data sent up from the ground. The transmitting and receiving antennas must sit at the correct distance from each other. Having them too close together may distort the received data. That issue occurs because of the resonance of the copper plate associated with the transmitting antenna.
Ground-penetrating equipment requires a power source. Batteries are popular due to their portability. Some models use rechargeables or automobile batteries. However, others work with external 110/220-volt energy sources.
The Future of Ground-Penetrating Radar
Ground-penetrating radar offers a diverse assortment of possible uses. For instance, this technology is currently being used in a project to excavate a buried Viking ship in Norway. Other possibilities will arise as more electronic innovations are forged in this field.
Have you ever worked with GPR? What can you tell us about your hands-on experience with its circuitry? Share your experiences in the comments below.