From Notre Dame to Mars, Ground-Penetrating Radar Unearths Mysteries Previously Unseen
How are ground-penetrating radars forging exploration in space exploration, archeology, explosive detection? It turns out, this technology can be quite versatile.
When AAC contributor Johnathan Powell first covered ground-penetrating radar (GPR) a few years ago, he highlighted how the technology helped researchers uncover details of a lost Maya city that had been buried beneath jungle foliage for centuries.
An Archeologist at the Maya Head of Stone site, which was brought into focus with GPR. Image used courtesy of Michael G. Callaghann
Since that time, researchers have put GPR to use in dozens of other use cases, ranging from Mars exploration to fiber optic installation. But this technology is not without its limitations, both in system design and implementation.
In our last article on ground-penetrating radar, we discussed the basics: what it is, the main parts of the system, and how it works. Now, we'll cover some of the challenges of working with this technology and the manifold ways it continues to make headlines.
The Main Limitation of GPR: Materials
Even a GPR system designed to the highest standards may not provide the desired performance level in certain conditions. Knowing about the desired usage environment will help GPR users to determine if this technology is the right method to use for a particular exploratory project.
The main shortcomings associated with GPR relate to material types, according to researchers from Keele University. For example, radio waves do not transmit well through metal, clay-rich soils, and saline. Additionally, the quality of received data depends on the correct positioning between the two antennas, as well as choosing an antenna that gives off the right frequency for the depth you want.
GPR works by sending electromagnetic energy into the ground by the transmitter antenna and reflecting it back to the receiver. Image used courtesy of Keele University
Dealing with antenna placement and type is easier once you become more acquainted with the needs of a particular ground-penetrating radar project. However, getting around the issues associated with material characteristics is not as straightforward and may require alternative methods.
How Do People Use GPR?
Despite some of the challenges of GPR, both in its system design and hands-on usage, this system is the linchpin of several exploration projects—some that are literally out of this world.
Back in 2003, researchers chose GPR to help them prepare for a subsurface exploration of Mars. The researchers compiled all the basic off-the-shelf components for the transmitter and receiver subsystems—including RF and digital ICs, connectorized components, and evaluation boards.
The transmitter and receiver equipment. Image used courtesy of Leuschen, et. al
They then took their prototype to Mars-like landscapes for field experiments in Kansas and Alaska. From their efforts, they were able to use GPR to assess "near‐surface thaw, discontinuous permafrost, water‐saturated soils, and lenses of pure ice." This experiment will help them further refine GPR to eventually send to Mars for subsurface exploration.
Many researchers rely on computer vision to process data gathered by ground-penetrating radar. One research group from Duke used GPR and machine vision in tandem to categorize a subsurface object as explosive or nonexplosive. The virtues of GPR in this use case was the system's sensitivity to non-metallic disturbance underground, allowing it to play nicely with EMI sensing, which does not pick up on low-metal or non-metal explosives as easily.
In this instance, researchers put statistical learning algorithms to work in the hopes of cutting the rate of false alarms.
More recently, MIT researchers applied GPR to self-driving cars. Even the most advanced models under development struggle in wet or snowy conditions that affect the sensing ability of the LiDAR or cameras. Scientists think GPR could help cars navigate in adverse conditions.
Self-driving vehicle totes GPR equipment through the snow to assess the ground conditions. Image used courtesy of MIT
The automobiles still require other sensors, but GPR would complement those. The team successfully used GPR in this way on a closed road at low speeds.
Engineers in the United Kingdom chose GPR to assist with the expansion of a fiber-optic network. Doing this cuts costs and shortens disruption time by showing workers precisely where to dig the new cables. The telecom company behind the project prefers to utilize existing infrastructure when possible.
GPR can show the current below-ground structure, helping workers proceed more efficiently.
Another project used GPR to survey nearly two acres of a Florida country club. Analysts found 40 subsurface anomalies they believed to be two or three rows of unmarked graves. The scientists backed up their suspicions by using a pair of dogs trained to detect human remains.
The land occupied by the country club was once a plantation where the approximately 80 enslaved peoples lived. The graves may be the resting places of some of those peoples.
Researchers from the Laboratoire de Recherche des Monuments Historiques (LRMH) plan the first study of its kind to probe beneath the foundation of the famous Notre Dame Cathedral. Restoration work is underway after a fire nearly destroyed the landmark in April 2019. Multiple researchers are working to learn more about the religious site.
What's under Notre Dame? Researchers are using GPR to find out amidst the restoration project. Image used courtesy of Christa Lesté-Lasserre
GPR may confirm the beliefs of some scholars that the site contained other worship buildings first.
More Exploration to Come
There is an increasing number of ground-penetrating radar manufacturers, and that number is expected to grow throughout 2020, according to a MarketWatch report. With this high demand, we'll likely see more innovations in GPR at the system level and consequentially, even more fruitful use cases to come.
Featured image (modified) used courtesy of Science Magazine
Does your passion for a design project ever vary based on its intended application? Or do you find plenty of fulfillment from the design process in and of itself—regardless of where it'll end up? Share your thoughts in the comments below.