Airborne technology brings new hope to map shallow aquifers in Earth's driest deserts

Water scarcity is increasing across the globe. This is particularly acute in the desert regions of the Middle East, which are exposed to both extreme conditions such as drought and flooding. These uncertainties have resulted in increased reliance on shallow aquifers to alleviate shortages. However, the management of these aquifers relies on sporadic well logs, and the characteristics of these aquifers remain poorly understood.

To address this challenge, a team of researchers led by Ming Hsieh, a professor in the USC Viterbi School of Engineering's Department of Electrical and Computer Engineering, along with collaborators around the world, has developed what the team calls an “airborne sounding radar for underground desert exploration.” Developed a new prototype. Aquifer”, nicknamed “Desert-SEA”.

The new technology uses radar aboard high-altitude aircraft to map the top of an aquifer, called the water table, over an area hundreds of kilometers wide. According to researchers, Desert-SEA will measure changes in groundwater table depth at scale for the first time, allowing water scientists to assess the sustainability of these aquifers without the limitations associated with on-site mapping. He says he will do so. Harsh and inaccessible environment.

“Understanding how shallow groundwater moves horizontally and vertically is our main objective, as it helps answer several questions about the origin and evolution of groundwater in vast and harsh deserts. “These are questions that remain unanswered to date,'' says researcher Heggie. USC specializes in desert radar remote sensing and is the lead author of a paper outlining the technology. IEEE Earth Science and Remote Sensing Magazine.

How to use

This technology uses low-frequency radar to survey the ground. Radar sends a series of pulsed waves into the ground, which are reflected when they interact with water-saturated layers. From the reflected signals, the water table can be mapped with relatively high vertical and spatial resolution using a combination of arrays of advanced antennas and computational techniques.

When imaged, a stable water table typically appears as a flat reflector because the amount of water being extracted is approximately equal to the amount of water entering the system (its “refill”). However, if there is an imbalance, it will be reflected in the resulting image showing that the shape of the water table is biased upward or downward.

Similar techniques are widely used to explore ice in Antarctica and on planets. But adapting the radar to sense shallow aquifers in the desert requires solving several challenges in radar design, which he said he collaborated with industry partners in Carlsbad, Calif. It took years of hard work.

“In particular, we needed to resolve the near-surface blind zone, where highly radar-attenuating ground, unquantified noise sources, and complex clutter can obscure shallow aquifer detections. The exploration and surveying capabilities of our system exceed the exploration and surveying capabilities of commercial ground-penetrating systems.''Our system transmits a more powerful signal than any surface radar or drone-borne radar. , has a more sensitive receiver and operates several orders of magnitude faster,” Heggie said.

Current shallow groundwater maps in some regions of arid deserts, such as the Sahara, rely on data from wells tens, hundreds, or even thousands of miles apart, making it difficult to estimate groundwater volume or This can lead to inaccurate estimation of dynamics.

Heggie suggests this is like looking only at well data in New Jersey to find data on groundwater for the entire United States. (The desert regions of North Africa and the Arabian Peninsula are twice the size of the continental United States). Therefore, Heggie cautions that well logs alone cannot adequately assess their rapid evolution.

According to the researchers, Desert-SEA's ability to transmit high-power signals and use advanced onboard processing will help fill data gaps presented by the geographic distribution of well logs.

With this new prototype, Heggie predicts that even with a small plane flying at 200 miles per hour, researchers can cover in an hour what typically takes a year to cover from well log data. .

Co-author Bill Brown was the lead engineer on this project. “Desert Sea Radar represents a major advance in airborne sensing and environmental engineering,” Brown said. “By integrating high-frequency radar and AI technology, we can generate real-time, three-dimensional mapping of groundwater sources. , which is extremely important for desert oceans.” Ensuring sustainable water management in arid regions. ”

The technology will be tested in the Middle East, but it could also be broadly applied to other places experiencing long-term droughts, particularly Central Asia, Australia, and even the deserts of the United States.

This technique is most effective in very dry areas such as sand, and its particular importance goes beyond understanding current water supplies. It can also be implemented in repeated evaluations to understand agricultural sustainability and thus ensure food security for residents of these extreme environments.

“The ability to peer over arid sands and vast deserts from depths of more than 100 feet in record time allows us to answer fundamental questions about the ebb and flow of groundwater in these regions and how it is used. in a more sustainable way,” said Elizabeth Palmer, a Fulbright fellow working on the project.

“I am always happy to participate in airborne research missions, but because desert-SEA missions have the humanitarian impact of reducing water stress, it gives me a unique sense of motivation and pride. ” said Akram Amin Abdellatif, a researcher at the Institute of Technology. The University of Munich (TUM) pointed out.

The next step for the research team is to use this designed prototype to build flight models that will be implemented on helicopters and fixed-wing aircraft.