Caltech researchers have developed a groundbreaking method to measure soil moisture using seismic detectors and traffic noise. This innovative approach offers real-time data, aiding water management and conservation.
A remarkable innovation from Caltech researchers is set to transform how we measure moisture levels in soil, a crucial factor for water management and agricultural productivity. The team has harnessed seismic detectors traditionally used for earthquake monitoring to gauge soil moisture in the vadose zone — the region between the surface and underground aquifers.
Innovative Method
Caltech’s groundbreaking method pivots away from satellite imaging, which provides only low-resolution averages and cannot penetrate below the surface. Instead, the researchers leveraged vibrations from everyday activities, such as traffic, to understand moisture levels underground. These vibrations slow down when they encounter water, allowing scientists to determine moisture content with unprecedented accuracy.
Collaborative Effort
The project, a collaborative endeavor between hydrologist Xiaojing (Ruby) Fu and seismologist Zhongwen Zhan, harnesses a technique known as distributed acoustic sensing (DAS). This method utilizes lasers pointed into unused underground fiber-optic cables, transforming them into an extensive network of seismic sensors.
After a 7.2 magnitude earthquake hit Ridgecrest, California, Zhan had assembled a DAS array on a nearby cable so as to measure aftershocks. The team soon realized this setup could also track how soil moisture fluctuated over time.
Significant Findings
Over five years, the research team collected and modeled data to illustrate how vadose zone moisture varies. The study found a significant decrease in moisture in the Ridgecrest region during California’s historic drought from 2019 to 2022. Yan Yang, a graduate student in geophysics and co-first author of the study, noted the broader implications of these findings.
“From the top 20 meters of soil in the Ridgecrest region, we can extrapolate to the entire Mojave desert,” Yang said in a news release. “Our rough estimation is that every year, the Mojave vadose zone loses an amount of water equivalent to the Hoover Dam. Over the drought years of 2019 through 2022, the vadose zone has been drier and drier.”
Broader Applications
The ability to monitor soil moisture in real-time is a critical advancement for water conservation efforts. Next, the team aims to apply this technology to different regions to see how various climates affect soil moisture dynamics.
“We know this method works really well for this particular site,” Fu said in the news release. “Many other interesting regions with the same climate could have different hydrological processes, like central California, where farming operations withdraw water, but the region also receives snowmelt from the Sierra Nevada mountains.”
Support and Future Directions
This pioneering work has been funded and supported by Caltech’s Resnick Sustainability Institute (RSI) and the National Science Foundation.
“This is exactly the type of interdisciplinary, creative science that the Resnick Institute was designed to support,” added Neil Fromer, executive director of programs with RSI. “Bringing together colleagues that otherwise wouldn’t have worked together, and in that collaboration develop new tools that can help measure and manage water availability more sustainably.”
The study’s findings are detailed in the paper titled “Fiber-optic seismic sensing of vadose zone soil moisture dynamics,” published in Nature Communications. The research team includes Zhichao Shen, who is currently a postdoctoral investigator at Woods Hole Oceanographic Institution, Kyra H. Adams of the Jet Propulsion Laboratory and Ettore Biondi, a DAS scientist at Caltech.
This innovative approach holds promise not just for advancing scientific understanding but for providing actionable insights into water management and agricultural practices, potentially changing the landscape of how we monitor and utilize one of our most vital resources.