Baseball scouts use it to measure pitch velocity in hopes of discovering the next Aroldis Chapman or Nolan Ryan. Tom Cruise used it in “Top Gun” to evade enemy fighters. Police use it to catch speeders.
And Mahta Moghaddam — an internationally renowned researcher and the William M. Hogue Professor of Electrical and Computer Engineering at USC Viterbi— uses it to peer beneath the Earth’s surface.
It’s radar, which determines the presence and location of objects by sending out radio waves and measuring how long they take to bounce back, how strongly, and from what direction.
Now Moghaddam and her pioneering radar work are helping scientists better understand climate change and its serious consequences.
In recent years, NASA has used her P-Band radar system and ground sensors as part of the Arctic-Boreal Vulnerability Experiment, or ABoVE, a massive, 10-year effort to monitor shifts in Arctic and boreal ecosystems. Moghaddam and members of the Microwave Systems, Sensors and Imaging Lab (MiXIL) she directs have also employed P-Band in arid Arizona and central California to measure soil moisture beneath the dry surface — information that could one day reduce farmers’ water use. A closely related project could make it possible to outfit relatively inexpensive drones with radar technology to map or even discover aquifers.
“The planet is in trouble right now. There’s a lot of evidence that the climate is changing, temperatures are going up, and there are various repercussions that are happening,” said Moghaddam, a 2019 National Academy of Engineering inductee whose research includes using microwave technology to retrieve information about the Earth’s surface and subsurface and to target and treat breast cancer, among many other applications. “So the Earth needs help.”
For tens of thousands of years, permafrost has trapped vast amounts of carbon in layers of frozen soil up to a mile thick. The Arctic permafrost is believed to hold roughly double the amount of carbon there is in the Earth’s atmosphere.
Climate change, however, now threatens to wreak havoc on much of the planet’s permafrost, which covers nearly one-quarter of the Northern Hemisphere. A 2017 report by the Arctic Council found that near-surface permafrost has warmed more than .5 degrees Celsius in little more than a decade. As the permafrost thaws, once-frozen plants, animals and other organic matter decompose and release greenhouse gases such as carbon dioxide and methane into the atmosphere. In Alaska, some roads built on now-melting permafrost have sunk, and bridges have become unstable.
“The concern is that thawing permafrost will create more CO2 than growing vegetation takes in and will contribute to global warming,” said Peter Griffith, managing director of ABoVE and director of NASA’s Carbon Cycle and Ecosystems Office. “It’s a vicious cycle.”
Until ABoVE, scientists had relatively limited data on climate change’s impact on permafrost in Alaska and northwestern Canada. Launched in 2016, the decade-long, $100 million-plus NASA-led effort aims to answer macro-environmental questions about the region, including the climate’s impact on permafrost thawing; the exchange of gases between land and the atmosphere; and the effect on the region’s wildlife habitat. To date, 731 scientists from around the globe have worked on ABoVE, Griffith said.
Moghaddam has made several important contributions to the project.
She came up with the P-Band radar observation concept that measures the depth of the ice-rich soil that sits above the permafrost as well as the top layer of permafrost. Attached to NASA’s Gulfstream III aircraft, the low-frequency radar — built by the Jet Propulsion Laboratory — operates at wavelengths long enough to penetrate the soil, vegetation and ground. “It’s kind of magical,” Moghaddam said.
ABoVE flights outfitted with P-Band in 2017, along with NASA test flights that employed it in 2014 and 2015, helped confirm long-held suspicions that the permafrost is indeed thawing in some parts of Alaska and Canada. Additionally, ground sensors installed in Alaska by Moghaddam and others have continuously provided ABoVE researchers with important information about soil moisture and temperature.
“Mahta’s been a leader on the science team in the use of radar to help us scale what we know is happening on a site basis across landscapes,” Griffith said. “She’s also contributed as a technological innovator.”
Peering Beneath the Surface
Sunbaked for most of the year, large swaths of Arizona and California’s Central Valley would seem bone dry. But dig beneath the surface — literally. That’s what Moghaddam and her team have done at three sites in Walnut Gulch, just outside Tucson.
The researchers have placed hundreds of sensors in Arizona as well as at five sites in central California and one in upstate New York. The sensor networks, built from scratch, measure water content in the soil and constantly transmit information to Moghaddam’s lab back in Los Angeles.
To gain a more complete picture, NASA aircraft have flown the P-Band radar over these areas to map soil content at various depths, including where the roots of plants reside. (Hardy farmers raise crops in some of these fertile but thirsty lands.)
Moghaddam hopes that hydrologists, ecologists, and climate modelers can put this information to good use.
“These are the people who actually have large-scale models of the globe. These are the people who say, for instance, that in 10 years the average temperature is going up by x degrees,” she said. “However, their predictions are no better than the data that go into them. So if you give them good information, you get much better information out.”
Farmers could also benefit from Moghaddam’s radar and sensor research on soil dampness in harsh climes. They might, for instance, discover that their parched farmland actually contains more water just beneath the surface than originally thought. The possible result: less wasted water and more conservation.
Swarming for Water
Despite its many uses, the P-Band radar has limitations. The low-frequency radar can peer only about two feet into the soil. With that in mind, Moghaddam and her researchers have set about creating a modified P-Band radar with an expanded frequency range, higher resolution, and the ability to look as much as 20 feet beneath the surface.
They have made considerable progress.
She and researchers from MiXIL are working on software-defined radar (SDRadar) that would greatly expand P-Band’s bandwidth of 420 to 440 megahertz to between 300 megahertz and 3 gigahertz, enabling the system to produce higher-resolution maps. Additionally, they are creating software, firmware and “synthetic ultra-wideband algorithms” that would make it possible for such advanced technology to fly on low-cost drones. “That way, we won’t need a huge, expensive airplane, except to map very, very large areas,” Moghaddam said.
Sam Prager, an electrical and computer engineering Ph.D. student in Moghaddam’s lab, called their SDRadar “super flexible,” with myriad uses.
“It could provide an additional level of validation of P-Band radar data; map aquifers and subglacial lakes; and be used to discover new water sources much more affordably than existing methods. And these radar sensors in the future might help detect landmines,” he said.
Moghaddam’s team, Prager added, is working on developing swarms of drones that would “work together to get higher resolution and image deeper than any of them could do alone.” Toward that end, Prager and other MiXIL researchers aim to synchronize the drones’ actions to within trillionths of a second.
SDRadar sensors have already performed well in several experiments. They have successfully imaged landmines; measured the water table depth in parts of the Mojave Desert; and looked at the snow depth and imaged snow and ice layers in Mammoth Lakes, California — information experts could one day use to predict the likelihood of avalanches, Prager said.
Reflecting on her decades-long radar and sensor research, Moghaddam said she hopes to make a difference.
“As an engineer and citizen of the world, I do believe we must use our abilities to the best that we can to benefit humanity,” she said.