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By NASA
Earth (ESD) Earth Explore Explore Earth Science Climate Change Air Quality Science in Action Multimedia Image Collections Videos Data For Researchers About Us 6 Min Read NASA Uses Advanced Radar to Track Groundwater in California
The Friant-Kern Canal supports water management in California’s San Joaquin Valley. A new airborne campaign is using NASA radar technology to understand how snowmelt replenishes groundwater in the area. Credits:
Bureau of Reclamation Where California’s towering Sierra Nevada surrender to the sprawling San Joaquin Valley, a high-stakes detective story is unfolding. The culprit isn’t a person but a process: the mysterious journey of snowmelt as it travels underground to replenish depleted groundwater reserves.
The investigator is a NASA jet equipped with radar technology so sensitive it can detect ground movements thinner than a nickel. The work could unlock solutions to one of the American West’s most pressing water challenges — preventing groundwater supplies from running dry.
“NASA’s technology has the potential to give us unprecedented precision in measuring where snowmelt is recharging groundwater,” said Erin Urquhart, program manager for NASA’s Earth Action Water Resources program at NASA Headquarters in Washington. “This information is vital for farmers, water managers, and policymakers trying to make the best possible decisions to protect water supplies for agriculture and communities.”
Tracking Water Beneath the Surface
In late February, a NASA aircraft equipped with Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) conducted the first of six flights planned for this year, passing over a roughly 25-mile stretch of the Tulare Basin in the San Joaquin Valley, where foothills meet farmland. It’s a zone experts think holds a key to maintaining water supplies for one of America’s most productive agricultural regions.
Much of the San Joaquin Valley’s groundwater comes from the melting of Sierra Nevada snow. “For generations, we’ve been managing water in California without truly knowing where that meltwater seeps underground and replenishes groundwater,” said Stanford University geophysicist and professor Rosemary Knight, who is leading the research.
This image from the MODIS instrument on NASA’s Terra satellite, captured on March 8, 2025, shows the Tulare Basin area in Southern California, where foothills meet farmlands. The region is a crucial area for groundwater recharge efforts aimed at making the most of the state’s water resources. Credits: NASA Earth Observatory image by Michala Garrison, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. The process is largely invisible — moisture filtering through rock and sediment, and vanishing beneath orchards and fields. But as the liquid moves downhill, it follows a pattern. Water flows into rivers and streams, some of it eventually seeping underground at the valley’s edge or as the waterways spread into the valley. As the water moves through the ground, it can create slight pressure that in turn pushes the surface upward. The movement is imperceptible to the human eye, but NASA’s advanced radar technology can detect it.
“Synthetic aperture radar doesn’t directly see water,” explained Yunling Lou, who leads the UAVSAR program at NASA’s Jet Propulsion Laboratory in Southern California. “We’re measuring changes in surface elevation — smaller than a centimeter — that tell us where the water is.”
These surface bulges create what Knight calls an “InSAR recharge signature.” By tracking how these surface bulges migrate from the mountains into the valley, the team hopes to pinpoint where groundwater replenishment occurs and, ultimately, quantify the amount of water naturally recharging the system.
Previous research using satellite-based InSAR (Interferometric Synthetic Aperture Radar) has shown that land in the San Joaquin Valley uplifts and subsides with the seasons, as the groundwater is replenished by Sierra snowmelt. But the satellite radar couldn’t uniquely identify the recharge paths. Knight’s team combined the satellite data with images of underground sediments, acquired using an airborne electromagnetic system, and was able to map the major hidden subsurface water pathways responsible for aquifer recharge.
NASA’s airborne UAVSAR system will provide even more detailed data, potentially allowing researchers to have a clearer view of where and how fast water is soaking back into the ground and recharging the depleted aquifers.
In 2025, NASA’s UAVSAR system on a Gulfstream-III jet (shown over a desert landscape) is conducting six planned advanced radar surveys to map how and where groundwater is recharging parts of California’s southern San Joaquin Valley. Credits: NASA Supporting Farmers and Communities
California’s Central Valley produces over a third of America’s vegetables and two-thirds of its fruits and nuts. The southern portion of this agricultural powerhouse is the San Joaquin Valley, where most farming operations rely heavily on groundwater, especially during drought years.
Water managers have occasionally been forced to impose restrictions on groundwater pumping as aquifer levels drop. Some farmers now drill increasingly deeper wells, driving up costs and depleting reserves.
“Knowing where recharge is happening is vital for smart water management,” said Aaron Fukuda, general manager of the Tulare Irrigation District, a water management agency in Tulare County that oversees irrigation and groundwater recharge projects.
“In dry years, when we get limited opportunities, we can direct flood releases to areas that recharge efficiently, avoiding places where water would just evaporate or take too long to soak in,” Fukuda said. “In wetter years, like 2023, it’s even more crucial — we need to move water into the ground as quickly as possible to prevent flooding and maximize the amount absorbed.”
NASA’s Expanding Role in Water Monitoring
NASA’s ongoing work to monitor and manage Earth’s water combines a range of cutting-edge technologies that complement one another, each contributing unique insights into the challenges of groundwater management.
The upcoming NISAR (NASA-ISRO Synthetic Aperture Radar) mission, a joint project between NASA and the Indian Space Research Organisation (ISRO) set to launch in coming months, will provide global-scale radar data to track land and ice surface changes — including signatures of groundwater movement — every 12 days.
The NISAR satellite (shown in this artist’s concept) has a large radar antenna designed to monitor Earth’s land and ice changes with unprecedented detail. Credits: NASA/JPL-Caltech In parallel, the GRACE satellites — operated by the German Aerospace Center, German Research Centre for Geosciences, and NASA — have transformed global groundwater monitoring by detecting tiny variations in Earth’s gravity, offering a broad view of monthly water storage changes across large regions.
The Gravity Recovery and Climate Experiment and Follow-On (GRACE and GRACE-FO) missions have helped expose major declines in aquifers, including in California’s Central Valley. But their coarser resolution calls for complementary tools that can, for example, pinpoint recharge hotspots with greater precision.
Together, these technologies form a powerful suite of tools that bridge the gap between regional-scale monitoring and localized water management. NASA’s Western Water Applications Office (WWAO) also plays a key role in ensuring that this wealth of data is accessible to water managers and others, offering platforms like the Visualization of In-situ and Remotely-Sensed Groundwater Observation (VIRGO) dashboard to facilitate informed decision-making.
“Airborne campaigns like this one in the San Joaquin test how our technology can deliver tangible benefits to American communities,” said Stephanie Granger, WWAO’s director at NASA’s Jet Propulsion Laboratory. “We partner with local water managers to evaluate tools that have the potential to strengthen water supplies across the Western United States.”
By Emily DeMarco
NASA Headquarters
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Emily DeMarco
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Last Updated Mar 20, 2025 Related Terms
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By NASA
Although NASA’s Lucy spacecraft’s upcoming encounter with the asteroid Donaldjohanson is primarily a mission rehearsal for later asteroid encounters, a new paper suggests that this small, main belt asteroid may have some surprises of its own. New modeling indicates that Donaldjohanson may have been formed about 150 million years ago when a larger parent asteroid broke apart; its orbit and spin properties have undergone significant evolution since.
This artist’s concept compares the approximate size of Lucy’s next asteroid target, Donaldjohanson, to the smallest main belt asteroids previously visited by spacecraft — Dinkinesh, visited by Lucy in November 2023, and Steins — as well as two recently explored near-Earth asteroids, Bennu and Ryugu. Credits: SwRI/ESA/OSIRIS/NASA/Goddard/Johns Hopkins APL/NOIRLab/University of Arizona/JAXA/University of Tokyo & Collaborators When the Lucy spacecraft flies by this approximately three-mile-wide space rock on April 20, 2025, the data collected could provide independent insights on such processes based on its shape, surface geology and cratering history.
“Based on ground-based observations, Donaldjohanson appears to be a peculiar object,” said Simone Marchi, deputy principal investigator for Lucy of Southwest Research Institute in Boulder, Colorado and lead author of the research published in The Planetary Science Journal. “Understanding the formation of Donaldjohanson could help explain its peculiarities.”
“Data indicates that it could be quite elongated and a slow rotator, possibly due to thermal torques that have slowed its spin over time,” added David Vokrouhlický, a professor at the Charles University, Prague, and co-author of the research.
Lucy’s target is a common type of asteroid, composed of silicate rocks and perhaps containing clays and organic matter. The new paper indicates that Donaldjohanson is a likely member of the Erigone collisional asteroid family, a group of asteroids on similar orbits that was created when a larger parent asteroid broke apart. The family originated in the inner main belt not very far from the source regions of the near-Earth asteroids Bennu and Ryugu, recently visited respectively by NASA’s OSIRIS-REx and JAXA’s (Japan Aerospace Exploration Agency’s) Hayabusa2 missions.
“We can hardly wait for the flyby because, as of now, Donaldjohanson’s characteristics appear very distinct from Bennu and Ryugu. Yet, we may uncover unexpected connections,” added Marchi.
“It’s exciting to put together what we’ve been able to glean about this asteroid,” said Keith Noll, Lucy project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But Earth-based observing and theoretical models can only take us so far – to validate these models and get to the next level of detail we need close-up data. Lucy’s upcoming flyby will give us that.”
Donaldjohanson is named for the paleontologist who discovered Lucy, the fossilized skeleton of an early hominin found in Ethiopia in 1974, which is how the Lucy mission got its name. Just as the Lucy fossil provided unique insights into the origin of humanity, the Lucy mission promises to revolutionize our knowledge of the origin of humanity’s home world. Donaldjohanson is the only named asteroid so far to be visited while its namesake is still living.
“Lucy is an ambitious NASA mission, with plans to visit 11 asteroids in its 12-year mission to tour the Trojan asteroids that are located in two swarms leading and trailing Jupiter,” said SwRI’s Dr. Hal Levison, mission principal investigator at the Boulder, Colorado branch of Southwest Research Institute in San Antonio, Texas. “Encounters with main belt asteroids not only provide a close-up view of those bodies but also allow us to perform engineering tests of the spacecraft’s innovative navigation system before the main event to study the Trojans. These relics are effectively fossils of the planet formation process, holding vital clues to deciphering the history of our solar system.”
Lucy’s principal investigator is based out of the Boulder, Colorado, branch of Southwest Research Institute, headquartered in San Antonio. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides overall mission management, systems engineering, and safety and mission assurance. Lockheed Martin Space in Littleton, Colorado, built the spacecraft. Lucy is the 13th mission in NASA’s Discovery Program. NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Discovery Program for the agency’s Science Mission Directorate in Washington.
By Deb Schmid and Katherine Kretke, Southwest Research Institute
Media Contact:
Karen Fox / Molly Wasser
Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
Nancy N. Jones
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Last Updated Mar 17, 2025 EditorMadison OlsonContactNancy N. Jonesnancy.n.jones@nasa.govLocationGoddard Space Flight Center Related Terms
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By European Space Agency
Marking another step towards new insights into Earth’s forests and their role in the carbon cycle, ESA’s groundbreaking Biomass satellite has arrived at Europe's Spaceport in French Guiana, to be prepared for liftoff on a Vega-C rocket at the end of April.
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