NASA Uses Advanced Radar to Track Groundwater in California

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NASA Uses Advanced Radar to Track Groundwater in California

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.    

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.  

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.    

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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NASA Langley Dedicates Artemis Moon Tree

A tree that sprouted from a seed that journeyed around the Moon and back is growing at NASA’s Langley Research Center in Hampton, Virginia.

NASA’s Acting Associate Administrator for NASA’s Exploration Systems Development Mission Directorate Lori Glaze and NASA Langley Acting Center Director Trina Dyal spoke at a dedication ceremony for the Artemis Moon Tree, a loblolly pine, at the center March 12.

“I wanted to quote an old Greek proverb that more or less says something like, ‘Society grows when its elders plant trees whose shade they know they shall never sit in,’ ” said Glaze. “I love that. We always talk about how we stand on the shoulders of giants. Those giants planted seeds, and we are still benefiting from the tremendous roots of those trees,”

The young tree, only about two feet tall right now, is growing in an area between NASA Langley’s Integrated Engineering Services Building and its Measurement Systems Laboratory. The pine is surrounded by a wire plant protector. A yellow label identifies the species and the location of the U.S. Department of Agriculture Forest Services nursery where the seedling was grown — Charles E. Bessey Nursery in Halsey, Nebraska. A small plaque marks its status as a Moon Tree.

“This, we plant here for all future generations to be inspired and to continue on the amazing legacy of what we’re doing,” said Glaze. “Our return to the lunar surface and our journey to Mars through the Artemis campaign is really going to lay the foundation for that future of exploration that right now we’re only dreaming about. With your help, through Langley and the rest of our NASA colleagues and partners, we’re going to achieve those visions.”

The loblolly seed was one of many that flew on the Artemis I mission Nov. 16 to Dec. 11, 2022 — journeying 270,000 miles from Earth aboard the Orion spacecraft. NASA’s Office of STEM Engagement partnered with the Forest Services to fly the seeds aboard Artemis I as part of a national STEM Engagement and conservation education initiative. 

In addition to loblolly pines, tree species on the flight included sycamores, sweetgums, Douglas firs, and giant sequoias. The Forest Services germinated the seeds.

Locally, NASA Langley’s loblolly pine is one of three Artemis Moon Trees. The Virginia Living Museum in Newport News and the Virginia Zoo in Norfolk were also selected as Moon Tree stewards, and also received loblolly pines.

The Artemis Moon Trees take inspiration from their Apollo precursors. In 1971, NASA astronaut Stuart Roosa, the command module pilot for the Apollo 14 mission and a former U.S. Department of Agriculture Forest Services smoke jumper, carried tree seeds into lunar orbit. The Apollo 14 Moon Trees were disseminated to national monuments and dignitaries around the world, with a large number distributed as part of the nation’s bicentennial event.  

One of those Moon Trees, a sycamore, was planted at Albert W. Patrick III Elementary School in the Fox Hill area of Hampton in 1976. Sixth grader Marjorie White wrote a poem called “A Tree Lives” that won a contest to earn the honor.

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Fallout from the Unauthorized Gemini III Space Sandwich

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Fallout from the Unauthorized Gemini III Space Sandwich

“I hid a sandwich in my spacesuit,” Astronaut John W. Young confessed in the April 2, 1965, issue of Life Magazine. The conversation about and the consumption of the sandwich, which lasted only about 30 seconds during the Gemini III flight, became a serious matter that drew the ire of Congress and NASA’s administrator after the crew returned home. Congress was particularly upset and brought the matter to leadership’s attention at hearings about NASA’s 1966 budget. Representative George E. Shipley was especially disgusted, knowing how much money and time NASA had spent to prepare the Gemini III spacecraft for launch. The fact that a crewmember brought something into the crew cabin, which Shipley likened to a “surgeon’s operating room,” put the techniques used to prevent a spaceflight mission from failing at risk; crumbs could have made their way behind instrument panels interfering with the operation of flight equipment and the loss of the mission and its crew. Shipley called Young’s antics “foolish” and asked NASA leaders to share their thoughts.

A Beef with Corned Beef

George Mueller, associate administrator for Manned Space Flight, stated unequivocally that the agency did not “approve [of] unauthorized objects such as sandwiches going on board the spacecraft.” And he promised Shipley that NASA has “taken steps, obviously, to prevent recurrence of corned beef sandwiches in future flights. There was no detriment to the experimental program that was carried on, nor was there any detriment to the actual carrying out of the mission because of the ingestion of the sandwich.” Manned Spacecraft Center Director Robert R. Gilruth was more forgiving of Young’s decision. These sort of antics, he told the committee, helped the crews to “break up the strain” of spaceflight, and he hesitated “to be too strict in the future by laying down a lot of rules for men who have this responsibility and who, in all the flights so far, have done such good jobs.” Webb disagreed and said, “this is the United States of America’s space program and, as a matter of policy, we are not going to permit individuals to superimpose their judgment as to what is going to be taken on these flights. I think it is fine for Dr. Gilruth to take a very strong position with respect to the individuality of these men, but from those of us who have to look at the totality of the matter, this was not an adequate performance by an astronaut.”

The loss of a Gemini mission, especially one so early in the program, would have been particularly challenging for an agency attempting to land humans on the Moon where each mission built on the previous flight. The United States was in a race with the Soviet Union, and for Congress at least, the purpose of Gemini and the cost of the space program was far too serious for these sorts of fun and games. For NASA Administrator James Webb, it was a sign that Gilruth was too lax when it came to managing his astronauts. Gemini III was just one example of the lack of control he noticed, and he pressed Gilruth for a report on the sandwich incident to determine if Young should be disciplined or at the very least reprimanded.

The In-Flight Meal

Young hatched the idea during training, when his commander, Virgil I. “Gus” Grissom grew “bored” with the food they practiced with for the mission. Grissom regularly complained about the dehydrated “delicacies” food scientists concocted. Bringing a sandwich onboard, an item that was freshly made and did not have to be rehydrated, “seemed like a fun idea at the time” to Young.

One of the goals of their flight was to evaluate NASA’s flight food packaging and whether the containers leaked when foods were reconstituted, as well as the procedures for disposing of the meal and its packaging after eating. Foods included rehydratable items such as chicken bites, applesauce, or drinks, and compressed foods such as brownie bites. The Gemini food system was not haute cuisine, however, and crews complained about its taste. Young described the chicken bites as “barely edible” in his post-flight debriefing. Don L. Lind, a scientist-astronaut selected in 1967, described the early Gemini food as “strange.” Their class took some to jungle survival training in Panama, and while no one wanted to eat it on the first two days, by the third day they were so hungry that they were willing to give it a try. Another problem was that all rehydrated meals for Gemini were mixed with cold water, which made them less appetizing than a hot meal.

A freshly made corned beef sandwich made at a local restaurant sounded like a better option, so Young had fellow astronaut and backup command pilot Walter M. “Wally” Schirra pick one up. Schirra purchased the sandwich for Young, and as he headed out to the launchpad, Young put it in the pocket of his pressure suit.

Nearly two hours into the flight, as Young started his food and waste evaluation, he pulled out the sandwich from his suit and offered it to his commander. As captured on the air-to-ground recordings, Grissom asked what it was and where it came from. “I brought it with me,” Young responded, “Let’s see how it tastes.” He didn’t expect the sandwich to be so pungent, “Smells, doesn’t it?” Grissom took a bite but found the rye crumbled so he placed the sandwich in his suit pocket to prevent the crumbs from floating about the cabin.

Where did that come from?

Gus Grissom

Gemini III Commander

Two days later, nearly a thousand members of the media from the United States and around the world gathered to hear from the crew and NASA management at the postflight press conference at the Carriage House Motel in Cocoa Beach, Florida. Space reporter Bill Hines asked Young about the sandwich, erroneously referring to it as a “baloney sandwich,” and what happened when Gus was offered a taste. “And,” he asked, “what became of the sandwich?” Young seemed surprised, “How did you find out about that?” and then laughed adding Grissom “ate the sandwich.”

Carry-on Restrictions for Spaceflights

Ironically the Gemini Program offered astronauts more control over their flights than during Project Mercury, including the ability to maneuver their spacecraft and to be more independent from Mission Control; but the uproar over this event led NASA to draft rules about what astronauts could and could not take onboard a spacecraft. Starting with Gemini IV, flight crews had to present a list of items they planned to take on their missions. Prohibited items naturally included sandwiches as well as bulky or heavy items or metal that could negatively impact the operation of spacecraft equipment. (NASA still allowed astronauts to take personal items such as wedding bands or coins for families and friends in their personal preference kit.)

Young never received a formal reprimand for the incident but was made aware of Congress’s frustration. Others in the corps were advised to avoid similar stunts and to focus on the mission. The decision to bring a sandwich onboard did not have a negative impact on Young’s career. He was the first astronaut to fly to space six times —two Gemini missions; two Apollo missions, including the dress rehearsal for the first lunar landing; and two space shuttle missions including STS-1, known as the bravest test flight in history. He also served as chief of the Astronaut Office for 13 years.

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Next-Generation Water Satellite Maps Seafloor From Space

More accurate maps based on data from the SWOT mission can improve underwater navigation and result in greater knowledge of how heat and life move around the world’s ocean.

There are better maps of the Moon’s surface than of the bottom of Earth’s ocean. Researchers have been working for decades to change that. As part of the ongoing effort, a NASA-supported team recently published one of the most detailed maps yet of the ocean floor, using data from the SWOT (Surface Water and Ocean Topography) satellite, a collaboration between NASA and the French space agency CNES (Centre National d’Études Spatiales).

Ships outfitted with sonar instruments can make direct, incredibly detailed measurements of the ocean floor. But to date, only about 25% of it has been surveyed in this way. To produce a global picture of the seafloor, researchers have relied on satellite data.

Why Seafloor Maps Matter

More accurate maps of the ocean floor are crucial for a range of seafaring activities, including navigation and laying underwater communications cables. “Seafloor mapping is key in both established and emerging economic opportunities, including rare-mineral seabed mining, optimizing shipping routes, hazard detection, and seabed warfare operations,” said Nadya Vinogradova Shiffer, head of physical oceanography programs at NASA Headquarters in Washington.

Accurate seafloor maps are also important for an improved understanding of deep-sea currents and tides, which affect life in the abyss, as well as geologic processes like plate tectonics. Underwater mountains called seamounts and other ocean floor features like their smaller cousins, abyssal hills, influence the movement of heat and nutrients in the deep sea and can attract life. The effects of these physical features can even be felt at the surface by the influence they exert on ecosystems that human communities depend on.

Mapping the seafloor isn’t the SWOT mission’s primary purpose. Launched in December 2022, the satellite measures the height of water on nearly all of Earth’s surface, including the ocean, lakes, reservoirs, and rivers. Researchers can use these differences in height to create a kind of topographic map of the surface of fresh- and seawater. This data can then be used for tasks such as assessing changes in sea ice or tracking how floods progress down a river.

“The SWOT satellite was a huge jump in our ability to map the seafloor,” said David Sandwell, a geophysicist at Scripps Institution of Oceanography in La Jolla, California. He’s used satellite data to chart the bottom of the ocean since the 1990s and was one of the researchers responsible for the SWOT-based seafloor map, which was published in the journal Science in December 2024.

How It Works

The study authors relied the fact that because geologic features like seamounts and abyssal hills have more mass than their surroundings, they exert a slightly stronger gravitational pull that creates small, measurable bumps in the sea surface above them. These subtle gravity signatures help researchers predict the kind of seafloor feature that produced them.

Through repeated observations — SWOT covers about 90% of the globe every 21 days — the satellite is sensitive enough to pick up these minute differences, with centimeter-level accuracy, in sea surface height caused by the features below. Sandwell and his colleagues used a year’s worth of SWOT data to focus on seamounts, abyssal hills, and underwater continental margins, where continental crust meets oceanic crust.

Previous ocean-observing satellites have detected massive versions of these bottom features, such as seamounts over roughly 3,300 feet (1 kilometer) tall. The SWOT satellite can pick up seamounts less than half that height, potentially increasing the number of known seamounts from 44,000 to 100,000. These underwater mountains stick up into the water, influencing deep sea currents. This can concentrate nutrients along their slopes, attracting organisms and creating oases on what would otherwise be barren patches of seafloor.

Looking Into the Abyss

The improved view from SWOT also gives researchers more insight into the geologic history of the planet.

“Abyssal hills are the most abundant landform on Earth, covering about 70% of the ocean floor,” said Yao Yu, an oceanographer at Scripps Institution of Oceanography and lead author on the paper. “These hills are only a few kilometers wide, which makes them hard to observe from space. We were surprised that SWOT could see them so well.”

Abyssal hills form in parallel bands, like the ridges on a washboard, where tectonic plates spread apart. The orientation and extent of the bands can reveal how tectonic plates have moved over time. Abyssal hills also interact with tides and deep ocean currents in ways that researchers don’t fully understand yet.

The researchers have extracted nearly all the information on seafloor features they expected to find in the SWOT measurements. Now they’re focusing on refining their picture of the ocean floor by calculating the depth of the features they see. The work complements an effort by the international scientific community to map the entire seafloor using ship-based sonar by 2030. “We won’t get the full ship-based mapping done by then,” said Sandwell. “But SWOT will help us fill it in, getting us close to achieving the 2030 objective.”

More About SWOT

The SWOT satellite was jointly developed by NASA and CNES, with contributions from the Canadian Space Agency (CSA) and the UK Space Agency. NASA’s Jet Propulsion Laboratory, managed for the agency by Caltech in Pasadena, California, leads the U.S. component of the project. For the flight system payload, NASA provided the Ka-band radar interferometer (KaRIn) instrument, a GPS science receiver, a laser retroreflector, a two-beam microwave radiometer, and NASA instrument operations. The Doppler Orbitography and Radioposition Integrated by Satellite system, the dual frequency Poseidon altimeter (developed by Thales Alenia Space), the KaRIn radio-frequency subsystem (together with Thales Alenia Space and with support from the UK Space Agency), the satellite platform, and ground operations were provided by CNES. The KaRIn high-power transmitter assembly was provided by CSA.

To learn more about SWOT, visit:

https://swot.jpl.nasa.gov

News Media Contacts

Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0307 / 626-379-6874
jane.j.lee@jpl.nasa.gov / andrew.wang@jpl.nasa.gov

2025-040

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