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Copernicus Sentinel-1: radar vision for Copernicus
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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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Last Updated Mar 20, 2025 Related Terms
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On Feb. 11, 2000, space shuttle Endeavour took to the skies on its 14th trip into space on the Shuttle Radar Topography Mission (SRTM). The international STS-99 crew included Commander Kevin Kregel, Pilot Dominic Gorie, and Mission Specialists Gerhard Thiele of Germany representing the European Space Agency, Janet Kavandi, Janice Voss, who served as payload commander on the mission, and Mamoru Mohri of the National Space Development Agency (NASDA) of Japan, now the Japan Aerospace Exploration Agency.
During their 11-day mission, the astronauts used the radar instruments in Endeavour’s payload bay to obtain elevation data on a near global scale. The data produced the most complete, high-resolution digital elevation model of the Earth. The SRTM comprised a cooperative effort among NASA with the Jet Propulsion Laboratory (JPL) in Pasadena, California, managing the project, the Department of Defense’s National Imagery and Mapping Agency, the German space agency, and the Italian space agency. Prior to SRTM, scientists had a more detailed topographic map of Venus than of the Earth, thanks to the Magellan radar mapping mission.
The STS-99 crew patch. Official photo of the STS-99 crew of Janice Voss, left, Mamoru Mohri of the National Space Development Agency of Japan, now the Japan Aerospace Exploration Agency, Kevin Kregel, Dominic Gorie, Gerhard Thiele of Germany representing the European Space Agency, and Janet Kavandi. The Shuttle Radar Topography Mission patch. Schematic of the Space Radar Topography Mission payloads including the deployed mast. The mast antenna during preflight processing. NASA assigned the STS-99 crew in October 1998. For Kregel, selected by NASA as an astronaut in 1992, STS-99 marked his fourth trip to space, having served as pilot on STS-70 and STS-78 and commanded STS-87. Gorie and Kavandi, both selected in 1994, previously flew together as pilot and mission specialist, respectively, on STS-91, the final Shuttle Mir docking mission. Voss, selected in 1990, served as a mission specialist on STS-57 and STS-63, and as payload commander on STS-83 and STS-94. NASDA selected Mohri as an astronaut in 1985 and he previously flew as a payload specialist on STS-47, the Spacelab-J mission. Selected as an astronaut by the German space agency in 1987, Thiele joined the European Astronaut Corps in 1998, completing his first spaceflight on STS-99.
The SRTM used an innovative technique called radar interferometry to image the Earth’s landmasses at resolutions up to 30 times greater than previously achieved. Two of the synthetic aperture radar instruments comprising the SRTM payload had flown previously, on the STS-59 Shuttle Radar Laboratory-1 (SRL-1) and the STS-68 SRL-2 missions in April and October 1994, respectively. A second receiver antenna, placed at the end of a 200-foot deployable mast, enabled the interferometry during SRTM.
The SRTM payload in Endeavour’s cargo bay in the orbiter processing facility. Endeavour rolls out to Launch Pad 39A. The STS-99 crew walks out of crew quarters for the van ride to the launch pad. Workers rolled Endeavour to the Vehicle Assembly Building on Dec. 2 for mating with its external tank and solid rocket boosters, and then out to Launch Pad 39A on Dec. 13. The astronauts traveled to Kennedy to participate in the Terminal Countdown Demonstration Test Jan. 11-14, returning afterwards to Houston for final training. They traveled back to Kennedy on Jan. 27 for the first launch attempt four days later. After two launch attempts, the STS-99 mission prepared to liftoff on Feb. 11, 2000.
Liftoff! Space shuttle Endeavour takes to the skies to begin the STS-99 mission. At 12:43 p.m. EST, Endeavour thundered into the sky from Kennedy’s Launch Pad 39A to begin the STS-99 mission. Thirty-seven minutes later, a brief firing of the orbiter’s two engines placed Endeavour in the proper 145-mile orbit for the radar scanning.
The SRTM instruments in Endeavour’s payload bay with the mast holding the second antenna receiver deployed at right. The antenna at the end of the deployed mast. STS-99 astronauts Janet Kavandi, left, Dominic Gorie, and Mamoru Mohri in Endeavour’s middeck. Astronaut Janice Voss in the commander’s seat on Endeavour’s flight deck. Astronauts Kevin Kregel, left, and Gerhard Thiele on Endeavour’s flight deck. Shortly after reaching orbit, the crew opened the payload bay doors and deployed the shuttle’s radiators. Kavandi and Thiele turned on the instruments, deployed the 200-foot mast, and conducted initial checkouts of the radars. The crew split into two shifts to enable data collection around the clock during the mission. After overseeing the initial activation of the radars, the red shift of Kregel, Kavandi, and Thiele began their first sleep period as the blue shift of Gorie, Voss, and Mohri picked up with activation and began the first data takes.
The major crew activity for SRTM involved changing tapes every 30 minutes. The SRTM generated 332 high density tapes during more than 222 hours of data collection and these recordings covered 99.96 percent of the planned observations. Data collection finished on the mission’s 10th flight day, after which the astronauts reeled the mast back into its container in the payload bay.
EarthKAM image of the greater Boston area. The EarthKAM camera mounted in a space shuttle window. STS-99 crew Earth observation photograph of El Paso, Texas, and Ciudad Juarez, Mexico. STS-99 crew Earth observation photograph of the Galapagos Islands. STS-99 crew Earth observation photograph of the greater New York area. STS-99 crew Earth observation photograph of Erg Chech, or sand sea, in the Algerian Sahara. NASA’s EarthKAM program enabled middle school students to remotely take photographs of the Earth using an electronic still camera mounted in one of the shuttle’s windows. The University of California at San Diego houses the control center for EarthKAM, linked with middle schools via the Internet. Students choose Earth targets of interest, and the camera takes photos of that region as the shuttle passes overhead. A then-record 75 schools from around the world participated in the EarthKAM project on STS-99, the camera returning 2,715 images of the Earth.
The STS-99 astronauts also spent time taking photographs of the Earth using handheld cameras and the high inclination orbit enabled views of some parts of the Earth rarely seen by shuttle astronauts.
The six-person STS-99 crew pose for their inflight photo. Kevin Kregel guides Endeavour to a smooth touchdown on the Shuttle Landing Facility at NASA’s Kennedy Space Center in Florida. The STS-99 crew poses with NASA Administrator Daniel Goldin under Endeavour at the Shuttle Landing Facility at NASA’s Kennedy Space Center in Florida. Kevin Kregel addresses the crowd at Houston’s Ellington Field during the welcome home ceremony for the STS-99 crew. On Feb. 22, the crew closed Endeavour’s payload bay doors, donned their launch and entry suits, and strapped themselves into their seats for entry and landing. Kregel piloted Endeavour to a smooth landing on Kennedy’s Shuttle Landing Facility. The crew had flown 181 orbits around the Earth in 11 days, 5 hours, and 39 minutes. Enjoy the crew narrate a video about the STS-99 mission.
Postscript
Final coverage map for the SIR-C radar, indicating 99.96 percent coverage of planned land mass targets, with many areas imaged more than once.
False-color image generated from SRTM data of the island of Oahu. False-color image generated from SRTM data of Mt. Cotopaxi in Ecuador, the tallest active volcano in the world. During the 11-day mission, SRTM collected more than one trillion data points, generating 12.3 terabytes of 3-D data of the Earth. Earnest Paylor, SRTM program scientist at NASA Headquarters in Washington, D.C., called the mission “a magnificent accomplishment.” He cited that SRTM imaged by radar equatorial regions of the Earth previously unmapped due to constant cloud cover.
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NASA’s UAVSAR airborne radar instrument captured data in fall 2024 showing the mo-tion of landslides on the Palos Verdes Peninsula following record-breaking rainfall in Southern California in 2023 and another heavy-precipitation winter in 2024. Darker red indicates faster motion.NASA Earth Observatory Analysis of data from NASA radar aboard an airplane shows that the decades-old active landslide area on the Palos Verdes Peninsula has expanded.
Researchers at NASA’s Jet Propulsion Laboratory in Southern California used data from an airborne radar to measure the movement of the slow-moving landslides on the Palos Verdes Peninsula in Los Angeles County. The analysis determined that, during a four-week period in the fall of 2024, land in the residential area slid toward the ocean by as much as 4 inches (10 centimeters) per week.
Portions of the peninsula, which juts into the Pacific Ocean just south of the city of Los Angeles, are part of an ancient complex of landslides and has been moving for at least the past six decades, affecting hundreds of buildings in local communities. The motion accelerated, and the active area expanded following record-breaking rainfall in Southern California in 2023 and heavy precipitation in early 2024.
To create this visualization, the Advanced Rapid Imaging and Analysis (ARIA) team used data from four flights of NASA’s Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) that took place between Sept. 18 and Oct. 17. The UAVSAR instrument was mounted to a Gulfstream III jet flown out of NASA’s Armstrong Flight Research Center in Edwards, California, and the four flights were planned to estimate the speed and direction of the landslides in three dimensions.
In the image above, colors indicate how fast parts of the landslide complex were moving in late September and October, with the darkest reds indicating the highest speeds. The arrows represent the direction of horizontal motion. The white solid lines are the boundaries of the active landslide area as defined in 2007 by the California Geological Survey.
“In effect, we’re seeing that the footprint of land experiencing significant impacts has expanded, and the speed is more than enough to put human life and infrastructure at risk,” said Alexander Handwerger, the JPL landslide scientist who performed the analysis.
The insights from the UAVSAR flights were part of a package of analyses by the ARIA team that also used data from ESA’s (the European Space Agency’s) Copernicus Sentinel-1A/B satellites. The analyses were provided to California officials to support the state’s response to the landslides and made available to the public at NASA’s Disaster Mapping Portal.
Handwerger is also the principal investigator for NASA’s upcoming Landslide Climate Change Experiment, which will use airborne radar to study how extreme wet or dry precipitation patterns influence landslides. The investigation will include flights over coastal slopes spanning the California coastline.
More About ARIA, UAVSAR
The ARIA mission is a collaboration between JPL and Caltech, which manages JPL for NASA, to leverage radar and optical remote-sensing, GPS, and seismic observations for science as well as to aid in disaster response. The project investigates the processes and impacts of earthquakes, volcanoes, landslides, fires, subsurface fluid movement, and other natural hazards.
UAVSAR has flown thousands of radar missions around the world since 2007, studying phenomena such as glaciers and ice sheets, vegetation in ecosystems, and natural hazards like earthquakes, volcanoes, and landslides.
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Andrew Wang / Jane J. Lee
Jet Propulsion Laboratory, Pasadena, Calif.
626-379-6874 / 818-354-0307
andrew.wang@jpl.nasa.gov / jane.j.lee@jpl.nasa.gov
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Last Updated Jan 31, 2025 Related Terms
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