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By NASA
Honolulu is pictured here beside a calm sea in 2017. A JPL technology recently detected and confirmed a tsunami up to 45 minutes prior to detection by tide gauges in Hawaii, and it estimated the speed of the wave to be over 580 miles per hour (260 meters per second) near the coast.NASA/JPL-Caltech A massive earthquake and subsequent tsunami off Russia in late July tested an experimental detection system that had deployed a critical component just the day before.
A recent tsunami triggered by a magnitude 8.8 earthquake off Russia’s Kamchatka Peninsula sent pressure waves to the upper layer of the atmosphere, NASA scientists have reported. While the tsunami did not wreak widespread damage, it was an early test for a detection system being developed at the agency’s Jet Propulsion Laboratory in Southern California.
Called GUARDIAN (GNSS Upper Atmospheric Real-time Disaster Information and Alert Network), the experimental technology “functioned to its full extent,” said Camille Martire, one of its developers at JPL. The system flagged distortions in the atmosphere and issued notifications to subscribed subject matter experts in as little as 20 minutes after the quake. It confirmed signs of the approaching tsunami about 30 to 40 minutes before waves made landfall in Hawaii and sites across the Pacific on July 29 (local time).
“Those extra minutes of knowing something is coming could make a real difference when it comes to warning communities in the path,” said JPL scientist Siddharth Krishnamoorthy.
Near-real-time outputs from GUARDIAN must be interpreted by experts trained to identify the signs of tsunamis. But already it’s one of the fastest monitoring tools of its kind: Within about 10 minutes of receiving data, it can produce a snapshot of a tsunami’s rumble reaching the upper atmosphere.
The dots in this graph indicate wave disturbances in the ionosphere as measured be-tween ground stations and navigation satellites. The initial spike shows the acoustic wave coming from the epicenter of the July 29 quake that caused the tsunami; the red squiggle shows the gravity wave the tsunami generated.NASA/JPL-Caltech The goal of GUARDIAN is to augment existing early warning systems. A key question after a major undersea earthquake is whether a tsunami was generated. Today, forecasters use seismic data as a proxy to predict if and where a tsunami could occur, and they rely on sea-based instruments to confirm that a tsunami is passing by. Deep-ocean pressure sensors remain the gold standard when it comes to sizing up waves, but they are expensive and sparse in locations.
“NASA’s GUARDIAN can help fill the gaps,” said Christopher Moore, director of the National Oceanic and Atmospheric Administration Center for Tsunami Research. “It provides one more piece of information, one more valuable data point, that can help us determine, yes, we need to make the call to evacuate.”
Moore noted that GUARDIAN adds a unique perspective: It’s able to sense sea surface motion from high above Earth, globally and in near-real-time.
Bill Fry, chair of the United Nations technical working group responsible for tsunami early warning in the Pacific, said GUARDIAN is part of a technological “paradigm shift.” By directly observing ocean dynamics from space, “GUARDIAN is absolutely something that we in the early warning community are looking for to help underpin next generation forecasting.”
How GUARDIAN works
GUARDIAN takes advantage of tsunami physics. During a tsunami, many square miles of the ocean surface can rise and fall nearly in unison. This displaces a significant amount of air above it, sending low-frequency sound and gravity waves speeding upwards toward space. The waves interact with the charged particles of the upper atmosphere — the ionosphere — where they slightly distort the radio signals coming down to scientific ground stations of GPS and other positioning and timing satellites. These satellites are known collectively as the Global Navigation Satellite System (GNSS).
While GNSS processing methods on Earth correct for such distortions, GUARDIAN uses them as clues.
SWOT Satellite Measures Pacific Tsunami The software scours a trove of data transmitted to more than 350 continuously operating GNSS ground stations around the world. It can potentially identify evidence of a tsunami up to about 745 miles (1,200 kilometers) from a given station. In ideal situations, vulnerable coastal communities near a GNSS station could know when a tsunami was heading their way and authorities would have as much as 1 hour and 20 minutes to evacuate the low-lying areas, thereby saving countless lives and property.
Key to this effort is the network of GNSS stations around the world supported by NASA’s Space Geodesy Project and Global GNSS Network, as well as JPL’s Global Differential GPS network that transmits the data in real time.
The Kamchatka event offered a timely case study for GUARDIAN. A day before the quake off Russia’s northeast coast, the team had deployed two new elements that were years in the making: an artificial intelligence to mine signals of interest and an accompanying prototype messaging system.
Both were put to the test when one of the strongest earthquakes ever recorded spawned a tsunami traveling hundreds of miles per hour across the Pacific Ocean. Having been trained to spot the kinds of atmospheric distortions caused by a tsunami, GUARDIAN flagged the signals for human review and notified subscribed subject matter experts.
Notably, tsunamis are most often caused by large undersea earthquakes, but not always. Volcanic eruptions, underwater landslides, and certain weather conditions in some geographic locations can all produce dangerous waves. An advantage of GUARDIAN is that it doesn’t require information on what caused a tsunami; rather, it can detect that one was generated and then can alert the authorities to help minimize the loss of life and property.
While there’s no silver bullet to stop a tsunami from making landfall, “GUARDIAN has real potential to help by providing open access to this data,” said Adrienne Moseley, co-director of the Joint Australian Tsunami Warning Centre. “Tsunamis don’t respect national boundaries. We need to be able to share data around the whole region to be able to make assessments about the threat for all exposed coastlines.”
To learn more about GUARDIAN, visit:
https://guardian.jpl.nasa.gov
News Media Contacts
Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, Calif.
626-379-6874 / 818-354-0307
jane.j.lee@jpl.nasa.gov / andrew.wang@jpl.nasa.gov
Written by Sally Younger
2025-117
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Preparations for Next Moonwalk Simulations Underway (and Underwater)
A ship plows through rough seas in the Bering Sea in the aftermath of Typhoon Tip, one of the largest hurricanes on record. The Sentinel-6B satellite will provide data crucial to forecasting sea states, information that can help ships avoid danger. CC BY 2.0 NOAA/Commander Richard Behn Sea surface height data from the Sentinel-6B satellite, led by NASA and ESA, will help with the development of marine weather forecasts, alerting ships to possible dangers.
Because most global trade travels by ship, accurate, timely ocean forecasts are essential. These forecasts provide crucial information about storms, high winds, and rough water, and they depend on measurements provided by instruments in the ocean and by satellites including Sentinel-6B, a joint mission led by NASA and ESA (European Space Agency) that will provide essential sea level and other ocean data after it launches this November.
The satellite will eventually take over from its twin, Sentinel-6 Michael Freilich, which launched in 2020. Both satellites have an altimeter instrument that measures sea levels, wind speeds, and wave heights, among other characteristics, which meteorologists feed into models that produce marine weather forecasts. Those forecasts provide information on the state of the ocean as well as the changing locations of large currents like the Gulf Stream. Dangerous conditions can result when waves interact with such currents, putting ships at risk.
“Building on NASA’s long legacy of satellite altimetry data and its real-world impact on shipping operations, Sentinel-6B will soon take on the vital task of improving ocean and weather forecasts to help keep ships, their crews, and cargo safe”, said Nadya Vinogradova Shiffer, lead program scientist at NASA Headquarters in Washington.
Sentinel-6 Michael Freilich and Sentinel-6B are part of the Sentinel-6/Jason-CS (Continuity of Service) mission, the latest in a series of ocean-observing radar altimetry missions that have monitored Earth’s changing seas since the early 1990s. Sentinel-6/Jason-CS is a collaboration between NASA, ESA, the European Union, EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites), and NOAA (U.S. National Oceanic and Atmospheric Administration). The European Commission provided funding support, and the French space agency CNES (Centre National d’Études Spatiales) contributed technical support.
Keeping current
“The ocean is getting busier, but it’s also getting more dangerous,” said Avichal Mehra, deputy director of the Ocean Prediction Center at the National Weather Service in College Park, Maryland. He and his colleagues produce marine weather forecasts using data from ocean-based instruments as well as complementary measurements from five satellites, including Sentinel-6 Michael Freilich. Among those measurements: sea level, wave height, and wind speed. The forecasters derive the location of large currents from changes in sea level.
One of the planet’s major currents, the Gulf Stream is located off the southeastern coast of the United States, but its exact position varies. “Ships will actually change course depending on where the Gulf Stream is and the direction of the waves,” said Mehra. “There have been instances where, in calm conditions, waves interacting with the Gulf Stream have caused damage or the loss of cargo containers on ships.”
Large, warm currents like the Gulf Stream can have relatively sharp boundaries since they are generally higher than their surroundings. Water expands as it warms, so warm seawater is taller than cooler water. If waves interact with these currents in a certain way, seas can become extremely rough, presenting a hazard to even the largest ships.
“Satellite altimeters are the only reliable measurement we have of where these big currents can be,” said Deirdre Byrne, sea surface height team lead at NOAA in College Park.
There are hundreds of floating sensors scattered about the ocean that could pick up parts of where such currents are located, but these instruments are widely dispersed and limited in the area they measure at any one time. Satellites like Sentinel-6B offer greater spatial coverage, measuring areas that aren’t regularly monitored and providing essential information for the forecasts that ships need.
Consistency is key
Sentinel-6B won’t just help marine weather forecasts through its near-real-time data, though. It will also extend a long-term dataset featuring more than 30 years of sea level measurements, just as Sentinel-6 Michael Freilich does today.
“Since 1992, we have launched a series of satellites that have provided consistent sea level observations from the same orbit in space. This continuity allows each new mission to be calibrated against its predecessors, providing measurements with centimeter-level accuracy that don’t drift over time,” said Severine Fournier, Sentinel-6B deputy project scientist at NASA’s Jet Propulsion Laboratory in Southern California.
This long-running, repeated measurement has turned this dataset into the gold standard sea level measurement from space — a reference against which data from other sea level satellites is checked. It also serves as a baseline, giving forecasters a way to tell what ocean conditions have looked like over time and how they are changing now. “This kind of data can’t be easily replaced,” said Mehra.
More about Sentinel-6B
Sentinel-6/Jason-CS was jointly developed by ESA, EUMETSAT, NASA, and NOAA, with funding support from the European Commission and technical support from CNES.
A division of Caltech in Pasadena, JPL contributed three science instruments for each Sentinel-6 satellite: the Advanced Microwave Radiometer, the Global Navigation Satellite System – Radio Occultation, and the Laser Retroreflector Array. NASA is also contributing launch services, ground systems supporting operation of the NASA science instruments, the science data processors for two of these instruments, and support for the U.S. members of the international Ocean Surface Topography and Sentinel-6 science teams.
For more about Sentinel-6/Jason-CS, visit:
https://sealevel.jpl.nasa.gov/missions/jason-cs-sentinel-6
News Media Contacts
Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, Calif.
626-491-1943 / 626-379-6874
jane.j.lee@jpl.nasa.gov / andrew.wang@jpl.nasa.gov
2025-116
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Last Updated Sep 11, 2025 Related Terms
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Space changes you. It strengthens some muscles, weakens others, shifts fluids within your body, and realigns your sense of balance. NASA’s Human Research Program works to understand—and sometimes even counter—those changes so astronauts can thrive on future deep space missions.
NASA astronaut Loral O’Hara pedals on the Cycle Ergometer Vibration Isolation System (CEVIS) inside the International Space Station’s Destiny laboratory module.NASA Astronauts aboard the International Space Station work out roughly two hours a day to protect bone density, muscle strength and the cardiovascular system, but the longer they are in microgravity, the harder it can be for the brain and body to readapt to gravity’s pull. After months in orbit, returning astronauts often describe Earth as heavy, loud, and strangely still. Some reacclimate within days, while other astronauts take longer to fully recover.
Adjusting to Gravity
NASA’s SpaceX Crew-7 astronaut Jasmin Moghbeli after landing in the Gulf of America on March 12, 2024, completing 197 days in space.NASA/Joel Kowsky The crew of NASA’s SpaceX Crew-7 mission— NASA astronaut Jasmin Moghbeli, ESA (European Space Agency) astronaut Andreas Mogensen, JAXA (Japan Aerospace Exploration Agency) astronaut Satoshi Furukawa, and Roscosmos cosmonaut Konstantin Borisov—landed in March 2024 after nearly 200 days in space. One of the first tests volunteer crew members completed was walking with their eyes open and then closed.
“With eyes closed, it was almost impossible to walk in a straight line,” Mogensen said. In space, vision is the primary way astronauts orient themselves, but back on Earth, the brain must relearn how to use inner-ear balance signals. Moghbeli joked her first attempt at the exercise looked like “a nice tap dance.”
“I felt very wobbly for the first two days,” Moghbeli said. “My neck was very tired from holding up my head.” She added that, overall, her body readapted to gravity quickly.
Astronauts each recover on their own timetable and may encounter different challenges. Mogensen said his coordination took time to return. Furukawa noted that he could not look down without feeling nauseated. “Day by day, I recovered and got more stable,” he said.
NASA astronaut Loral O’Hara after landing in a remote area near the town of Zhezkazgan, Kazakhstan, on April 6, 2024.NASA/Bill Ingalls NASA astronaut Loral O’Hara returned in April 2024 after 204 days in space. She said she felt almost completely back to normal a week after returning to Earth. O’Hara added that her prior experience as an ocean engineer gave her insight into space missions. “Having those small teams in the field working with a team somewhere else back on shore with more resources is a good analog for the space station and all the missions we’re hoping to do in the future,” she said.
NASA astronaut Nichole Ayers, who flew her first space mission with NASA’s SpaceX Crew-10, noted that the brain quickly adapts to weightlessness by tuning out the vestibular system, which controls balance. “Then, within days of being back on Earth, it remembers again—it’s amazing how fast the body readjusts,” she said.
Expedition 69 NASA astronaut Frank Rubio outside the Soyuz MS-23 spacecraft after landing near the town of Zhezkazgan, Kazakhstan, on Sept. 27, 2023. NASA/Bill Ingalls When NASA astronaut Frank Rubio landed in Kazakhstan in September 2023, he had just completed a record 371-day mission—the longest single U.S. spaceflight.
Rubio said his body adjusted to gravity right away, though his feet and lower back were sore after more than a year without weight on them. Thanks to consistent workouts, Rubio said he felt mostly recovered within a couple of weeks.
Mentally, extending his mission from six months to a year was a challenge. “It was a mixed emotional roller coaster,” he said, but regular video calls with family kept him grounded. “It was almost overwhelming how much love and support we received.”
Crew-8 astronauts Matt Dominick, Jeanette Epps, Michael Barratt, and cosmonaut Alexander Grebenkin splashed down in October 2024 after 235 days on station. Dominick found sitting on hard surfaces uncomfortable at first. Epps felt the heaviness of Earth immediately. “You have to move and exercise every day, regardless of how exhausted you feel,” she said.
Barratt, veteran astronaut and board certified in internal and aerospace medicine, explained that recovery differs for each crew member, and that every return teaches NASA something new.
Still a Challenge, Even for Space Veterans
NASA astronaut Suni Williams is helped out of a SpaceX Dragon spacecraft aboard the SpaceX recovery ship after splashing down off the coast of Tallahassee, Florida, March 18, 2025. NASA/Keegan Barber Veteran NASA astronauts Suni Williams and Butch Wilmore returned from a nine-month mission with Crew-9 in early 2025. Despite her extensive spaceflight experience, Williams said re-adapting to gravity can still be tough. “The weight and heaviness of things is surprising,” she said. Like others, she pushed herself to move daily to regain strength and balance.
NASA astronaut Don Pettit arrives at Ellington Field in Houston on April 20, 2025, after returning to Earth aboard the Soyuz MS-25 spacecraft. NASA/Robert Markowitz NASA astronaut Don Pettit, also a veteran flyer, came home in April 2025 after 220 days on the space station. At 70 years old, he is NASA’s oldest active astronaut—but experience did not make gravity gentler. During landing, he says he was kept busy, “emptying the contents of my stomach onto the steppes of Kazakhstan.” Microgravity had eased the aches in his joints and muscles, but Earth’s pull brought them back all at once.
Pettit said his recovery felt similar to earlier missions. “I still feel like a little kid inside,” he said. The hardest part, he explained, isn’t regaining strength in big muscle groups, but retraining the small, often-overlooked muscles unused in space. “It’s a learning process to get used to gravity again.”
Recovery happens day by day—with help from exercise, support systems, and a little humor. No matter how long an astronaut is in space, every journey back to Earth is unique.
The Human Research Program help scientists understand how spaceflight environments affect astronaut health and performance and informs strategies to keep crews healthy for future missions to the Moon, Mars, and beyond. The program studies astronauts before, during, and after spaceflight to learn how the human body adapts to living and working in space. It also collects data through Earth-based analog missions that can help keep astronauts safer for future space exploration.
To learn more about how microgravity affects the human body and develop new ways to help astronauts stay healthy, for example, its scientists conduct bedrest studies – asking dozens of volunteers to spend 60 days in bed with their heads tilted down at a specific angle. Lying in this position tricks the body into responding as it would if the body was in space which allows scientists to trial interventions to hopefully counter some of microgravity’s effects. Such studies, through led by NASA, occur at the German Aerospace Center’s Cologne campus at a facility called :envihab – a combination of “environment” and “habitat.”
Additional Earth-based insights come from the Crew Health and Performance Exploration Analog (CHAPEA) and the Human Exploration Research Analog (HERA) at NASA’s Johnson Space Center in Houston. Both analogs recreate the remote conditions and scenarios of deep space exploration here on Earth with volunteer crews who agree to live and work in the isolation of ground-based habitats and endure challenges like delayed communication that simulates the type of interactions that will occur during deep space journeys to and from Mars. Findings from these ground-based missions and others will help NASA refine its future interventions, strategies, and protocols for astronauts in space.
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