How NASA and CNES’s SWOT Satellite Gave Scientists the Most Detailed View Ever of a Pacific Tsunami

The Earth’s oceans are home to some of the most powerful natural forces on the planet, but until recently, much of their behavior—especially during extreme events—has remained hidden beneath the surface. In 2025, an extraordinary moment occurred when a joint NASA and French space agency (CNES) satellite captured the first high-resolution, spaceborne view of a tsunami as it raced across the Pacific Ocean. This unprecedented observation is already reshaping how scientists understand tsunami physics, improving forecasting models, and offering new hope for coastal communities at risk from future disasters.

On July 29, 2025, a massive magnitude 8.8 earthquake struck off the Kuril-Kamchatka subduction zone near Russia, triggering a Pacific-wide tsunami. This powerful wave traveled thousands of miles across deep ocean waters, generating a rare scientific opportunity for researchers. As the tsunami spread, the Surface Water and Ocean Topography (SWOT) satellite happened to pass overhead, mapping an extraordinary swath of ocean surface with unprecedented detail. This watershed moment provided scientists with data that simply wasn’t possible from traditional instruments.

Launched in December 2022 as a collaboration between NASA and the Centre National d’Études Spatiales (CNES), SWOT was designed to survey Earth’s water — both freshwater and ocean — by measuring surface topography across a broad swath up to about 120 kilometers wide. Its Ka-band Radar Interferometer (KaRIn) instrument uses precision radar to detect very small changes in water surface height, creating detailed maps of sea level variations that had previously been unobservable at this scale.

Until SWOT’s observation, tsunami detection in the open ocean largely depended on deep-ocean buoys like the Deep-ocean Assessment and Reporting of Tsunamis (DART) array, which records wave height at fixed points but cannot capture the full picture of how a tsunami evolves across the sea surface. A DART buoy can tell scientists that a tsunami passed by, but it provides no direct image or continuous swath of its expanse. SWOT changed that.

The satellite’s wide swath of high-resolution data captured the leading edge of the tsunami roughly 70 minutes after the earthquake struck. Unlike earlier views that showed tsunamis as simple, uniform wave fronts, SWOT’s observations revealed a more complex reality: the tsunami exhibited a braided pattern of energy, with multiple wave peaks and dispersive behavior spreading across hundreds of miles of ocean. This finding challenges the long-held assumption that tsunamis travel as non-dispersive waves with a single dominant crest, suggesting instead that their mid-ocean behavior can be far more intricate and variable.

Experts describe this breakthrough as akin to acquiring a new pair of glasses for ocean scientists. With SWOT’s data, they can track not only the tsunami’s height but also its shape, direction, and how its energy dissipates across the open sea—information that has been missing from traditional forecasting and modeling approaches. These insights are crucial because what happens in the deep ocean has a direct impact on how a tsunami behaves as it approaches shallow coastal waters.

This satellite observation arrives at a time when improving tsunami forecasting is a global priority. Historical events such as the 2004 Indian Ocean tsunami highlighted the devastating human toll that poorly predicted or undetected tsunamis can inflict. By enhancing our understanding of how tsunamis propagate, researchers hope to refine early-warning systems and provide more accurate predictions of wave arrival times, heights, and potential impact zones along vulnerable coastlines.

What the Satellite Discovery Reveals

The detailed satellite data revealed several surprising features about the tsunami generated by the 2025 Kuril-Kamchatka earthquake:

• Complex wave patterns: Instead of a single, smooth wave, the tsunami exhibited braided energy patterns that spread laterally across the ocean surface, showing that tsunami wave fields can be more intricate than expected.
• Dispersive behavior: Parts of the wave moved at slightly different speeds, creating trailing waves after the main crest. This dispersion had not been clearly observed at ocean-wide scales before.
• Wide spatial coverage: SWOT’s swath extended over tens of thousands of square kilometers, offering a continuous snapshot that traditional point measurements cannot match.
• Height and shape data: Scientists were able to measure real-time variations in tsunami height and shape, which are critical for refining forecast models that predict coastal impact.
• Model validation: Comparing SWOT’s observations with NOAA’s tsunami forecast models confirmed that the models were largely accurate, but also highlighted areas needing refinement for complex wave features.

Satellite observations like these are valuable not just for validating models after an event, but also for improving future predictions. Knowing how a tsunami wave evolves in the open ocean helps scientists understand how energy is distributed and how it might amplify or dissipate before reaching land.

Why This Matters for Coastal Safety

Tsunamis are among the most destructive natural hazards, capable of inundating coastal regions with little warning and catastrophic impact. Traditional early-warning systems rely on seismic readings (to detect the triggering earthquake) and ocean buoys (to measure wave characteristics). However, without detailed real-time data from across the wave field, forecasts have inherent uncertainties.

SWOT’s high-resolution snapshots offer a new dimension to tsunami science. By revealing the shape and energy distribution of the tsunami in the open ocean, researchers can:

• Improve forecast accuracy: More detailed initial conditions help numerical models more accurately simulate how tsunamis change as they travel toward coastlines.
• Enhance warning lead times: Continuous satellite data could supplement buoy networks, especially in remote ocean regions where in-situ measurements are sparse.
• Inform hazard assessment: Better understanding of energy dispersion could refine estimates of wave heights and arrival times at landfall locations.
• Support community preparedness: More precise and detailed hazard information can help emergency managers tailor evacuation orders and community responses.
• Advance scientific knowledge: Observing tsunami behavior at ocean-wide scales allows scientists to test and improve theoretical models of wave propagation and interaction with ocean dynamics.

The SWOT Mission and Its Broader Role

The SWOT mission has wider scientific objectives beyond tsunamis. Designed to map the heights of Earth’s surface water — from ocean currents to lakes and rivers — SWOT provides data that help researchers understand climate change impacts, water cycle dynamics, and ocean circulation patterns. Its KaRIn instrument measures the height of water bodies across wide swaths, generating rich datasets for global water monitoring.

Unlike satellites that capture images in visible wavelengths, SWOT’s radar interferometry technique detects the physical height of the water surface with great precision. This capability allows scientists to track subtle variations in water levels that are invisible to optical instruments — including small waves, ocean eddies, and long-wavelength sea surface features.

In the case of the 2025 Pacific tsunami, SWOT’s orbital pass happened to coincide with the tsunami’s propagation, offering a serendipitous opportunity that scientists are capitalizing on to push oceanographic understanding forward. Future satellite passes, coordinated with other observations, may help provide even more comprehensive views of ocean dynamics in extreme conditions.

The success of SWOT underscores the importance of international collaboration in Earth observation. NASA and CNES jointly operate the mission, combining expertise and data sharing to benefit not just scientific communities but also disaster management agencies around the world. As the satellite continues its operations, researchers expect more breakthroughs in understanding water systems — from coastal hazards to freshwater resources.

Conclusion

The first high-resolution, spaceborne capture of a tsunami by NASA and CNES’s SWOT satellite marks a significant breakthrough in ocean science and hazard forecasting. By revealing complex wave behavior across vast stretches of open water, SWOT has provided scientists with a new lens through which to observe and understand tsunami dynamics. These observations challenge traditional assumptions, enhance model validation, and have the potential to improve early-warning systems for vulnerable coastal regions. As satellite technology continues to advance, the fusion of spaceborne data with ground-based measurements will play an increasingly vital role in safeguarding communities and expanding our knowledge of Earth’s powerful ocean processes.