NASA's GUARDIAN System Catches Tsunamis Before They Strike

The Minutes That Matter in Tsunami Warning

When a major undersea earthquake generates a tsunami, the window between detection and landfall can be as little as fifteen minutes for communities near the epicenter. Every additional minute of warning time translates directly to lives saved — people who reach higher ground, who get clear of the inundation zone, who survive what otherwise becomes a death toll. NASA has been developing a technology that could add meaningful minutes to that window by detecting the atmospheric signature of a tsunami before conventional ocean-floor sensor networks can compile and transmit their data.

The technology is called GUARDIAN — GNSS Upper Atmospheric Real-time Disaster Information and Alert Network — and it works on a principle that would have seemed improbable until recently. When a tsunami propagates across the ocean, it creates pressure waves in the atmosphere above it. These atmospheric waves propagate upward as well as horizontally, reaching the ionosphere — the electrically charged layer of the upper atmosphere — where they create measurable disturbances in electron density that affect the propagation of GPS signals passing through the layer.

How GUARDIAN Detects the Invisible Wave

The GPS constellation that enables navigation on Earth also functions, in the GUARDIAN concept, as an accidental tsunami sensor. Every GPS receiver on Earth is continuously receiving signals that pass through the ionosphere. A tsunami-generated atmospheric pressure wave distorts the ionosphere slightly but measurably, introducing anomalies into the GPS signal propagation data that trained algorithms can detect and distinguish from background ionospheric variability.

Because GPS signals are received simultaneously by thousands of ground stations and billions of consumer devices worldwide, the GUARDIAN system can aggregate ionospheric disturbance data from a dense, globally distributed sensor network without deploying any dedicated hardware. The processing challenge is distinguishing genuine tsunami signals from the substantial background noise in ionospheric data — a problem NASA researchers have addressed through machine learning models trained on historical tsunami events and their characteristic ionospheric signatures.

A new data visualization released by NASA this week demonstrates GUARDIAN's detection capability using the 2022 Hunga Tonga-Hunga Ha'apai volcanic eruption and associated tsunami as a test case. The visualization shows how the atmospheric pressure wave from that event propagated upward through the atmosphere and created detectable ionospheric disturbances that spread ahead of the physical tsunami wave in the ocean below.

Minutes of Extra Warning Time

In the Hunga Tonga event, GUARDIAN's ionospheric detection would have provided approximately 10 to 15 minutes of additional warning time compared to the seafloor pressure sensors of the DART network operated by NOAA. For communities in Hawaii and along the US West Coast, DART provides the primary tsunami warning data. For communities closer to the source — including Pacific island nations — the combination of short propagation times and DART network density limitations means that any additional warning is particularly valuable.

The extra warning time comes from the physics of wave propagation: acoustic and atmospheric pressure waves from the tsunami source travel at the speed of sound in the atmosphere, which is faster than the speed of the tsunami wave in the ocean. GUARDIAN captures the atmospheric signature, which races ahead, rather than waiting for the physical wave to reach a seafloor pressure sensor.

NASA is currently working with NOAA, which operates the official US tsunami warning system, on integration protocols that would incorporate GUARDIAN data into operational warning alerts. The two agencies have established a joint working group that is evaluating how GUARDIAN detections should be weighted alongside traditional seafloor sensor data in the warning decision process.

Expanding the Sensing Capability

The ionospheric sensing principle that GUARDIAN applies to tsunami detection has potential applications across other geophysical hazard domains. Volcanic eruptions, large explosions, and major earthquakes all generate atmospheric pressure waves with characteristic ionospheric signatures. The same global GPS infrastructure that enables GUARDIAN's tsunami detection could be applied to these other hazards with appropriate algorithm development.

NASA is also exploring whether the sensitivity of GPS-based ionospheric sensing can be enhanced by deploying a network of dedicated GPS reference stations in regions currently underserved by the sensor density of the existing ground receiver network. The Pacific island region, where many at-risk communities are located, has relatively sparse GPS ground station coverage compared to the continental US and Europe, limiting the resolution of ionospheric monitoring in the area of greatest tsunami risk.

The GUARDIAN team has published their detection methodology and is making the underlying software tools available to the international scientific community, with the goal of enabling parallel development efforts in countries with independent space programs and GPS ground networks. Japan, which has the world's densest GPS ground station network and faces some of the world's most severe tsunami risk, has already begun evaluating GUARDIAN's methodology through its own national research programs.

Part of a Broader NASA Disaster Monitoring Mission

GUARDIAN represents one of several NASA programs that leverage existing space infrastructure for terrestrial disaster monitoring and warning applications. NASA's ARIA program uses synthetic aperture radar satellite data to map earthquake damage in near-real-time, while the GRACE-FO satellite mission monitors groundwater depletion and has been applied to drought early warning applications. The common thread across these programs is the repurposing of space-based scientific infrastructure for practical societal benefit — a mandate that NASA has increasingly emphasized as a core part of its mission alongside basic science and human exploration.

This article is based on reporting by NASA. Read the original article.