Tsunamis triggered by earthquakes, undersea volcanoes and other earth-shaking forces can devastate coastal communities. And when it comes to providing early warning, every second counts. Scientists at NASA’s Jet Propulsion Laboratory are testing a new approach to detect – from the far reaches of the atmosphere – the ocean’s most dangerous waves.
An experimental monitoring system called GUARDIAN (GNSS Upper Atmospheric Real-time Disaster Information and Alert Network) uses data from GPS clusters and other satellites to search for paths orbiting our planet. Collectively, these clusters are known as Global Navigation Satellite Systems, or GNSS. Their radio signals travel to hundreds of scientific ground stations around the world, and this data is processed by JPL’s Global Differential GPS (GDGPS) network, which improves real-time position accuracy to within a few inches (roughly 10 centimeters).
The new system sifts through signals and looks for clues that a tsunami has occurred somewhere on Earth. How does it work? During a tsunami, many square miles of the ocean’s surface can rise and fall almost simultaneously, displacing significant amounts of air above it.
Displaced air ripples in all directions in the form of low-frequency sound and gravity waves. Within minutes, these vibrations reach the uppermost layer of the atmosphere: the sun-boiled, electrically charged ionosphere. The subsequent collision of pressure waves with charged particles can very slightly distort signals from nearby navigation satellites.
The fastest monitoring tool of its kind
The technology is still maturing, said Martire, who co-chairs a working group within the UN’s International Committee on GNSS that is exploring the use of navigation satellite systems to improve early warning strategies. Currently, GUARDIAN output must be interpreted in near real time by experts trained to identify tsunami symptoms.
But it is already one of the fastest monitoring tools of its kind: Within 10 minutes, it can create a kind of picture of a tsunami that has reached the ionosphere. And it could potentially provide up to an hour’s warning depending on the distance of the tsunami’s origin from the coast.
“We envision that GUARDIAN will one day complement existing land and ocean instruments such as seismometers, buoys, and tide gauges, which are highly efficient but lack systematic coverage of the open ocean,” says Siddharth Krishnamoorthy, also part of the JPL development team. . Scientists associated with the NASA Disasters program are currently using ground-based instruments on GNSS stations for faster tsunami detection.
“When a large earthquake occurs near the ocean, we want to quickly know the magnitude and characteristics of the earthquake to understand the likelihood that a tsunami will form, and we want to know whether a tsunami has actually formed,” said Gerald Bawden. , program scientist for the Earth’s surface and interior at NASA Headquarters in Washington.
“Today there are two ways to tell if a tsunami was generated before it hit land – NOAA DART buoys and GNSS-ionosphere observations.” There are a limited number of buoys and they are very expensive, so systems like GUARDIAN have the potential to complement current warning systems.”
Right now, the GUARDIAN team is focusing on the geologically active Pacific Ring of Fire. About 78% of the more than 750 confirmed tsunamis between 1900 and 2015 occurred in this region, according to a historical database maintained by the National Oceanic and Atmospheric Administration (NOAA). GUARDIAN currently monitors just over half of the region of interest in the Pacific.
The GUARDIAN team is developing a website that will allow experts to examine the state of the ionosphere in near real time by studying the interconnection of individual satellite stations in the GNSS network. Users can access data from about 90 stations around the Pacific Ring of Fire and discover interesting signals within minutes of the event. The team’s goal is to expand coverage and improve the system to the point where it could automatically flag tsunamis and other hazards, including volcanic eruptions and earthquakes.
