Space-based system using GPS satellites can warn of incoming tsunami – ScienceDaily

A new study by an international team led by UCLA researchers shows that a new method for detecting tsunamis using existing Earth-orbiting GPS satellites could serve as an effective warning system for countries around the world.

The initial tsunami waves are a few centimeters high, but they nonetheless cause a disturbance in Earth’s upper atmosphere by forcing air up and creating a sound wave that amplifies as it rises higher.

This leads to a change in the ionosphere, at an altitude of 300 km above the Earth’s surface, as the electron density in the region decreases. This in turn affects the radio signals that GPS satellites send to GPS receivers on Earth, delaying or accelerating different parts of the signal, or changing the direction of the signal, depending on the frequency.

For the new study, published in the journal Natural Hazards and Earth System Sciences, researchers from UCL and universities in Japan have developed a new method for detecting this drop in electron density from modified GPS signals.

Looking at GPS data at the time of the devastating 2011 Tohoku-Oki earthquake and tsunami, they found that a tsunami warning could have been issued with confidence within 15 minutes of the earthquake—at least 10 minutes before the first earthquake . Tsunami hits the east coast of Japan.

They also found that it was possible to issue a warning using data from just 5% of Japan’s 1,200 GPS receivers – meaning the method could be used in countries with less GPS than Japan.

“Current tsunami warning systems are not as effective as they should be and often cannot accurately predict the height of the tsunami wave,” said Professor Serge Guillas (UCL Statistical Science and the Alan Turing Institute), senior author of the research. The Japanese warning of estimating the height of the wave, a better warning might have saved lives and lessened the widespread devastation that occurred, allowing people to reach higher ground and further from the sea.

“Our study, a joint effort by statisticians and astronomers, demonstrates a new, low-cost method for tsunami detection, as it builds on existing GPS networks, and can be implemented worldwide, complementing other methods of tsunami detection and improving the accuracy of warning systems.”

Lead author and PhD researcher Ryuichi Kanai (UCL Statistical Science and the Alan Turing Institute) said: “Our calculations indicate that wave size and shape can be inferred from turbulence in the ionosphere, so the next step in the research will be further investigation into this to see if The method could have been used to get more accurate predictions of the size and extent of a tsunami. From my experience working with the Japanese government in the past and seeing the damage caused by tsunamis, I believe that if this research comes to fruition, it will certainly contribute to saving lives.”

The researchers used statistical techniques to reconstruct the electron density drop in the atmosphere based on scattered points provided by GPS data, as well as to determine the uncertainty inherent in the modeling.

The researchers found that the sound wave generated by the initial rise in the water took about seven minutes to reach a height of 300 km in the ionosphere, and the electron density drop as a result can be detected via satellite signals within 10 to 15 minutes.

Tsunamis are low in deep water but can travel at a flying speed (up to 800 kilometers per hour in the deep sea) and when they enter shallow water, they slow down and grow in height.

Many current tsunami warning systems infer tsunamis from earthquakes, but this proposed method can be used to predict incoming tsunamis with non-seismic sources, such as landslides and volcanic eruptions.

While some tsunamis reach coasts in less than 10 minutes, the researchers noted that this method can also be used to predict second or third waves, helping to determine whether a tsunami warning should be canceled or maintained after the first wave.

The ionosphere extends from 48 km to 965 km above the Earth’s surface (where the Earth’s atmosphere meets space). The heat from the sun cooks the gases until they lose electrons (that is, they ionize), creating a sea of ​​charged particles that includes an abundance of free electrons.

The study was conducted by researchers at the University of California, The Alan Turing Institute, Tokai University, and Shizuoka University, Japan. It is supported by the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT), the University of Tokyo Earthquake Research Institute, the UK Engineering and Physical Sciences Research Council (EPSRC), and the Japan Science and Technology Agency (JST).

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