The GPS signal can detect tsunamis


A new method to detect tsunamis using the existing GPS satellites orbiting the Earth it could serve as an effective warning system for countries around the world. This is the conclusion of a new study conducted by an international team led by researchers from UCL (University College London).

The initial waves of the tsunami are usually a few centimeters high, but they nevertheless disturb the Earth’s upper atmosphere by pushing the air upwards and creating an acoustic wave that amplifies as it rises. This results in a modification of the ionosphere, 300 km above the surface of the Earth, wherein the electron density of the area is reduced. This, in turn, affects radio signals sent from GPS satellites to GPS receivers on the ground, slowing down or speeding up different parts of the signal, or changing the direction of the signal, depending on the frequency.

For the new study, published in Natural Hazards and Earth System Sciences, researchers from UCL and Japanese universities have developed a new way to detect this drop in electronic density of modified GPS signals. By examining 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, that is- to say at least 10 minutes before the first tsunami reach the east coast of Japan.

Natori, devastated by the tsunami in Japan (Photo: Reuters)

They also found that a warning could have been issued using data from only 5% of Japan’s 1,200 GPS receivers, which means that the method could be used in countries with a less dense GPS network than Japan. Professor Serge Guillas (UCL Statistical Science and the Alan Turing Institute), lead author of the paper, said in a statement: “Current tsunami warning systems are not as effective as they should be because they often cannot accurately predict the height of a tsunami. vague.

In 2011, the Japanese warning system underestimated the height of the wave. A better warning could have saved lives and reduced the widespread destruction that has occurred, allowing people to reach higher lands farther from the sea.” Our study, a joint effort of statisticians and scientists from the space, demonstrates a new method of tsunami detection that is inexpensive because it relies on existing GPS networks and could be deployed worldwide, complementing other tsunami detection methods.” and improve the accuracy of warning systems”.

The researchers used statistical techniques to reconstruct the electron density depression in the atmosphere from scattered points provided by GPS data, as well as to quantify the uncertainty inherent in the modeling. The acoustic wave caused by the initial rise of the water took about seven minutes to reach 300 km height in the ionosphere and the resulting decrease in electron density could be detected by satellite signals in 10 to 15 minutes, the researchers found.

Terror in the middle of the tsunami in Japan.
Terror in the middle of the tsunami in Japan.

Tsunami waves are weak in deep water, but can travel at jet speed (up to 800 km/h in deep water), and as they enter shallower water they slow down and increase in height. Many existing tsunami warning systems infer tsunami waves from earthquakes, but this proposed method could be used to predict incoming tsunamis with sources other than earthquakes, such as landslides and volcanic eruptions. .

Yes OK some tsunamis reach land in less than 10 minutesthe researchers noted that the method could also be used to predict the second or third wave, 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 (i.e. they become ionized), creating a sea of ​​charged particles that includes a large number of free electrons.

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