[CURITIBA, BRAZIL] A scientist's chance glimpse of a reflection in the atmosphere of the tsunami that devastated Japan earlier this year could lead to the first global tsunami monitoring system — which could also be faster and more efficient than the current systems.
Researchers from Brazil, France and the United States, using a highly sensitive, wide-angle camera at the top of Haleakala volcano in Hawaii, detected the 'airglow' signature in the atmosphere of the 11 March tsunami that devastated Japan, demonstrating that the genesis of a tsunami leaves a fingerprint in the ionosphere — an ionised zone of the atmosphere more than 80 kilometres up.
Tsunamis usually cause the sea level to rise rapidly by a few centimetres, which displaces the air immediately above it. This creates waves in the air that move quickly upward, eventually reaching and disturbing the ionosphere. Interaction with the charged ionosphere creates a faint red glow, the signature airglow that can be detected.
This effect was predicted in the 1970s, but little progress has been made since then on using these observation methods. The researchers presented their observations in a paper in Geophysical Research Letters last month (7 July).
"We have been studying the ionosphere since 1999, but we didn't expect to end up with a new method for tsunami detection," Jonathan Makela, an electrical engineer at the University of Illinois at Urbana-Champaign, United States, and the lead author of the paper, told SciDev.Net.
Currently tsunamis are detected by monitoring the sea surface level or the pressure of the water near the seabed. While this is efficient, it is limited to areas where adequate equipment is installed — the new finding could now lead to a global remote sensing system that would not need equipment on the ground.
"A new global system could be set up," said co-author Philippe Lognonné, from the Institute of Earth Physics of Paris, at Paris Diderot University in France. "We could detect tsunamis in zones deprived of geophysical monitoring, as well as tsunamis generated by effects other than quakes [such as volcanic eruptions and underwater landslides]."
Lognonné said that the new system would allow us to detect tsunamis well before what is possible with the current system.
The European Space Agency is evaluating the idea of taking a recording instrument on board one of its satellites for a demonstration mission — the instrument would cost €10 million (around US$14 million), according to Lognonné.
Makela said this system would not replace the current ones, but complement them to give a much wider monitoring capacity.
Victor Gallardo, a professor of oceanography at the University of Concepción, Chile, told SciDev.Net: "If it really works, I see advantages for a long country like Chile, where a repetitive, expensive tsunami alert system would be necessary.
"The installation of this technology in satellites should be a priority for the existing dedicated international organisations. Our scientific and engineering communities should examine this option very carefully and urgently".
John Largier, professor of coastal oceanography at the University of California, Davis, United States, who has been working on the use of radar for tsunami detection, said that airglow was "quite an amazing phenomenon … that may have value in providing some low-cost global coverage".
But he added: "I don't see how it will give the detail on wave amplitude and currents that can be obtained from data on the ocean itself".
See below for a video of the tsunami captured by the new method:
Geophysical Research Letters doi: 10.1029/2011GL047860 (2011)