Tsunami airglow signature could lead to early detection system (w/Video)

Jul 14, 2011
The red line represents the location of the ocean-level tsunami at the time of the image. Credit: Jonathan Makela

Researchers at the University of Illinois have become the first to record an airglow signature in the upper atmosphere produced by a tsunami using a camera system based in Maui, Hawaii.

The signature, caused by the March 11 that devastated Japan, was observed in an airglow layer 250 kilometers above the earth's surface. It preceded the tsunami by one hour, suggesting that the technology could be used as an in the future. The findings were recently published in the peer-reviewed .

The observation confirms a theory developed in the 1970s that the signature of tsunamis could be observed in the upper atmosphere, specifically the ionosphere. But until now, it had only been demonstrated using broadcast by satellites.

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The three panels represent the data filtered using different passbands to highlight waves of different periods. The red line is the location of the ocean-level tsunami at the time of each image. The moving dots are measurements of ionospheric electron density made using GPS receivers located on the islands of Hawaii. Credit: Jonathan Makela

"Imaging the response using the airglow is much more difficult because the window of opportunity for making the observations is so narrow, and had never been achieved before," said Jonathan Makela, a professor of electrical and at the University of Illinois at Urbana-Champaign. "Our camera happened to be in the right place at the right time."

Tsunamis can generate appreciable wave amplitudes in the – in this case, the airglow layer. As a tsunami moves across the ocean, it produces atmospheric gravity waves forced by centimeter-level surface undulations. The amplitude of the waves can reach several kilometers where the neutral atmosphere coexists with the plasma in the , causing perturbations that can be imaged.

On the night of the tsunami, conditions above Hawaii for viewing the airglow signature were optimal. It was approaching dawn (nearly 2 am local time) with no sun, moon or clouds obstructing the view of the night sky.

Along with graduate student Thomas Gehrels, Makela analyzed the images and was able to isolate specific wave periods and orientations. In collaboration with researchers at the Institut de Physique du Globe de Paris, CEA-DAM-DIF in France, Instituto Nacional de Pesquisais Espaciais (INPE) in Brazil, Cornell University in Ithaca, NY, and NOVELTIS in France, the researchers found that the wave properties matched those in the ocean-level tsunami measurements, confirming that the pattern originated from the tsunami. The team also cross-checked their data against theoretical models and measurements made using GPS receivers.

Makela believes that camera systems could be a significant aid in creating an early warning system for tsunamis.

Currently, scientists rely on ocean-based buoys and models to track and predict the path of a tsunami. Previous upper atmospheric measurements of the signature relied on GPS measurements, which are limited by the number of data points that can be obtained, making it difficult to create an image. It would take more than 1,000 GPS receivers to capture comparable data to that of one camera system. In addition, some areas, such as Hawaii, don't have enough landmass to accumulate the number of GPS units it would take to image horizon to horizon.

In contrast, one camera can image the entire sky. However, the sun, moon and clouds can limit the utility of camera measurements from the ground. By flying a on a geo-stationary in space, scientists would be able to avoid these limitations while simultaneously imaging a much larger region of the earth.

To create a reliable system, Makela says that scientists would have to develop algorithms that could analyze and filter data in real-time. And the best solution would also include a network of ground-based cameras and GPS receivers working with the satellite-based system to combine the individual strengths of each measurement technique.

"This is a reminder of how interconnected our environment it," said Makela, who is also a researcher in the Coordinated Science Laboratory at Illinois. "This technique provides a powerful new tool to study the coupling of the ocean and atmosphere and how tsunamis propagate across the open ocean."

Explore further: Wastewater injection is culprit for most quakes in southern Colorado and northern New Mexico

Provided by University of Illinois College of Engineering

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Husky
not rated yet Jul 14, 2011
impressive work! not only confirming a theory but providing an early warning tool, maybe the disturbance of the ionosphere would not only cause glow but certain noise-interference of manmade radiosignals we send? if so computers would be able to filter it out and triangulate it
lengould100
not rated yet Jul 14, 2011
Do you mean that perhaps a passing tsunami might have an immediate effect on the propagation of "shortwave" radio transmissions by temporarily changing the position of the ionosphere? Neat idea. I wonder if the effect could be measured?
Graeme
not rated yet Jul 17, 2011
If the ionized region gets pushed up several kilometers this would cause a big shift in where the shortwave radio signals were reflected from and a phase shift of dozens to a hundred wavelengths, This would cause very dramatic change in fading rate over whatever time the change took. At 250 km this would be a night time only effect, but presumably there is a smaller bump at lower levels of the atmosphere, so radio signals would also change in the day.