Airglow signature imaging could lead to tsunami early warning system
Urbana, IL--University of Illinois at Urbana-Champaign researchers are the first to have imaged an airglow signature 250 km above the surface of the earth that was produced by the tsunami that followed the March 11 earthquake in Japan. Using a camera system based in Maui, Hawaii, the recorded signature preceded the tsunami by one hour, suggesting that the technology could be used as an early-warning system in the future.
The observation, detailed recently in Geophysical Research Letters, 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 radio signals broadcast by satellites. "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, an associate professor of electrical and computer engineering and researcher in the Coordinated Science Laboratory at the University of Illinois. "Our camera happened to be in the right place at the right time."
Tsunamis can generate appreciable wave amplitudes in the upper atmosphere--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 ionosphere, 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 2:00 a.m. local time) with no sun, moon or clouds obstructing the view of the night sky.
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.
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.
SOURCE: University of Illinois at Urbana-Champaign; http://engineering.illinois.edu/news/2011/07/13/tsunami-airglow-signature-could-lead-early-detection-system