Satellites can spot the leading edge of a tsunami, U.S. government researchers said on Wednesday in a study that might lead to better ways of detecting the giant waves and get people out of their way, Reuters reported.
They went back and looked at satellite images in the Indian Ocean as the December 2004 tsunami raced across to destroy coastlines in Thailand, Sri Lanka and elsewhere. They found clear patterns in the water.
"We've found that roughness of the surface water provides a good measure of the true strength of the tsunami along its entire leading edge," Oleg Godin of the National Oceanic and Atmospheric Administration in Boulder, Colorado, said in a statement.
"This is the first time that we can see tsunami propagation in this way across the open ocean."
A giant earthquake in Indonesia triggered the 2004 tsunami, which killed more than 228,000 people.
Governments have since rushed to complete an early warning system of mid-ocean buoys that would detect such waves as they pass by. But such a system is imperfect and might miss areas, especially as the buoys cannot be placed everywhere.
Tsunamis can only usually be seen when they enter shallow water. In the depths of an ocean, the water they displace barely shows -- although this tiny movement can also be detected by satellites.
The satellites that can do this, however, do not cover all the world's seas.
Godin's team found that tsunamis crossing the open ocean stir up and darken the surface waters along the leading edge of the wave. Many ordinary satellites can detect the dark pattern, they reported in the journal Natural Hazards and Earth System Sciences.