Radar satellites capture tsunami wave height
Mar 20, 2009 I Recent Tsunamis.
A pair of satellites that happened to be over the Indian Ocean just after the massive Sumatran earthquake on 26 December have captured the only measurements of the tsunamis’ height in deep water. The images will help improve future forecasts of the deadly waves.
The satellites did not observe coastal areas. But for eight minutes, they used radar to measure the sea level along a 3000-kilometre-long track of ocean. This image of the bay as the tsunami rolled through it provides a unique and valuable continuous measure of the waves. In contrast, the floating sensors suggested as part of any future early-warning system can only provide measurements at single points.
The satellites saw the first two wavefronts produced by the main quake, spaced 500 to 800 kilometres apart. These waves reached a maximum height of 50 centimetres in the open ocean, only reaching their full devastating height when entering the shallow waters of the coast.
By comparison, wind-driven waves typically reach 10 metres. However, these waves only involve water close to the ocean surface and are separated by at most several hundred metres.
Tsunami waves have a very deep reach indeed - 4000 metres or more. “These waves involve the entire depth of the ocean. Their energy is thousands of times more than a monster storm, they speed through the water as fast as jet airliners.
The key number in the modelling is wave height in deep water, as this indicates energy, and that is exactly what the radar recorded. Fu adds that, because the waves take time to travel to land, “when you see waves in the open ocean this large, you have time to warn people on the coast