The Indian Ocean Tsunami of December 26, 2004, Observed by Multi-satellite Altimetry.
Michaël Ablain(1) , Joël Dorandeu(1) , Joël Dorandeu(1) , Pierre-Yves Le Traon(2) , and Patrick Vincent(3)
8-10 rue Hermes, Parc Technologique du Canal,
31526 Ramonville Saint-Agne,
(2) IFREMER (Brest), Centre de Brest, B.P. 70 29280 Plouzané, France
(3) IFREMER, 155, rue Jean-Jacques Rousseau, 92138 Issy-les-Moulineaux Cedex, France
On December 26, 2004, at 0h59 p.m. UTC, an Indian Ocean earthquake with a magnitude of 9 generated a strong tsunami that produced huge waves at the coasts. They devastated the shores of all countries close to the Bengal Gulf with wave heights of up to 15 m.
Until then, tsunami observations by satellite altimeters had not been significant. But due to its intensity and its large area, the Indian Ocean tsunami was the first one detectable by TOPEX, Jason-1, Envisat and GFO satellites together. The wave amplitude observed in deep-ocean by TOPEX and Jason-1 was close to 60 cm when both satellites overflew the tsunami 2 hours after the earthquake. Envisat crossed the tsunami wave 3h15 later and measured a 30 cm wave. Finally, though GFO overflew the tsunami 7h20 later, it observed a wave close to 20 cm.
In order to better analyse the tsunami signal along satellite passes, we used a dedicated ocean variability mapping technique in order to decorrelate signals due to the tsunami and signals due to the ocean, such as mesoscale. First, altimeter observations and model outputs provided by CEA (Commissariat à l’Enérgie Atomique) have been compared with good accuracy. Then, particular signals with wavelengths between 20 and 30 km could be evidenced along Jason-1 and Envisat profiles. They could be attributed to the tsunami according to the theory of wave propagation in dispersive medium.
These observations of tsunami waves in deep ocean highlight the essential role of satellite altimeter measurements for improving the modelisation of tsunami wave propagation.