High resolution altimetry reveals new characteristics of the December 2004 Indian Ocean tsunami

Abstract

[1] The Indian Ocean tsunami, which occurred on December 26, 2004, was the first to be clearly observed using satellite altimeters. The wave amplitude observed in deep-ocean by TOPEX and Jason-1 was close to 60 cm about 2 hours after the earthquake. Envisat crossed the tsunami wave 3h15 after the earthquake and measured a 35 cm wave. Even though it flew over the tsunami 7h20 after the earthquake, GFO still observed a wave close to 20 cm. To better extract the tsunami signal from altimeter measurements, a specific ocean variability mapping technique is used. This technique proves to be mandatory for discriminating tsunami waves from other ocean signals. Altimeter signals are then compared with those derived from the CEA (Commissariat à l'Energie Atomique) model outputs. For the first time with altimeter data, peculiar short wavelengths signals along Jason-1 and Envisat profiles have been detected from the analysis of 20-Hz altimeter measurements. Such high wavenumber signals can be explained by the dispersive propagation of tsunami waves. These observations highlight the essential role of satellite altimeter measurements to better understand and to improve models of tsunami wave propagation and dissipation.

Detection of Tsunamis from Changes in Ocean Surface Roughness

“…While not the focus of our study, SSH measurements allow us to identify the location of the leading edge of the tsunami. Detection of tsunamis in SSH measurements has been demonstrated in several previous studies (Okal et al, 1999;Ablain et al, 2006), although weak tsunamis generally remain obscured by background ocean variability. By utilizing satellite altimetry data, we are able to identify the location of the tsunami's leading edge in SSH measurements and test the concurrently measured σ 0 values for tsunami-induced changes in ocean surface roughness.…”

“…Of these four satellite altimeters, Jason-1 provides the earliest observations of the Sumatra-Andaman tsunami and has the most extensive records. Jason-1 encountered the leading edge of the tsunami 1 h 53 minutes after the earthquake (Ablain et al, 2006;Gower, 2007) at about 5°S in the Indian Ocean heading northeast on ascending pass 129 of cycle 109 (Fig. 1).…”

“…Satellite altimeters have also sampled several tsunamis over the past two decades. The satellite altimetry sea surface height (SSH) measurements of the Sumatra-Andaman tsunami were used by a number of authors to study the properties of the tsunami, its propagation and scattering from the coastline as well as to improve characterization of the seismic source of the tsunami, and to verify numerical models (Fine et al, 2005;Kulikov et al, 2005;Smith et al, 2005;Song et al, 2005;Titov et al, 2005;Ablain et al, 2006;Hirata et al, 2006;Kumar et al, 2006;Fujii & Satake, 2007;Gower, 2007;Hayashi, 2008;Hoechner et al, 2008;Sladen & Hebert, 2008). Detection of earlier weaker tsunamis in less extensive satellite altimetry SSH records is discussed by Okal et al (1999) and Zaichenko et al (2005).…”

Detection of the 2010 Chilean tsunami using satellite altimetry

“…Furthermore, by using only the cycle before the tsunami cycle, we can explore the possibility of using this simple filtering technique for real-time detection of a tsunami signal in SSH measurements. The second, more complex, filtering method is based on a specific mapping technique, first introduced by Ablain et al (2006). The method involves collecting 20 days of data before and after tsunami occurrence provided by all available altimeters (Jason-1, Jason-2, and Envisat).…”

“…Gower (2007) subtracted the smoothed average of SSH measured on previous and subsequent cycles to the tsunami cycle over the same pass. Ablain et al (2006) also demonstrated the utility of filtering with a more sophisticated technique based on ocean variability mapping. Both of these methods rely on measurements taken a significant amount of time after the tsunami has occurred, making them impractical to use in a real-time detection system.…”