Natural Hazards and Earth System Science www.nat-hazards-earth-syst-sci.net 1561-8633 1684-9981 9 4 2009 10.5194/nhess-9-1135-2009 http://www.nat-hazards-earth-syst-sci.net/9/1135/2009/ http://www.nat-hazards-earth-syst-sci.net/9/1135/2009/nhess-9-1135-2009.html http://www.nat-hazards-earth-syst-sci.net/9/1135/2009/nhess-9-1135-2009.pdf 1135 1147 2009-07-16 Variations in sea surface roughness induced by the 2004 Sumatra-Andaman tsunami O. A. Godin oleg.godin@noaa.gov V. G. Irisov R. R. Leben B. D. Hamlington G. A. Wick Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA NOAA/Earth System Research Laboratory, Boulder, CO 80305-3328, USA ZelTechnology LLC, Boulder, CO 80305, USA Colorado Center for Astrodynamics Research, University of Colorado, Boulder, CO 80309, USA Observations of tsunamis away from shore are critically important for improving early warning systems and understanding of tsunami generation and propagation. Tsunamis are difficult to detect and measure in the open ocean because the wave amplitude there is much smaller than it is close to shore. Currently, tsunami observations in deep water rely on measurements of variations in the sea surface height or bottom pressure. Here we demonstrate that there exists a different observable, specifically, ocean surface roughness, which can be used to reveal tsunamis away from shore. The first detailed measurements of the tsunami effect on sea surface height and radar backscattering strength in the open ocean were obtained from satellite altimeters during passage of the 2004 Sumatra-Andaman tsunami. Through statistical analyses of satellite altimeter observations, we show that the Sumatra-Andaman tsunami effected distinct, detectable changes in sea surface roughness. 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