NASA/French Satellite Data Reveal New Details of Tsunami
For the first time, orbiting satellites have observed and measured a
major tsunami event in open ocean, the Indian Ocean tsunami that
resulted from the magnitude 9 earthquake southwest of Sumatra on
December 26. The measurements are of tremendous value to
researchers worldwide and will aid our understanding of these
events.
U.S. and French teams working in parallel with altimetry data from
the joint NASA/French Space Agency Jason and Topex/Poseidon
oceanography satellites have independently confirmed the satellites'
measurements of the height of the tsunami waves as they radiated
from the earthquake's epicenter. The satellites flew over the Bay
of Bengal about 150 kilometers (93 miles) apart approximately two
hours after the quake.
"These two satellites make only about 13 Earth revolutions daily,
with each orbit passing over the Earth approximately 3,000
kilometers (1,864 miles) away from its last," said Dr. Philip
Callahan of NASA's Jet Propulsion Laboratory, Pasadena, Calif.
Callahan has been searching for tsunami signals in satellite radar
altimeter data since Topex/Poseidon's launch in 1992. "There is a
very low probability of capturing observations in any given location
within two hours of an event like this. The fact that Jason
captured the tsunami's signals is serendipitous, but is nevertheless
a major boon for oceanographers," he said.
"The observations made by Jason and Topex/Poseidon are unique and of
tremendous value for testing and improving tsunami computer models
and developing future tsunami early warning systems," said JPL's Dr.
Lee-Lueng Fu, Jason and Topex/Poseidon project scientist. "The
satellite altimeter data currently take a minimum of five hours to
process, so they cannot provide early warning of such events," said
Fu. Dr. Callahan received the Jason data the morning of December
27.
The new images are available online at:
http://photojournal.jpl.nasa.gov/catalog/PIA07219
The main figure displays changes in sea surface height from previous
observations made along the same ground track 20 to 30 days before
the earthquake, showing the signals of the tsunami waves. The inset
is a computer model of simulated changes in sea surface height
created by Kenji Satake of the National Institute of Advanced
Industrial Science and Technology, Japan. It provides a basin-wide
perspective for interpreting the Jason and Topex/Poseidon satellite
observations, which are in good agreement with the model.
The satellites recorded a maximum sea surface elevation gain
(deviation from normal) of 50 centimeters (1.6 feet) on the open
ocean about 1,200 kilometers (746 miles) south of Sri Lanka at the
leading crest of a tsunami wave raging out of the Bay of Bengal. It
was followed by a trough of sea surface depression of 40 centimeters
(1.3 feet) below normal. The distance from one wave crest to the
next was about 800 kilometers (500 miles). The first wave was
followed by a second with a crest height of 40 centimeters (1.3
feet) above normal. Near the northern end of the Bay, two waves
with crest heights of 40 centimeters (1.3 feet) and 20 centimeters
(0.66 feet) above normal were approaching the coasts of Myanmar.
Spreading across the Bay of Bengal from the earthquake zone offshore
from Western Sumatra, these tsunami waves eventually reached shallow
waters along the coasts of Sumatra, Sri Lanka, Thailand and Southern
India. Their open ocean speeds reduced from that of a jet plane,
800 kilometers (500 miles) per hour, to about 32 kilometers (20
miles) per hour, building the open ocean wave heights of 0.5 meters
(1.6 feet) or less to walls of water up to 10 meters (33 feet) high
with great destructive power.
Jason and Topex/Poseidon are collaborative satellite missions of
NASA and the French Space Agency, Centre National d'Estudes
Spatiales. The primary objectives of the two missions are to make
long-term measurements of the height of the world's sea surface to
better understand ocean circulation and its effects on climate.
"The information on sea surface height from these satellites has
many other applications, and can be used to aid navigation, offshore
operations, hurricane forecasting, fisheries, etcetera," said Dr.
Yves Menard, Jason and Topex/Poseidon project scientist at the
Centre National d'Estudes Spatiales. "The detection of these
tsunami waves provides yet another demonstration of the important
value of satellite radar altimeter observations."
NASA and the French Space Agency are working with the National
Oceanic and Atmospheric Administration and the European Organization
for the Exploitation of Meteorological Satellites to develop the
next radar altimeter mission, the Ocean Surface Topography Mission,
targeted for launch in 2008. It will make radar altimeter
measurement a routine operation of those organizations in the
future.
Additional information is available at:
http://sealevel.jpl.nasa.gov/ and
http://www.jason.oceanobs.com/html/portail/general/welcome_uk.php3
.
-end-
Date: Tue, 11 Jan 2005 18:48:58 -0800
Subject: NASA/French Satellite Data Reveal New Details of Tsunami
From: "NASA Jet Propulsion Laboratory"
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Alan Buis (818) 354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Eliane Moreaux (011) 33-5-61-27-33-44
Centre National d'Estudes Spatiales, Toulouse, France
NEWS RELEASE: 2005-013 January 11, 2005