Abstract:
The initial tsunami waves resulting from the undersea earthquake that occurred
at 00:58:53 UTC on 26 December 2004 off the island of Sumatra, Indonesia, took
a little over 2 hours to reach the teardrop-shaped island of Sri Lanka.
Additional waves continued to arrive for many hours afterward. At approximately
05:15 UTC, as NASA's Terra satellite passed overhead, the Multi-angle Imaging
... SpectroRadiometer (MISR) captured this image of deep ocean tsunami waves about
30-40 kilometers from Sri Lanka's southwestern coast. The waves are made
visible due to the effects of changes in sea-surface slope on the reflected
sunglint pattern, shown here in MISR's 46 degrees forward-pointing camera.
Sunglint occurs when sunlight reflects off a water surface in much the same way
light reflects off a mirror, and the position of the Sun, angle of observation,
and orientation of the sea surface determines how bright each part of the ocean
appears in the image. These large wave features were invisible to MISR's nadir
(vertical-viewing) camera. The image covers an area of 208 kilometers x 207
kilometers.
Since the greatest impact of the tsunami was generally in an east-west
direction, the havoc caused by the tsunami along the southwestern shores of Sri
Lanka was not as severe as along the eastern coast, though there was still
substantial damage in this region -- as evidenced by the brownish debris in the
water -- because tsunami waves can diffract around land masses. The ripple-like
wave pattern evident in this MISR image roughly correlates with the undersea
boundary of the continental shelf. This surface manifestation is likely to be
caused by interaction of deep waves with the ocean floor, rather than by the
more usually-observed surface waves driven by winds. It is possible that this
semi-concentric pattern represents wave reflection from the continental land
mass; however, a combination of wave modeling and detailed bathymetric data is
required to fully understand the dynamics. Examination of other MISR images of
this area, taken under similar illumination conditions, has not uncovered any
surface patterns resembling those seen here. This image is an example of how
MISR's multiangular capability provides unique information for understanding
how tsunamis propagate.
The Multi-angle Imaging SpectroRadiometer observes the daylit Earth
continuously and every 9 days views the entire globe between 82 degrees north
and 82 degrees south latitude. These data products were generated from a
portion of the imagery acquired during Terra orbit 26720 and utilize data from
within blocks 85 to 86 within World Reference System-2 path 142.
MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena,
CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is
managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division
of the California Institute of Technology. 
