Tsunami Wave Effects Glimpsed from Spaceby Terri Gregory
Madison, WI, December 29—Even from space, wave patterns are apparent in this image taken by an instrument on NASA’s research satellite, Terra, about 1000 miles up from the terrible human drama unfolding along coasts in the Indian Ocean. At the University of Wisconsin-Madison, meteorologist and data specialist David Santek in the Space Science and Engineering Center (SSEC) retrieved these images from NASA’s data banks, freely accessible to scientists and others around the world. He processed and enhanced the raw images, using the center’s computer system called the Man computer Interactive Data Access System (McIDAS for short), to clearly show every bit of information.
Oceanographer Professor Arne Winguth of UW-Madison’s Department of Atmospheric and Oceanic Sciences said that wave patterns would be visible only close to land. The tsunami wave builds gradually, from less than an inch near the earthquake to the gigantic 30–50 foot high waves that have engulfed coastal villages and seaside resorts.
The image to the left of the pair shows the placid Indian Ocean near Sri Lanka, at the southern tip of India, one week before the tsunami. The image to the right, taken within 2 hours after the tsunami hit on Sunday, December 26, shows churning that may be a mixture of gigantic waves rebounding from land and the shallow water shelf that surrounds the island. According to Winguth, the satellite does not detect waves on the ocean, but rather changes in the composition of the ocean water. The tsunami disrupted the sediment in the shallow water that is transported to near the surface, appearing wave-like in the picture.
At its Direct Broadcast Facility, SSEC receives, archives and lends data from the MODerate-resolution Imaging Spectroradiometer on two of NASA’s earth observing satellites, Terra and Aqua. Project manager Liam Gumley produced a true color image showing the same area as Santek’s enhanced images. It is now on the MODIS Gallery Web site at http://www.ssec.wisc.edu/~gumley/modis_gallery/. Some turbidity is seen in the ocean. The McIDAS enhancement shows detail unavailable to most of us, making it useful in research.
In Madison, the antenna tracking the MODIS instrument can see only images of North America, from as far north as Hudson Bay to as far south as the Yucatan Peninsula in Mexico. You can find MODIS imagery of North America on the Web at http://www.ssec.wisc.edu/data/polar.html