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Satellite Imagery Helping Tsunami Relief Effort
Satellite images are helping to target relief efforts in regions devastated by the Asian tsunamis of December 26. Maps like the one at right are based on vegetation loss, which at this resolution "is the clearest indication of where the damage is", says Christopher Small, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory.
The images may also yield clues about the shape and strength of the deadly tidal waves.
Plants reflect infrared light, so Small overlaid "before" and "after" images from an infrared camera on Landsat 7 to show where the waves had washed away trees and shrubbery.
The images will be sent to the United Nations and the World Bank so they can decide how to best get aid into damaged areas, Small said. Satellite imagery is especially important for remote areas, says Jian Lin, a marine geophysicist at the Woods Hole Oceanographic Institution in Massachusetts, US. "Without these techniques, those areas are very difficult to get into because the roads are often cut off," he told New Scientist.
The massive earthquake off the Indonesian island of Sumatra spawned massive ocean swells, which have killed an estimated 155,000 people and left millions more without clean water, food, or shelter.
Relief agencies are using satellite images to find the hardest-hit areas. High-resolution satellites, such as the commercial satellite QuickBird, focus in on relatively small regions to show details as small as 0.6 metres across. These dramatic images can be used to discern damage to individual buildings.
But satellites with lower resolution can provide a wider overview. NASA's Landsat 7 satellite, for example, images the entire globe in 180-kilometre swathes every 16 days, at a resolution of 30 metres. It passed over Sumatra's battered northern tip on December 29, and on Tuesday scientists produced a map showing the areas most affected by the flooding (see image).
The map at left is based on vegetation loss, which at this resolution "is the clearest indication of where the damage is", says Christopher Small, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory, New York.
The scientists say satellite images could also shed light on how the waves travelled through the Indian Ocean and with what force they reached the shore. At present, this process can only be modelled using computer simulations. Floating sea-level sensors just offshore measure ocean waves directly around many countries. But coverage from the sensors is "spotty", says Lin, so data from satellite images snapped during the tsunamis themselves can be used to show the waves' shape and speed.
Images taken later can reveal the waves' strength at various points along the coast. More powerful waves will reach higher terrain or further inland, says Small, so researchers can study wave power by comparing damage maps with maps of elevation.
Images from a range of satellites are now being collected into a central image bank for use by relief agencies. The Indian Ocean Tsunami Geospatial Information Service was launched on Sunday.
The Earth Institute at Columbia University is the world’s leading academic center for the integrated study of Earth, its environment and society. The Earth Institute builds upon excellence in the core disciplines—earth sciences, biological sciences, engineering sciences, social sciences and health sciences—and stresses cross-disciplinary approaches to complex problems. Through research, training and global partnerships, it mobilizes science and technology to advance sustainable development, while placing special emphasis on the needs of the world’s poor. For more information, visit www.earth.columbia.edu.