Oct. 13, 2000 Emergency food supplies being rushed to victims of the current flooding in Southeast Asia are being planned with the help of a new type of image from NASA's Terra spacecraft and a unique global flood monitoring system funded by NASA.
With new composite surface images from Terra released last month, Robert Brakenridge of Dartmouth College (Hanover, N.H.) produced maps showing the precise locations of flooded areas along the Mekong River. Hundreds of thousands of people have been displaced in the region by the worst flooding since 1961. These maps are being used by United Nations World Food Program staff to pinpoint the worst-hit areas.
"We get a dramatic increase in our mapping accuracy with the new 8-day composite images from the MODIS instrument onboard Terra," says Brakenridge. This new data product was released to the scientific community in August by the EROS Data Center in Sioux Falls, South Dakota, which is part of NASA's Earth Observing System Data and Information System. Images were available from early June at the onset of the Southeast Asia floods.
Before the early 1990s, mapping of flooded lands was limited to occasional aerial photography surveys of specific floods. Brakenridge and colleagues at Dartmouth used images from a spaceborne radar on the European ERS-1 satellite to produce some of the first satellite flood maps in 1993 of the extensive flooding in the upper Mississippi River valley that year.
Brakenridge, a fluvial geomorphologist in Dartmouth's geography department, began work on a global flood monitoring system in 1996 that would convert available satellite imagery into precise geographic information on flooded areas that could be distributed to disaster relief agencies through the World Wide Web. The result was the Dartmouth Flood Observatory.
"The Observatory is the first system for global flood monitoring using remote sensing," says Brakenridge. "We can use almost any data source and incorporate it into a global data base of flood-prone areas." The system uses satellite images from the Advanced Very High Resolution Radiometer on National Oceanic and Atmospheric Administration satellites, the Canadian Radarsat, NASA's Landsat 7, and now Terra.
The Dartmouth Flood Observatory was developed with funding from NASA's Earth Observing System (EOS) program, which is managed at Goddard Space Flight Center. EOS is a program of multiple spacecraft missions and interdisciplinary science investigations to understand global climate change. Flood maps from the Dartmouth system have been used to aid relief efforts in Honduras after Hurricane Mitch in 1998 and in the Carolinas after Hurricane Floyd in 1999.
"MODIS has made an enormous difference in our flood mapping," says Brakenridge. "MODIS can image most of the world every day and it views a very wide area." The images are much more detailed than other readily available wide-area images. Terra was launched by NASA in December 1999.
The frequent heavy cloud cover over Southeast Asia makes it difficult to regularly see the surface and flooded areas, says Brakenridge. To overcome this problem, eight MODIS images from consecutive days are blended together to produce one image that combines all the cloud-free views of the surface. This new image product provides a look at how much floods rise or fall nearly every week.
Observations of floods in a region over successive years help disaster relief agencies like the United Nations unequivocally identify the largest flood events and allocate limited aid resources accordingly.
"The MODIS maps are proving really useful to us," said Mahadevan Ramachandran, the United Nations World Food Program regional vulnerability analysis and mapping officer in Phnom Penh, Cambodia. "In areas like Cambodia and Laos where there are weak data collection systems on the ground, the MODIS data will be our first-hand information to identify the areas we need to visit and assess for ourselves."
Ramachandran compares the new MODIS maps with 1999 flood maps to pinpoint hardest hit by the current flooding. "We overlay the MODIS maps with maps of crop production, poverty level, and land cover and land use derived from Landsat images to design our food aid relief efforts." The World Food Program is planning to feed nearly 500,000 people in Cambodia starting this month and continue aid for up to six months.
The growing Dartmouth Flood Observatory record of major floods around the world has another practical use: identifying flood-prone areas for national flood hazard reduction programs. The flood record is also being used to grapple with a tough scientific question: Are "great floods" around the world getting larger as the Earth's climate warms?
"We have to know how big a flood event is and keep a global record of such events in order to determine if climate change is accompanied by changes in the frequency and magnitude of big floods," says Brakenridge. NASA's EOS program recently funded a multi-year research proposal by Brakenridge on this question.
For more information on the Dartmouth Flood Observatory: http://www.dartmouth.edu/artsci/geog/floods/
For more information on NASA's Earth Observing System program: http://eospso.gsfc.nasa.gov/
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