"I hope someone can help," someone using the name ZuluOne wrote to an online bulletin board. "I am trying to get a current overlay for the area around 2203 Curcor Court in Gulfport, Miss."
Sprague knew that "current overlay" meant a bird's-eye view. And an altruistic impulse combined with an urge to play with a new technology propelled him into action. Using his PC, he superimposed a freshly available posthurricane aerial photograph over a prehurricane image of the same neighborhood. After 15 minutes, he had an answer.
"Actually, it looks like your house looks pretty good," Sprague told ZuluOne by e-mail. "Unfortunately, it doesn't look so good for some of your neighbors. Best of luck to you and your family."
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By the end of last week, a grass-roots effort had identified scores of posthurricane images, determined the geographical coordinates and visual landmarks to enable their integration into the Google Earth program, and posted them to a Google Earth bulletin board--the place ZuluOne turned for help.
Most of the images originated with the Remote Sensing Division of the National Oceanic and Atmospheric Administration, which has been posting them to its Web site since Wednesday.
Taking inspiration from the online volunteers, Google, NASA and Carnegie Mellon University had by Saturday night made the effort more formal, incorporating nearly 4,000 posthurricane images into the Google Earth database for public use.
"It was 100 percent a reaction to what they were doing," John Hanke, a general manager who is in charge of the Google Earth service, said Sunday. "They knew about the NOAA data before Google did."
The ready availability of such images to any Web user shows not only the reach of the Internet but also the strides that have been made in the photography. Mike Aslaksen, acting chief of NOAA's Remote Sensing Division, said that while it took a week to process and make public images taken of the World Trade Center after the terrorist attacks four years ago, the post-Katrina images have been available within 24 hours.
They are not satellite photos, but aerial images taken from a Cessna Citation jet. Still, they can be readily patched into the Google Earth database as overlays.
The images are not crystal clear, and if an area appears to be flooded, it is hard to tell how deep the water is. But the photographic overlays give a sense of a home, street or neighborhood's condition. "People who have a reason to be personally concerned with what's happening there are motivated to do it," Hanke said.
Yet many who have no particular personal connection to the hurricane's devastation joined the effort.
Douglas Hillman, a disc jockey and dance instructor who lives near Chicago, created some 80 overlays. He said he was fascinated by Google Earth and also interested in "the results of a natural disaster, in the way people react to it, and also in the technology used to cover it."
As for methodology, Hillman says he downloads an aerial image from the NOAA Web site to his computer, then tweaks it with tools in the Google Earth software until it lines up as closely as possible with the existing satellite image.
"This is not an entirely precise process, as the pictures are taken from slightly different angles, so it's not exact," he said. But it is close enough to pinpoint houses, even cars.
Kathryn Cramer, a science fiction editor in Pleasantville, N.Y., whose Web site has served as a clearinghouse for overlay information, said the effort started early last week when she and a few others wondered about the exact location of a levee break and created an overlay using a photo from the news media.
"We were getting a lot of decontextualized disaster photos that didn't give you a real understanding of what was happening," she said.
In a related online collaboration people are plastering a Google street map with electronic pushpins marked with information like "casino boats destroyed" and "minor wind damage." And at Google Maps, posthurricane images are also available for flooded areas of New Orleans.
Of the many lessons learned since the 2001 terrorist attacks, "one is that there is an overwhelming desire for geospatial data," said Aslaksen of NOAA. "It's become a tool as necessary as a word processor."
The intended uses of the NOAA images, of course, are official. For instance, the photos are helping the Army Corps of Engineers to assess levee damage, Aslaksen said, and NOAA has used them to determine major shoreline changes that might pose a risk, and to see if piers or vessels have sunk. The Federal Emergency Management Agency has also used the images for damage assessment.
But Aslaksen said he welcomed the popular use. "We thought it important to give the public access to the data," he said.
Aslaksen, whose e-mail address is on the NOAA Web site, said he had received nearly a thousand e-mail messages from people seeking information on the condition of their homes. He tries to respond to all of them, he said.
Cramer said she had been able to help nearly two dozen people looking for information about the status of their homes. "I've been thanked more in the last 48 hours than ever in my life," she said Friday.
When NASA, Carnegie Mellon and Google began their more formal operation, it made the impromptu efforts of people like Hillman less crucial. But they filled an important gap, like early volunteers piling sandbags into a breach until the heavy equipment arrives.
"There's not a lot that I can do to directly help, up here in Northern Illinois," Hillman said. "I'll donate what I can to Red Cross, but beyond that, I feel like this is one actually helpful thing which I can be doing."
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