A view from above

Remote sensing technology, which uses aircraft to gather data from the terrain below, landed a starring role in the recovery efforts following the Sept. 11 terrorist attacks.

The technology's success in reading conditions at "ground zero" in New York City got scientists brainstorming ways to use sensors to deal with disasters. Consequently, advancements in remote sensing — with potential applications for the federal government — are being made.

"It was a budding technology," said Sean Ahearn, geography professor and director of the Center for the Analysis and Research of Spatial Information at Hunter College in New York City. "People on the inside realized it had a lot of potential, but it hadn't gotten exposure."

The big break came on Sept. 14 when the New York State Office for Technology asked EarthData, an aerial remote sensing firm, to conduct flights over the wreckage. State officials needed information about the site to facilitate the search for survivors and prevent further injuries.

EarthData flew its first missions the next day, taking digital photos and deploying thermal and light detection and ranging (LIDAR) sensors, which derive data from physical conditions.

The thermal sensors measured the difference in temperature between the pile of wreckage and the air, indicating potential hot spots where fire was a threat.

The LIDAR sensors bounced light beams off the debris pile to calculate its height at different points, creating 3-D models. Emergency workers compared the daily data to detect movement and identify where stability might be compromised.

A digital camera recorded images of the site and pinpointed building footprints. The locations of danger points under the wreckage — including gas, telephone and electric lines — were marked by overlaying the photos with pre-Sept. 11 maps of Manhattan.

To ensure the best results, EarthData flew the LIDAR sensors at various times during the day and worked around the sun's schedule for the other technology, flying the thermal sensors at 7 a.m. before the rubble warmed and using the digital camera at noon, when the sun cast the shortest shadows.

Although the Office for Technology served as the main contact for Earth.Data, much of the company's information passed through federal hands before reaching emergency workers in usable map form.

"Being able to look at an image and analyze it, that's where expertise from other agencies comes in handy," said Ron Miller, chief information officer at the Federal Emergency Management Agency.

FEMA turned to NASA for technical support. Bruce Davis, a remote sensing scientist from Stennis Space Center in Mississippi, served as a consultant.

"The need for hard-copy products at ground zero was extensive," Davis said. "They were not in the mood to make use of technology that didn't benefit them."

The information gleaned from the sensors enabled firefighters to move more efficiently through the World Trade Center wreckage and see what they had accomplished.

"They're down there in that rubble and it feels like they're doing nothing, but with the images, they could start to see these pathways they were making," said Linda Harrington Baker, EarthData's director of marketing and communications. "It certainly made them feel a lot better."

The company stopped running missions recently, as the fires abated, but officials have not stopped thinking about remote sensing. "There were a number of technologies that grew out of this situation by virtue of what we had to accomplish," Ahearn said.

Fires and smoke obscured the site for the first three days, posing a major challenge, he said. In response, NASA has begun developing filters for the sensors.

"NASA Stennis is trying to improve thermal sensors, particularly so we can improve seeing through smoke not only for terrorist [situations], but also for forest fires," Logan said.

In a series of "lessons learned" meetings since Sept. 11, calls for other improvements have come up.

"Our goal is to put together an end-to-end solution for the federal government that better meets their needs," Logan said.


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