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NOAA's Cessna "Citation" aircraft used for aerial photography missions.September 28, 2001 — NOAA's National Geodetic Survey and Aircraft Operations Center mapped the wreckage of the World Trade Center in support of recovery and cleanup efforts following the Sept. 11 terrorist attack. The data are being used to provide a very accurate geographic network. Building and utility engineers will be able to determine the location of original foundation support structures, elevator shafts, basement storage areas and building utility connections enabling them to concentrate their digging and recovery efforts in the proper location.

These images will also provide very accurate height measurements as the recovery efforts descend into the basement, to mitigate possible flooding from the surrounding rivers as well as to determine the volume of debris and the reach needed by cranes to remove it.

Click image for larger view. Credit "NOAA."
(See graphic legend below.)
NOAA's LIDAR image of ground zero of World Trade Center in New York City.

Click here for images 2 and 3.
Digital Surface Models created by the LIDAR system provide very accurate 3-dimensional positioning of the building structures and the surrounding area. The 3-D models, in this case, have helped to locate original support structures, stairwells, elevator shafts, basements, etc. When this data is merged with the high resolution aerial photography taken by NOAA's Citation aircraft, it will create a very accurate image with relative accuracy around three decimeters.
This was a partnership between NOAA, Army Joint Precision Strike Demonstration, Optech Inc. of Toronto, Canada, and the University of Florida. Optech and the University of Florida processed the data which produced the image.

On the LIDAR image above the following colors correspond
with the following elevations relative to mean sea level.

COLOR Value (meters) Value (feet)
Dark Green -9.272 to 0 -30.42 to 0
Green 0 to 30 0 to 98.43
Yellow 30 to 100 98.43 to 328.08
Magenta 100 to 150 328.08 to 492.12
Red 150 to 201.19 492.12 to 764.59

NOAA's efforts in New York began on the ground on Sept. 15th as NGS field survey personnel provided the necessary ground support and calibration expertise for the airborne imaging sensors—high resolution cameras and laser ranging devices. These airborne and ground-based systems will produce very accurate map products at ground zero and the surrounding area affected by the terrorist attack. Both private industry and
government agencies benefited from these activities.

The NOAA team used the global positioning system (GPS) to position both ground and airborne mapping sensors. GPS technology fixes the latitude, longitude and height of a point on the ground and in space within five centimeters. Additional support was provided by the NGS Continuously Operating Reference Stations (CORS) program, which used two of its nearby continuously operating GPS sites to collect data for the remote sensing missions.
Similar work was performed at the Pentagon on September 26-28.

The NOAA Citation jet, N52RF, usually used for remote sensing and high resolution photography for coastal mapping, was outfitted with an Optech LIDAR (Light Detection and Ranging). Collecting both LIDAR data and high-resolution photography, the Citation flew over a five-square kilometer area of lower Manhattan.

Flights over the World Trade Center took place Sept. 23 and Sept. 26. There were two flights lasting four hours each. The NOAA Citation jet flew at an altitude of 5,000 to 6,000 feet.

The NGS field support team included Mike Aslaksen, Ed Carlson, and Jason Woolard. The Citation crew included Lt. Cmdr. Brad Kearse, Lt. Mike Weaver, and Lt. Will O'Dell (pilots) of the NOAA Commissioned Corps and Aircraft Operations Center; and Steve Nicklas of NGS.

The U.S. Army Joint Precision Strike Demonstration initiated and coordinated the entire effort. Army JPSD worked closely with NOAA, Optech Inc. and the University of Florida to produce the images and map products.

Relevant Web Sites
NOAA's Citation Aircraft

Light Detection and Ranging (LIDAR) — with sample images

NOAA's Coastal Aerial Photography

Citation Photos: 1, 2, 3, 4, 5, 6

Media Contacts:
Greg Hernandez, NOAA, (202) 482-3091 or Jeanne Kouhestani, NOAA Office of Marine and Aviation Operations, (301) 713-3431 ext. 220