PE&RS October 2002

Direct Georeferencing

NOAA's Role in Mapping the World Trade Center and the Pentagon Disaster Sites

The National Oceanic and Atmospheric Administration's (NOAA) role in mapping the World Trade Center (WTC) and the Pentagon disaster sites - to support recovery efforts - changed quickly from one of support to one of direct operational capability. The smoke from the burning Pentagon could be seen from our headquarters in Silver Spring, Maryland for several days after the attacks, and frustrated personnel desiring to help in some way or another.

On the morning of September 14, 2001 the telephones began ringing at NOAA's Silver Spring office and didn't stop. The first call was from Earthdata International requesting NOAA's National Geodetic Survey for support in establishing and occupying GPS base stations to support lidar and digital imagery surveys of the WTC site (See PE&RS, September 2002, pp 877-879). Additionally, Earthdata requested the National Geodetic Survey establish a calibration site to support lidar system calibration requirements and the boresighting of the Applanix POS AV system, which has been integrated into their digital camera. As the NOAA team was preparing to leave for New York, we received another telephone call from the U.S. Army's Joint Precision Strike Demonstration (JPSD) requesting field and aircraft support from the National Geodetic Survey. JPSD had been tasked by the Deputy Under Secretary of Defense for Advanced Concepts and Systems to support the WTC and Pentagon recovery efforts with their high-resolution terrain mapping capabilities, but unfortunately the JPSD assets were deployed out of the country. To support JPSD tasking, they assembled a team from NOAA with geodetic and remote sensing capabilities, Optech International who supplied a 33khz Airborne Laser Terrain Mapping System (ALTM) and an Intelligent Laser Ranging Imaging System (ILRIS) terrain lidar as well as personnel for operations and processing, and the technical expertise of the University of Florida Geoscience and Remote Sensing Department. The stated objective was to provide lidar post spacing of 1 meter and metric quality color negative imagery to be acquired in tandem and train and assist the users in exploiting the data.

Earthdata was to begin their remote sensing operations at 9:00 am September 14, 2001 and would need two base stations to be operational as well as the calibration data by that evening. New Jersey's Liberty State Park directly across from the WTC, less than two kilometers away, was selected for the calibration range and GPS base stations. By 8:00 pm on the evening of September 14th the NGS field crew established and occupied three base stations and collected, processed, and uploaded 12,000 kinematic GPS points and six photogrammetrically identifiable points to the Earthdata operations center in Albany, New York. In addition, NGS in, cooperation with the New Jersey Institute of Technology, supplemented the field party's efforts by turning the NGS/NJIT CORS site NJIT to 1 second to serve as a backup and as needed primary base station for the remote sensing efforts. For the next week, the NGS team continued to collect, process, and upload GPS base station data and in addition to another 30 photogrammetrically identifiable points in and around the WTC site for calibration and independent check purposes. While working at "ground zero" the NGS and Optech team were able to further support the recovery efforts by establishing horizontal and vertical control for the New York Department of Design and Construction, the agency coordinating the debris removal, and also providing valuable ILRIS terrain lidar data for the entire site.

The NOAA Citation flight crew collected two individual datasets at the WTC site on September 23 and 28 respectively. The Pentagon flights occurred on September 26 and fieldwork was accomplished two days beforehand and met the same requirements of the WTC surveys. The merged datasets of the airborne and ground based lidar systems proved to be invaluable to the recovery efforts serving several purposes including mapping and visualization products, estimating debris volumes, determining crane reach requirements, determining structural hazards through monitoring, and change detection.

Direct georeferencing played a critical role, with all the sensors and technologies that acquired remotely sensed data to support the recovery efforts. To date, the calibrations and ground truthing data that was collected by NGS has been used to validate and support operations providing lidar, digital imagery, film imagery, multispectral, hyperspectral, and data from several commercial multispectral and electro optical satellite systems.

Mike Aslaksen, Staff Cartographer, Remote Sensing Div., NOAA/NGS
John Bailey, Chief of Remote Sensing Division, NOAA/NGS
Edited by Mohamed M.R. Mostafa, Applanix Corporation

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