Assessment of Geospatial Technology Applications by the U.S. Army Corps of Engineers during World Trade Center Operations

Report Prepared by The George Washington University
Institute for Crisis, Disaster, and Risk Management

5. General Findings

From a perspective of the typical USACE response operations, the WTC response was a small-scale disaster. Even though there was a lot of debris and many people died, a compact area of only approximately 16 acres was the focus of operations, whereas in typical cases, the USACE has to respond earthquakes, hurricanes and floods that extend beyond boundaries of several different jurisdictions covering thousands of acres. Also, unlike the typical USACE missions, the USACE played a support role during the response to WTC attacks due to the fact that NYC had the necessary resources and only required technical consulting services from the USACE. Another non-typical fact was that although it was a no-notice event, the WTC attack was not dynamic. There were no aftershocks or resultant flooding which meant that nothing changed significantly from the perspective of the USACE ESF#3 operations other than the size of the debris pile. In contrast, from an ESF#9 mission perspective, the damaged slurry wall surrounding the WTC was a major issue since its failure would mean the Hudson River entering the Manhattan Subway System and flooding the entire area. The use of GT was limited due to these unique aspects of the WTC event.

5.1. Provision and Use of Geospatial Technologies by the City of NY

When New York City’s original EOC was destroyed by the attacks on Sept. 11, 2001, many of the city GIS staff that were in close proximity to the WTC were forced from their offices and the City had to recreate an ad hoc mapping center to provide GIS capability. For the first two days, there were only two workstations and a plotter to use. By September 14, 2001, the EOC was re-established at Pier 92, a large ship terminal on Hudson River, with the assistance of FEMA and private hardware and software vendors. NYC GIS personnel obtained 20 GIS workstations and 5 plotters to create a mapping center to support all operations at Pier 92. Since the spatial data for NYC was managed at the agency level before the attacks, and the city was in the midst of developing a comprehensive enterprise GIS that was not ready for use, data had to be found and reassembled from various departments (NYC Dept. of Parks, Dept. of Finance, Dept. of Planning, Dept. of Buildings, Metropolitan Transit Authority, and the Dept. of Environmental Protection), Federal agencies (notably USGS, NASA and DoD) and private vendors (notably ESRI).  Alan Leidner, NYC GIS Director, who was interviewed by the GWU team, was responsible for bringing together a series of teams to support a 24 hour-a-day operation involving many GIS specialists from agencies throughout the City, universities (notably Hunter College Geography Department) and volunteers.  The first maps were prepared based on aerial photographs from the NY State Emergency Management Office and satellite images from Space Imaging, a commercial company.  Simple street maps of Lower Manhattan were created using aerial images along with the NYCMAP.

Example of a NYCMAP output

NYCMAP (“nice map”) was the City’s first accurate, 1:1200 scale planimetric basemap generated from digital orthophotos. The orthophotography (1-foot pixel resolution) was acquired in 1996. Efforts to re-fly the city had begun in spring 2001 to update the basemap. However, the updated imagery was not available for the WTC response operations.  NYC Dept of Planning, with the contribution of Hunter College, provided significant amounts of data for base layers including street centerlines and parcel information. For the first couple of weeks, a ‘Sneaker Net’ was set up where State Police couriers delivered imagery and data on CDs. Data was brought to Pier 92 by hand from discrete sources due to the fact that there was no network connection and due to security concerns. When data came in, the EOC placed it on an FTP site shared with New York State (NYS) and USGS.  NYC Office for Technology began uploading data to mirror FTP servers hosted by the State and by the USGS. Field data was also obtained in order to map the changed geography of Manhattan and to support response and recovery operations. These data included search and rescue grids, command post locations, utility outages, pedestrian and vehicle access zones, subway and bus line status and river crossing access. These data were fed into custom ArcView maps called “Standard Map Products” that were created to keep the public informed and would later on be posted on the NYC’s Website. The mapping center at the EOC also began processing numerous specific queries for planning and analysis from various local and Federal agencies. The most important of these included: maps identifying destroyed, heavily damaged and lightly damaged buildings, light detection and ranging (LIDAR)-based three-dimensional analysis maps of the debris field at Ground Zero, thermal image maps that helped determine the relative distance of fires to the underground storage tanks, and maps locating oil fuel tanks at the WTC.  The mapping center generated hundreds of standard mapping products that soon overwhelmed their system. Eventually, an online map request system was created which provided a prioritized queue to the mapping staff.  Also, some procedures and mechanisms to properly process, update, monitor and archive those products had to be created. A list of most useful standard mapping products, obtained from Jim McConnell, Manager of NYC OEM GIS Operations, is included in the Appendix to this document.

NYC provided the FEMA DFO, located at Pier 90, with base map data along with a continuous feed of imagery that was flown daily and every data including orthophotography, LIDAR, and thermal infrared data. FEMA chose not to directly access the City’s FTP Server due to its concerns of connecting to a ‘non-central’ network and a virus (NIMDA) that prevented the access for quite some time. FEMA then had to rebuild its own data server. The city provided data on CDs to FEMA, and in some cases, FEMA had to purchase data.  FEMA and USACE GIS personnel stated that this situation created redundant data collection and mapping, but could not specifically quantify the degree of redundancy.

5.2. Provision and Use of Geospatial Technologies by the City of NY

Example of a GT image

The direct use of GT by the ESF#3 Team on the ground at WTC was minimal. The ESF#3 USACE mission required the use of GTs  primarily for (1) Monitoring the stability of buildings and (2) quantification of debris for reduction, removal and disposal. For debris estimates, building drawings, floor plans, maps, aerial orthophotos, LIDAR and various 3D GIS models of the area surrounding the WTC were used. USACE obtained these materials through ESF#5 located on Pier 90.  NYC provided the original building design drawings and the subterranean floor plans.

Several agencies and companies collected vertical aerial photography. FEMA chose to purchase air photos and LIDAR data collected by the commercial company EarthData, in CD format, for the first couple of weeks of the operations. EarthData’s LIDAR and orthophotography were processed by the NYS Office of Technology (OFT) in upstate NY at a NASA center. OFT was the primary agency for coordinating the remote sensing collection among Federal agencies and commercial firms. Airborne LIDAR data was used to map surface elevations each day. The debris pile was monitored using multiple scenes of LIDAR since there were concerns for response personnel working on and in the piles.

The ESF#5 Team customized ESRI’s Arcview 3.2 and its extensions in order to help estimate the quantity of debris. The custom model helped take general debris polygons, representing standing or damaged structures, and determined the volumetric amount of debris that could be expected following demolition. Rather than doing ‘one-by-one’ hand calculations, they came up with the polygons to determine the amounts.  This model required the use of rectified images with sufficient resolution. Image Analyst was used for different image interpretation and to reclassify and rectify images. Unfortunately, the accuracy of the results was limited by the inaccuracy of EarthData’s LIDAR data and the turnaround time. For instance if something was 1.5 feet, it could be rounded to either 1 or 2 feet in the model input process, which would affect the results considerably. This application did provide general trends; however it was not recommended for daily evaluation of change of the debris pile but was appropriate in monitoring the weekly changes.

The ESF#5 Team also employed Transportation Network Analyst, another commercial off-the-shelf (COTS) product by ESRI, designed to depict the traffic flow, location, capacity, and functional status of roads, bridges, railways, navigable waterways and ports and to estimate the optimal routes between debris site and the landfill site. Transportation Network Analyst was used to get a rough idea of the amount of time it would take to get to and from the three loading facilities (Hamilton Marine Transfer, 59th Street Facility, and Pier 6) plus the unloading time. This information was then used during the briefings to help decision-makers, including ESF#3 Team and debris contractors, decide on the number of vehicles required to haul the debris. For the first three weeks the database to support these models was obtained within a day’s time from FEMA through NYC. Although the results were not deemed 100% accurate, they were within a reasonable range and the models served their purpose. ESF#5 members were very familiar with the application since it had been used successfully in past disasters (notably in flooding events).  As a sidebar to this issue, these models require the use of rectified images, which are positionally accurate images, or image-mosaics of sufficient resolution and timing. The sources of these rectified images are USGS digital orthophotos and commercial imagery.

The main mission of ESF#3 in support of ESF#9 members was to augment the FEMA US&R Task Forces by providing Structural Specialists (SS) to assist the US&R activities. The USACE US&R SS Team worked with FEMA US&R personnel and NYC consultants to assess “triage” repairs of peripheral damage across from the WTC. Major areas of concern were the stability of the subterranean slurry wall and shoring of the damaged buildings to mitigate “spear” falling hazards. Several inspections involved evaluating temporary rigging and shoring constructed on several floors of the American Express (“AmEx”) Building to stabilize undermined concrete flooring. Of particular concern was temporary rigging intended to anchor what became known as the “spear” – a 25-ton exterior section (lodged in the AmEx southeast corner) that was projected from one of the WTC towers.  Digital maps and some 3D models were developed to track these concerns.  The Corps US&R SS cadre obtained building floor plans and subway designs from the Port Authority in order to facilitate the search and rescue efforts.

Search Status - Cumulative Cross Section

During the first 3 weeks, there were 24 persons working in support of FEMA GT missions. FEMA supported the US&R at the Javits Convention Center by providing mapping and imagery products. Those products included a hazards map depicting the reach of cranes and debris, a mapping product identifying the searched areas, a general base-map of US&R operations facilities and a situation map of updated daily imagery. Most of these products were in paper form and a person would physically deliver the updates and staple the product to the recipient’s board. US&R team members were debriefed for data before and after every shift to help in developing and updating maps depicting the searched areas.

Collapsed Status - Cumulative B-1 Level

The USACE SS team used floor-by-floor “collapsed status maps” for their US&R missions. These maps were also prepared by the ESF#5 team and provided to the SS team. They were made from hand-sketched drawings of the limits of collapse observed below the ground level by US&R personnel, and this information was then transferred to maps that were produced and copied for subsequent iterations. They used floor plans in order to create color-coded collapsed status maps. The picture on the previous page is an example of a cross section and the picture on this page is a floor-by-floor collapsed status map. The USACE, through its GIS personnel, worked with FEMA to create Building Status Maps for Disaster Medical Assistance Teams (DMAT) since DMATs had very limited GT capability. These maps were printed on waterproof paper and contained building names, numbers, and building “status” (e.g. partially collapsed, required cleaning). The ESF#5 made photocopies of these maps to distribute to the FDNY also. The USACE SS Team Manager, Mr. Wingate, feels that this type of map products would be very helpful for similar applications, planning purposes, and earthquake response efforts. Field revisions noted by Mr. Wingate during an inspection of the Interborough Rapid Transit (IRT) “1-9” Subway constituted the last changes of the USACE WTC subterranean collapse status maps; sketches were transferred by Kevin Carlock for the last iteration of the maps on 14 October.  Mr. Wingate subsequently met with FDNY for the last time to distribute the final set of maps, during which John Norman, FDNY Battalion Chief of Special Operations, stated “FDNY could not have done it without the Corps” – referring to the structural expertise, added safety measures, and mapping products that were provided.

During the course of the operations, there were increasing concerns regarding the propagation of a large crack on the slurry wall due to excessive vibration associated with demolition and debris removal efforts. One of the major issues for the USACE response efforts was dealing with subterranean debris removal while maintaining the stability of the slurry wall. There were fears that the debris inside the slurry wall was keeping the wall from collapsing. Collapse of the slurry wall would mean the Hudson River entering the subway system and flooding the area. Removing the debris necessitated stabilization of the wall, and there was a danger of collapse in the subterranean levels due to excessive vibrations. Some of the maps indicated the location of the slurry wall, which was not visible to those working on the surface. For pulling debris out from subterranean levels, the USACE team members used CAD based and three-dimensional maps that were produced by outside consultants such as the company Brainstorm that specialized in 3D computer animated solutions, Mechanism Digital Effects, and J. A. Construction. The research team visited Brainstorm and observed some of those 3D models of the WTC site showing both above ground and the subterranean levels. Toward the end of his involvement in the response efforts, the USACE US&R SS Team Manager was invited to participate in discussions that pertained to long-term disaster mitigation strategies which included multi-floor mapping of inner-city high rises.  Three dimensional mapping ahead of disasters might help provide situational awareness for first responders as well as facilitate planning efforts.  Geospatial mapping could also provide benefits of clearly indicating proximity to relevant information such as hazardous material storage bays.  Three dimensional mapping efforts were applauded by NYC Emergency Management personnel as a means to improve future planning and disaster response strategies.

The USACE US&R Team Manager participated in meetings with Mueser Rutledge Consulting Engineers (MRCE), NY State Emergency Management Office (EMO), NYC OEM, NYC Emergency Mapping, and others regarding the integrity of the slurry wall. The USACE US&R SS also participated in slurry wall inspections. NYC met the challenge of the daunting implications associated with potential slurry wall failure through a myriad of efforts, including 24-hour monitoring; extra emphasis on keeping heavy equipment away from the wall footprint; dewatering to keep the groundwater phreatic surface away from the wall; injecting concrete plugs into the Port Authority Trans-Hudson (PATH) train tunnel; and reestablishing steel tiebacks into bedrock. The subterranean collapse status maps helped to provide situational awareness not only to US&R personnel but to engineers inspecting the slurry wall.  USACE participation in GIS mapping and meetings surrounding slurry wall issues led to increased emphasis on maintaining stability of the wall. USACE is tasked by FEMA in situations like the collapse of the WTC because they have unique engineering expertise that offers a safety buffer for US&R personnel to mitigate against post-event collapses.  Sometimes US&R team members and engineers lack training that is specific to providing and maintaining safety during urban search and rescue efforts; emergency “shoring” for example, is a component of US&R structures specialist training.  While post-event collapses characteristic of earthquake aftershocks would not be a component of terrorist attacks, the aggressive demolition effort in this case definitely prompted concern about the stability of the slurry wall – which translated into concerns about subterranean safety.  For example there was a situation where an area collapsed after rescue teams had exited.  The collapse was due to structural instability as a result of compromised basement floors.

The US&R Teams were provided access to thermal imagery and began superimposing thermal data on collapse maps in October. This thermal imagery was collected on the same over flights of the WTC as the airborne LIDAR data that was being used to map the surface elevations each day. The National Information and Mapping Agency (NIMA), located at Pier 90 produced these maps. Firefighters and other responders contended with intense heat associated with the super-heated steel for weeks; some were coming back from shifts with the bottoms of their boots melted. The proximity of elevated temperatures, collapse patterns, and delineation of the slurry wall were all important map features; all 3 layers of this information were superimposed on the same map. These thermal images were used for locating fires, whether new or continuous, within the debris pile to identify the risks and protect the response personnel.