cunny matters logo

 

December 2001

An Integrated City University Responds to the WTC Crisis

Bold, High-Tech TV Magazine Invites "Study with the Best"
NYC Past in Full Array At Inaugural History Festival
CUNY Community Colleges: Vital to City Economy
Arthur Miller Drops Back In for Finley Award at CCNY Dinner
Archaeologists Research Vikings
Faculty Experts Join Collaboration on World Trade Center Future
New Research Foundation Head
Asthma Initiative at BCC Registers Major Success
Oysters Reintroduced to Bay
York Grad Makes Naval History
Managing the 9/11 Crisis at BMCC
Hunter Cartographers Prepare Vital Ground Zero Maps For Rescue
CCNY’s Rosenberg/Humphrey Interns Continue Public Service Tradition
City Tech Prof Sheds Light on Titanic
New Device for Medical Diagnonis
Mina Rees, Pioneering Military Scientist
Annual Perspectives Nears 25th Anniversary
University to HIV Children: “Toys (and Lots Else) Are Us”
 
 

Hunter College Cartographers
Aid Workers at Ground Zero


Jeffrey Bliss, Research Associate at the CARSI Center, Hunter College, reports on his experience performing vital mapping work at Ground Zero.

Illustration D
-Illustration A

We see a red light at the intersection of Second Avenue and 57th Street, but since there is no cross traffic we decide to run it. We pursue our scoff-law tendencies down Second Avenue until we are finally halted and asked for credentials at a checkpoint. I display my CUNY ID, and my passenger, Al Leidner, a high-ranking City official, flashes his. Our cargo raises questions, so we inform the sentry of our mission and explain the purpose of three computer-generated maps we have that are just minutes old. Passage is permitted.

Illustration A
-Illustration B

Several more checkpoints greet us as we head toward the World Trade Center site through a city-scape eerie in its absence of pedestrians, cabs, and almost all vehicular traffic. Fire trucks and police cruisers ply the streets like hornets circling a damaged hive. As searchlights rove the sky in search of unknown objects, we finally arrive at "The Bunker." We gain entry to the structure after rigorous inspection of our personal possessions by more armed officers.
With the events of September 11, I knew that my life was to change, but could not comprehend the extent. It was not until the next day that I learned the research laboratory I worked in at Hunter College possessed the only useable database of our city's geography and infrastructure. The City's databases maintained in its emergency preparedness office had been destroyed. It would be next to impossible to conduct any type of rescue effort without the information this digital data contained. When City officials saw the maps we delivered, they instantly recognized that such maps would be crucial to the rescue and demolition processes.

Illustration C
-Illustration C

Our lab, the Center for the Analysis and Research of Spatial Information, known as CARSI, is the brainchild of Hunter College professor of geography Dr. Sean Ahearn. He formed it in 1994 to study the differences and causes observed in measurable phenomena that exist in three-dimensional, geographically oriented space.

After being hastily enlisted in the smoky and dusty chaos of Ground Zero, Ahearn brought together his CARSI staff of graduate students, including myself, for several weeks of urgent work, analyzing data and producing cartographic representations of the landscape of disaster, some of them rolling out of a huge 54-inch-wide Hewlett Packard printer. While Ahearn never envisioned his lab would be used in this grim fashion, he and the CARSI staff are gratified to have been able to contribute to the return of Lower Manhattan to the citizens of the city. We have been particularly gratified to assist those who have heroically and unselfishly endured work in the fragile, risk-laden wreckage at Ground Zero. What follows is a brief description of the cartographic stages of our work within the CARSI lab and some of the images that were used at the site of the World Trade Center disaster.

Illustration B
-Illustration D

Our first cartographic product was a hard-copy detail focusing on the WTC prior to the attack (illus. B). This detail was taken from a spectacularly large digital aerial ortho- photograph of all five boroughs that was captured in 1996. (An orthophoto has had the distorting effects of the earth±s curvature removed.) This orthophoto was assembled from 1,800 individual photos, gained through fly-overs, into a single, seamless whole 130 feet tall by 125 feet wide. Needless to say, the entire image exists only in digital form, at least until we commission the flamboyant conceptual artist Christo to use it on one of his famous drapes.

This single large image had been produced as the result of a mathematical process in which individual sectors were brought together. A Global Positioning System receiver was employed as each image was captured, producing a quite impressive level of precision.

Since Manhattan from 14th Street to Battery Park in our monster photo would require a sheet of paper 16 feet by 14 feet, we decide to reduce to half scale. Prior to printout, we labeled features for easy reference—including overlays of infrastructure, building footprints, and subway entrances; these large maps were used by the Office of Emergency Management (OEM) for planning. Smaller area-specific "scrolls" were printed and distributed to rescue/demolition workers. It was soon deemed necessary to create post-collapse geo-referenced photos, and over- flights commenced on September 13th. We processed and enhanced these preliminary images, printed them out, and delivered them to OEM.

Illustration E
-Illustration E

Smoke rising from the debris foiled the first over-flown images, and so a new technology was suggested: LIDAR or Light Detection and Ranging. In addition to "seeing through smoke," this would also provide an assessment of the cubic size of the debris field, since the output of a LIDAR sensor is the elevation of objects. This is because its laser beam operates at a wavelength not attenuated by smoke. LIDAR first sends a light beam to earth from an aircraft, then calculates the time it takes for the reflected beam to return to the aircraft. Distance is then computed and converted to height above sea level every 5 feet in all directions of the selected area.

Advances in Geographic Information Science (GIS) software and high-speed computers give geographers tools to manipulate LIDAR's drab data (just gray dots on a black background) and transform it into striking color presentations. Seen here (illus. D) is a color image created by converting the point data into a solid surface and assigning color to elevation ranges. Areas of orange are below street level, street level elevations uses brown hues, and greens to blues represent height above street level. This data set gave the first clear rendering of the extent of damage. This data set was then converted into a 3D image that could be viewed from all angles.

Shown here (illus. C) is such a 3D image looking south. WTC Building #7 is the seen as the round heap at low center. Just below it between two streets, is BMCC's damaged Fiterman Hall. Areas of orange are below street level. This data set was further manipulated by conversion to a 3D image that could be viewed from all angles.

Digital data is so much more protean than its hard-copy counterpart! Once LIDAR data was converted into 3D, other novel possibilities became apparent. For example, we sliced the data model in half and then viewed it from the side (illus. A), enabling us to view Ground Zero in slices, much as Magnetic Resonance Imaging (MRI) allows doctors to explore internal organs in cross-section.

LIDAR data from July 2000 was also compared with post-collapse data, allowing changes in elevation to be discerned. Two post-attack LIDAR data sets can be used similarly to quantify debris removal, settling, and subsidence of the ground where damage to underground structures might cause a further collapse.
A growing concern over heat rising to the surface of the debris became an issue, since areas of high heat could cause a softening of materials and further collapse. CARSI was able to supply images showing thermal flow (illus. E, with old WTC footprints underlaid) through overflights with a thermal sensor. This data was enhanced to show the hotspots and ignore all else. New data was obtained daily, and a progression of this heat was then mapped out.

CARSI continues to provide support to Ground Zero in all manner of spatial analysis. The destruction of New York±s tallest buildings gave rise to unconventional and extemporaneous techniques in data interpretation. Though the challenge was daunting in its scale and sense of urgency, we came away with some successes. Some of our experiments didn±t work, but that is where it is good to be a graduate student. Given Dr. Ahearn±s insight, we plan to re-examine our efforts and solve some of the geographical riddles exposed by the shattering events of September.

CARSI researchers will also be returning to work on a variety of globe-spanning fronts. Asia, for example, is the venue for tiger preservation research in Nepal and in Thailand, and the New York metropolitan area is the site of CARSI study of West Nile Virus dispersion. There are currently two mapping projects, one in Puerto Rico, the other in Nepal. Our largest work, however, is the NYCMAP project for the City of New York. This cutting-edge enterprise will change the way New York—and all cities—manage infrastructure, since all city agencies will employ the same database and map to conduct daily operations. The database will be maintained and updated in such a a fashion that changes made by one agency will be seen by all other agencies.

And it was the NYCMAP project, after all, that provided us with the database to support to the World Trade Center relief effort. With the OEM back on its feet, more and more of our attention is now being devoted to a tragic new CARSI speciality: the spatial analysis of disaster. There is much more to learn.

All images courtesy of the CARSI laboratory.