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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.
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.
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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.
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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.
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| -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.
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| -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.
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