ENVIRONMENTAL MAPPING WITH IMAGING SPECTROSCOPY OF THE WORLD TRADE CENTER AREA AFTER THE SEPTEMBER 11, 2001 ATTACK

The Airborne Visible / Infrared Imaging Spectrometer (AVIRIS), a hyperspectral remote sensing instrument, was flown by JPL/NASA over the World Trade Center (WTC) area on September 16, 18, 22, and 23, 2001. A 2-person USGS crew collected samples of dusts and airfall debris from more than 35 localities within a 1-km radius of the World trade Center site on the evenings of September 17 and 18, 2001. The AVIRIS data and ground information were used to calibrate, provide ground truth, and map the debris and its composition in the lower Manhattan area. The AVIRIS data has 2x4-meter pixel spacing. Laboratory analyses and the AVIRIS mapping results indicate the dusts are variable in composition, both on a fine scale within individual samples and on a coarser spatial scale based on direction and distance from the WTC. Replicate mineralogical and chemical analyses of material from the same sample reveal variability that presumably is due to the heterogeneous mixture of different materials comprising the dusts. The spatial variability is observed at large scales of tens of meters to centimeter and smaller scales. AVIRIS mapping suggests that materials with higher iron content settled to the south-southeast of building 2. Chrysotile may occur primarily (but not exclusively) in a discontinuous pattern radially in west, north, and easterly directions perhaps at distances greater than 3/4 kilometer from ground zero. Although only trace levels of chrysotile asbestos have been detected in the dust and airfall samples studied to date, up to 20 volume % chrysotile was found in samples of material coating steel beams in the WTC debris. The AVIRIS mineral maps may also indicate that asbestos can be found in localized concentrations. AVIRIS data were also used to show locations, areas, and temperatures of hot spots (several greater than 800 Kelvin), penetrating through the heavy smoke. The smoke prevented direct detection of the fires using visible wavelengths. See http://speclab.cr.usgs.gov for more information.