Maps of dust and debris show asymmetric distribution of materials.

The map images on this page (Dust Figures 1a, 1b, 2a, 2b) show locations of materials with spectral shapes similar to the spectra of field samples of dust and debris collected around the lower Manhattan area. These materials/minerals include common building materials; therefore, the maps may include materials in buildings not associated with the World Trade Center (WTC) collapse. While the minerals mapped in any one location may or may not be associated with the WTC event, a pattern is seen that appears to show the distribution of materials related to the WTC collapse. Further, the debris map qualitatively agrees with on scene observations 2 days after the imaging spectroscopy data were acquired. Production of a dust/debris map was challenging because building materials are similar all over the city (e.g. concrete occurs in many locations). However, the pulverized dust/debris does have some general spectral characteristics that can be used.

Spectra of the field samples shows a general range of spectral characteristics (Dust Figure 3). Samples WTC01-37B and WTC01-37Am are concrete that display ferrous iron absorptions (most likely due to the aggregate). The spectrum of concrete minus the aggregate is shown in sample WTC01-37A: the cement shows less ferrous absorption. Pervasive in the spectra of the debris is gypsum, and with the variations in abundance of other components, spectra of the dust and debris show the spectral variations seen in Dust Figure 3. We mapped for these general spectral shapes over the spectral range 0.5 to 2.4 microns. The ultraviolet was not included because scattering from smoke affects shorter wavelengths to much. The strategy proved effective. The maps should not be interpreted as indicating that these specific materials were mapped, only that the spectral shape is similar. However, red and yellow colors indicate areas showing more ferrous-like absorptions, and this is apparent in the WTC core zone where many steel girders dominate. Green copper roofs have a similar absorption to ferrous minerals, so they would map as red or yellow.

Two versions of the dust/debris map are shown (Dust Figure 1a, 1b, 2a and 2b). Dust Figure 2a, b is the same as Dust Figure 1a, b but without the grey-scale image background. Dust Figure 2a, b allows one to see the mapped materials without the apparent clutter of the grey-scale image.

The plume map in Dust Figures 1 and 2 indicate an asymmetry in the dust/debris distribution, with more iron bearing materials to the south by southeast. It is difficult to locate the outer boundary of the dust/debris because of the problem of matching common materials throughout the city.

The reference spectra used for matching the dust/debris was:
wtc01-37B (Note the strong Fe²⁺ absorption near 1-um.)
wtc01-37Am
wtc01-37A
wtc01-15
wtc01-28
wtc01-36

Larger 1927 KB image	Larger 682 KB image
Dust Figure 1a. Dust/Debris plume map.	Dust Figure 1b. Dust/Debris plume map, same as at right, but zoomed in to lower Manhattan.

Larger 1206 KB image	Larger 439 KB image
Dust Figure 2a. Dust/Debris plume map without the image background so the mapped materials are easier to see.	Dust Figure 2b. Dust/Debris plume map, same as at right, but zoomed in to lower Manhattan.

Larger 22 KB image

Dust Figure 3. Reference spectral shapes used for making the dust/debris map. The colors match the colors on the maps in Dust Figures 2, 3.

Images of the World Trade Center site show patterns of materials with spectral absorptions indicating the presence of C-H (organic) compounds.

The map of materials containing organic compounds (Figure 1a, 1b) shows no pattern that is indicative of the distribution of debris from the WTC collapse at the detection limit of AVIRIS. Organic compounds include any material containing C-H chemical bonds (e.g. plastics, paints, gasoline, and many types of solvents).
Because there are literally thousands of organic compounds and our reference materials spectral library only contains a few samples, we do not have the capability to uniquely identify the various types of organic materials. Because the reference spectra covering the AVIRIS spectral range is sparse, it is also unknown if AVIRIS has the spectral resolution to uniquely separate some types of organic compounds. Thus the organics map here does not indicate unique compounds. But the different colors indicate different spectral classes of organics and indicate broadly similar compositions.

The majority of the organics mapped in this area are probably related to plastics and paints. Paper, wood, and vegetation are also organic, but the spectral signatures of these materials occur with other known absorptions (e.g. from lignin, cellulose, and nitrogen) and are excluded from this map. Some aged wood, however, does have spectral features that can be confused with the other organics here (e.g. due to decreased signatures of lignin, cellulose, and nitrogen), and might be included in this map.

Imaging spectroscopy has not detected more than a few percent organic material in the WTC debris. It may be possible that more organic material exists but was not spectrally observable at the surface with AVIRIS.

Absorptions due to CH occur near 2.3 microns: the same location as (OH) absorptions in serpentines and amphiboles (asbestiform minerals). This coincidence results in a higher threshold detection limit for asbestiform minerals when CH-absorptions are present in the spectrum. Fortunately, CH-compounds also have additional absorption features (e.g. those near 1.65 to 1.75 microns, Figures 2a, b, c) that make detecting such compounds possible and reducing false positive identifications of asbestiform minerals. Thus, locations on this map where CH-compounds are present also indicate locations where asbestiform minerals are indeterminate.

Larger 1460 KB image	Larger 519 KB image
CH Figure 1a. Organic materials absorption map.	CH Figure 1b. Organic materials absorption map, same as at right, but zoomed in to lower Manhattan.

Larger 18 KB image	Larger 16 KB image	Larger 12 KB image
CH Figure 2a. Example spectra of CH compounds used to map the organics in CH Figure 1. The colors of the spectra match the colors of the materials on the map.	CH Figure 2b. More spectra of CH compounds used to map the organics in CH Figure 1. The colors of the spectra match the colors of the materials on the map.	CH Figure 2c. More spectra of CH compounds used to map the organics in CH Figure 1. The colors of the spectra match the colors of the materials on the map.