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| OFR 01-0429: World Trade Center USGS Organic Components Map |
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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 CH Figure 1a. Organic materials absorption map. |
 Larger 519 KB image CH Figure 1b. Organic materials absorption map, same as at right, but zoomed in to lower Manhattan. |
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.
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For further information, contact:
Dr. Roger N. Clark
rclark@usgs.gov
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