AVIRIS

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Airborne Visible/Infrared Imaging Spectrometer

AVIRIS measures the upwelling spectral radiance from 370 to 2500 nm at nominally 10 nm sampling. (2001Green_co2_web.pdf)

Acquisition Mode: Whiskbroom Scanner (ltid.inpe.br)

Swath Width: 614 pixels

Radiometeric Resolution: 14bit (csc.noaa.gov)


AVIRIS Data

AVIRIS Links

AVIRIS Instrument Overview

Timeline of AVIRIS at the World Trade Center Disaster Site

AVIRIS Related Published Papers

World Trade Center Hot Spots


On Sept. 16, around noon when the sun was highest, lighting as much of the dark canyons between the buildings as possible, the first of the USGS missions was flown. The first pass was at 6,500 feet above Manhattan; the second pass at an altitude of 12,500 feet. The data tapes were loaded on a FEMA jet and flown to the Jet Propulsion Lab at Pasadena. They arrived at 2 a.m., where Green and Frank Loiza were waiting. The first evaluation of the data on Sept. 17 cut through the heavy smoke and clearly showed 34 fires burning deep in the bowels of the collapsed World Trade Center complex. That was more than anyone had anticipated. Maps were prepared and shipped to emergency response teams in New York. Based on this information, firefighters redeployed their equipment and changed how they were attacking the fires, which AVIRIS measured at heat ranging between 800 degrees and 1,000 degrees. "Everything we were finding went through the White House first," Clark said. The White House science office asked that AVIRIS be flown again because more information was needed, Green said. On Sept. 18, 22 and 23, the Twin Otter and its 5 million-plus sensor crisscrossed Manhattan.

http://www.stltoday.com/stltoday/news/special/asbestos.nsf/0/8DC49C62C3BDFD2186256CAD0076A1ED?OpenDocument


Because AVIRIS measures reflected sunlight, it generally cannot detect materials deeper than can be seen with the human eye. For most solid materials this optical penetration is measured in millimeters. [ACS 919 (source ACS 919 p68)]


Dust, probably more than a few millimeters thick (the optical depth), appears in shades of brown around the core WTC area on the 16th. [ACS 919 (source ACS 919 p69)]


Beginning with the first images released on September 17, AVIRIS data showed hot spots that were otherwise difficult to detect through the smoke and debris.

(source)


Orthophotos, vector maps, and thermal data were overlaid to show the location and surface temperatures of underground fires. (source)


Another national program involved collections using NASA’s Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) instrument, which is flown aboard a de Havilland Twin Otter aircraft.7 The AVIRIS collects data in 224 channels of wavelengths (0.37 to 2.5 micrometers) in the visible to short-wavelength infrared portion of the spectrum. This instrument was flown over Ground Zero at the request of the Environmental Protection Agency (EPA) through the U.S. Geological Survey (USGS). Two flights were undertaken over lower Manhattan at mid-day, one on September 16th and the other on September 23 rd. These images provided a useful pair for identifying and comparing significant thermal hot spots at Ground Zero, which apparently had substantially diminished by the 23rd. The Jet Propulsion Laboratory (JPL) calibrated the imagery and made corrections for aircraft movements, while the USGS’s Imaging Spectroscopy Group made atmospheric and ground calibrations for the resulting image maps. The imagery data also helped in identifying and locating potential asbestos fallout from the WTC plume. (source)


AVIRIS_image_cube_9-16-01.jpg


AVIRIS image cube of World Trade Center disaster site acquired on the 16th of September 2001. The sides of the cube are slices showing the edges of the top in all 224 of the AVIRIS spectral channels. The tops of the sides are in the visible part of the spectrum (wavelength of 400 nanometers), and the bottoms are in the infrared (2,500 nanometers). The sides are pseudo-color, ranging from black and blue (low response) to red (high response). The sides depict the spectral response of the single row of pixels at the top of each side, the bands on the sides are due to the solar absorption windows. The sides of this image convey little additional information since they are not showing the spectral response of the hot spots. The full dataset is necessary. Image Cube Description ftp://popo.jpl.nasa.gov/pub/docs/workshops/02_docs/2002_Green_wtc_web.pdf


AVIRIS_09-16-01-thermalMapGeo.jpg


earthdata_c-projectssubcat_34.jpg

From http://www.earthdata.com/projectssubcat.php?subcat=34


img14.jpg


hotspot.C.900to1000.perc.gif


Remote Sensing Overview

AVIRIS data taken on the 16th was released in 2 days, AVIRIS data taken on the 23rd was released in 19 days. http://pubs.usgs.gov/of/2001/ofr-01-0405/ofr-01-0405.html

However, Clark doesn't know how deep into the pile AVIRIS could see. The infrared data certainly revealed surface temperatures, yet the smoldering piles below the surface may have remained at much higher temperatures.

Chemican and Engineering News 2003-10-20 - CENEAR 81 42 pp. 26-30 Volume 81, Number 42 - CHEMICAL ANALYSIS OF A DISASTER Scientists struggle to understand the complex mixture of aerosols released during and after the destruction of the World Trade Center (link)

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