Spies and sensors everywhere

Visible light is just a tiny portion of the total electromagnetic spectrum. By measuring other spectra (or bands of light), scientists gain a wealth of information about the stuff that produces or reflects the light.

AVIRIS shows the south end of San Francisco Bay. False colors at the top show water. False colors at the sides show the edges of all 224 channels of data. Black and blue show low response in each spectrum; red shows high response. Shorter wavelength (visible) light is at the top, longer wavelength channels (showing infrared) are at the bottom. Courtesy of NASA.
  A spectrum of data
You've probably noticed that different materials reflect different kinds of light. Asphalt reflects a gloomy blackish-gray, concrete a ghastly gray, while leaves reflect green. You know these things because your eyes are sensitive to many wavelengths, or spectra, of light.

electrospectrum

As the wavelength changes, your eye sends a different signal to your brain, which tells you that you're looking at a different color. Like the eye, a multi-spectral imaging camera like AVIRIS can simultaneously measure a broad range of wavelengths (actually, far more than your eye can see). But while your eye registers the wavelengths as different colors, the spectrometer tracks them numerically. And instead of using nerve cells to detect the incoming photons, it uses electronic sensors like those found in video cameras.

Using the AVIRIS maps, the U.S. Bureau of Reclamation, Environmental Protection Agency, and Geological Survey were able to consolidate and cap the numerous waste rock piles in 1997, part of a long-term effort to control the damaging legacy of mining around Leadville.

In fact, AVIRIS worked so well that it's being used to map contaminated mining sediments in the Arkansas River valley, which drains Leadville and other former mine sites. It's also been used to track forest fires, water vapor in the atmosphere, and snow conditions. Ironically, given the use in the mine cleanup at Leadville, it can also be used to search for new mineral deposits.

Almost a trend
The spectroscopic approach seems to be catching on -- among other talents, it can find dug-in tanks or chemical weapons factories. The Air Force and an Australian organization are both building multispectral devices. However, in August, 1997, a 384-band imager that TRW built for NASA burned up in orbit aboard the ill-fated Lewis satellite (see "Faster, Cheaper Strategy on Trial" in the bibliography).

cube illustrationAnd AVIRIS is still finding new applications, such as mapping different vegetation communities in the Santa Monica Mountains, where wildfires are an annual hazard. Dar Roberts of the University of California, Santa Barbara, said, "This information would improve our ability to assess fire risk and predict fire behavior, and perhaps could provide more effective information for planners and agencies concerned with fire prevention. We can also predict moisture content in the foliage which helps us understand how different areas will burn."

AVIRIS could have another benefit for the fire-plagued region -- examining rooftops in Los Angeles, says Robert Green, the AVIRIS experiment scientist at the Jet Propulsion Laboratory. The camera can easily distinguish fireproof clay tiles from flammable roofing, he points out. Indeed he suggests that the spectroscopic approach can be useful, "Anywhere somebody wants to know the surface molecules and concentration."

But can this stuff help find my lost kid?


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