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  • Hyperspectral Imager Sends Answers from Above

Photonics Spectra
Feb 1997
R. Winn Hardin

In the Colorado River valley, farmers have been trying to keep crops alive with water that was apportioned by the federal government back in 1923. Unfortunately, the river reached its highest point in a century in 1923, leaving farmers with two choices for the next 99 years: find a way to determine which crops need more or less water in a given season, or ask Washington for a new allocation study. Luckily, TRW Inc. of Redondo Beach, Calif., had an answer.
Using a state-of-the-art hyperspectral imager, airplanes flew over the southern Colorado River area, recording the spectral auras of crops. The data provided farmers with information necessary to negotiate new water allocations as well as pinpoint crops in need of additional fertilizer and other key elements.
Keying on the billion-dollar remote satellite sensing industry, TRW has built a hyperspectral imager that "sees" the Earth in 384 narrow spectral bands. Previous spectral imagers could register an object's spectral signature in a few wide bands, providing limited information. The increased imaging ability not only identifies objects, but determines a variety of object data such as the chlorophyll content of vegetation, the location of mineral deposits, and disaster assessment and relief.
Using two imaging spectrometers with an optical train constructed by OptoSigma of Santa Ana, Calif., a shortwave infrared focal array from Rockwell International and a panchromatic camera, the instrument sees in the visible, near-infrared and short-wave infrared between 0.4 and 2.5 µm, resulting in hyperspectral images with 30-m spatial resolution. The 5-m panchromatic camera's black-and-white images allow further spatial sharpening of the image. A focal plane array detects the spectral fingerprint and stores the data in a solid-state recorder for later downlink to a TRW facility in Chantilly, Va.
Operating like a push broom, the hyperspectral imager gathers spectral data across 7.7 km as it passes overhead. The imager has already logged more than 300 h in various aircraft tests in preparation for the soon-to-be-launched Meriwether Lewis satellite, also built by TRW as part of NASA's Small Spacecraft Technology Initiative program.

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