Laboratory and field spectrometers have proved the value of obtaining a "continuous" spectral curve covering extended segments of the EM spectrum. But for most of the early remote sensing era, technology prevented using spectrometers on moving platforms - aircraft, and certainly not spacecraft. All that changed by the mid-80s when Charge-Coupled Devices and very fast signal readout systems developed to a level where spectrometric instruments flying above the Earth could contain enough channels, each of narrow bandwidth, that could be rapidly sampled and reset so as to function as a working spectrometer. This has opened up a truly powerful new approach to remote sensing, called hyperspectral spectrometery, which already has proven to be a superior identifier of materials found at the Earth’s surface - rock types, minerals, plant species, etc. can often be identified specifically. The first truly successful model, AVIRIS, flew on aircraft. Its end products were both spectral signature plots, that closely resembled those produced on the ground, and a large number of images made from any of the plus 200 individual channels (detectors) comprising the system. Each such product was valid for the small "piece of real estate" (the pixel) examined at any moment; the resulting array leads to images of a much larger area.

Beginning in the 1980s, Dr. Alexander F.H. Goetz and his colleagues at the Jet Propulsion Laboratory began a revolution in remote sensing by developing a powerful new instrument called AVIRIS (for Airborne Visible-Infra Red Imaging Spectrometer).^* This instrument took advantage of new detector technology to extend ground-based spectrometers into the air on moving platforms. Thus, the distinct value of obtaining hyperspectral curves has made it possible to acquire detailed data on the materials and classes present on the Earth's (or other planets) surfaces. Essentially these curves are continuous spectral plots that measure reflectances from the ground, water, or the atmosphere in the wavelength region responding to solar illumination (Visible-NearIR-Shortwave IR). The plots also record the fine-details of absorption phenomena.

With these hyperspectral curves, we can now do rigorous analysis of surface compositions over large areas. Moreover, we can display the data either as spectral curves with detail similar to those on the preceding page, or as images similar to those obtained by Landsat, SPOT, etc. With spectral curves we capture the valuable information associated with diagnostic absorption troughs, and with images we get relatively pure scenes, colorized (through color compositing) from intervals that represent limited color ranges in the visible or in false color for the near-IR (NIR).We construct the images from variations in reflectance, covering very narrow bands (e.g., 0.01 micrometers). Because images can be created for each narrow band, hyperspectral spectroscopy is also referred to as imaging spectroscopy As an example, consider this pastoral scene produced as a true color image from data obtained by another imaging spectrometer (AVIRISwiss'91).