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DISCOVERY FILE ...............................................

What do the colors mean?

Landsat was the first satellite program designed to gather multi-spectral images covering the globe. The goal was to monitor the world's resources and environments. Data from Landsat and other satellite-based sensors arrive on Earth in digital form. 00110101 11011100 01001010 00010101 11010101 01110101 01010101 But zeros and ones are hard to interpret, so they are converted into images by computers. If each pixel is assigned a shade of gray, the zeros and ones become images that resemble black-and-white photographs. Although a black-and-white image makes digital data more understandable, the number of different gray tones that the human eye can separate is very limited. We can see only about 20-30 steps when there are really 200 steps on a contrast scale. On the other hand, since our eyes can separate 20,000 or more different color tints, false color images are much better at showing the real variation in the original data. Image-processing software is used to "assign" colors. Note: there is more than one way that people can assign colors. This Landsat image shows the Old Faithful area of Yellowstone National Park, about one year after the fires. This image was acquired by the Thematic Mapper (TM) scanner. For example, in the Landsat image of Yellowstone National Park above, an image-analysis computer was used to assign the color "red" to band-7 data, and "green" to band-4 data. Band 3 data are shown in blue. Since trees and other healthy vegetation are highly reflective in the near infrared (band 4) they appear green. The newly burned areas are highly reflective in the far infrared (band 7) and appear bright red. Pale blue represents geyser basins (band 3). The yellow ribbon was added to show the location of the main park road.   For additional information about remote sensing, explore these excellent sites: http://observe.ivv.nasa.gov/nasa/exhibits/learning/learning_0.html http://observe.ivv.nasa.gov/nasa/education/reference/main.html http://hawaii.ivv.nasa.gov/space/hawaii/vfts/oahu/rem_sens_ex/rsex.spectral.1.html