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In the summer of 1988,

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a complex of fires broke out in Yellowstone National Park.

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The fires actually consumed a huge amount of acreage and profoundly affected the ecology of the Park.

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And still to this day, as you can see in the images

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the imprint of the fire remains.

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The recovery is certainly going to take decades, if not centuries to actually occur.

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In these images, the healthy vegetation is dark green.

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That's the sign of tall, healthy forest.

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And what you can see, right after the fire,

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is the very obvious fire scar. That's the dark reddish-brown color.

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Landsat actually images the earth using a variety of spectral bands, in different wavelengths.

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Some of these wavelengths are not visible to the human eye,

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but are useful for assessing the composition of the land surface.

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The red wavelength, for example, is sensitive to leaf area

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because the chlorophyll in leaves tends to reflect a lot of light in the near-infrared.

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The reflectance of the fire scars tends to be dominated by the char that's left on the ground.

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The char, initially, tends to be fairly bright in the short-infrared.

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So in this case, for example, we've assigned the short-wave infrared band to the red,

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we've assigned the near-infrared band to the green,

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and we've assigned the green band to the blue.

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And that creates what we call a "false-color" image.

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It's not exactly what you're eye would see,

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but it's quite convenient because the healthy vegetation shows up as green

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and so we can, sort of, automatically interpret that.

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One thing that's interesting about the Yellowstone site

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is that it's a very hostile site for forests.

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It's high up, it has a short growing season, it's quite dry,

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and this is probably one reason why the recovery in that area has been so slow.

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It's almost an area that's not really suitable to be forest in the first place.

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and so now it's having a hard time recovering from those fires that are so severe.

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