In the summer of 1988, a complex of fires broke out in Yellowstone National Park. The fires actually consumed a huge amount of acreage and profoundly affected the ecology of the Park. And still to this day, as you can see in the images the imprint of the fire remains. The recovery is certainly going to take decades, if not centuries to actually occur. In these images, the healthy vegetation is dark green. That's the sign of tall, healthy forest. And what you can see, right after the fire, is the very obvious fire scar. That's the dark reddish-brown color. Landsat actually images the earth using a variety of spectral bands, in different wavelengths. Some of these wavelengths are not visible to the human eye, but are useful for assessing the composition of the land surface. The red wavelength, for example, is sensitive to leaf area because the chlorophyll in leaves tends to reflect a lot of light in the near-infrared. The reflectance of the fire scars tends to be dominated by the char that's left on the ground. The char, initially, tends to be fairly bright in the short-infrared. So in this case, for example, we've assigned the short-wave infrared band to the red, we've assigned the near-infrared band to the green, and we've assigned the green band to the blue. And that creates what we call a "false-color" image. It's not exactly what you're eye would see, but it's quite convenient because the healthy vegetation shows up as green and so we can, sort of, automatically interpret that. One thing that's interesting about the Yellowstone site is that it's a very hostile site for forests. It's high up, it has a short growing season, it's quite dry, and this is probably one reason why the recovery in that area has been so slow. It's almost an area that's not really suitable to be forest in the first place. and so now it's having a hard time recovering from those fires that are so severe.