Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week’s contribution is from R. Greg Vaughan, research scientist with the U.S. Geological Survey.
Thermal infrared satellite images are an important volcano monitoring tool that can be used to estimate surface temperature. And, in fact, these data are freely available for Yellowstone and many other volcanoes worldwide. But interpreting these images is not as straightforward as it might seem — what shows up as either hot or cold depends on a variety of factors.
Every object that has a temperature emits energy, or electromagnetic radiation, into its surroundings. The characteristics of this emitted radiation are primarily a function of the object’s temperature, and secondarily a function of the object’s emissivity, which is essentially a measure of how efficiently, or inefficiently, materials radiate their energy. For example, a metal roof will appear much colder in thermal infrared images than a natural rocky or soil-covered surface, even if their actual temperatures are the same.
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The electromagnetic radiation given off by an object travels at the speed of light as discreet bundles of energy called