Taking Yellowstone's Temperature From Space

Yellowstone’s thermal areas mapped from satellite data. The park boundary is in red, large lakes in blue and major roads in black; the panels at left zoom in on three areas. U.S. Geological Survey.

Everyone knows Yellowstone is hot — but how hot? And how could anyone spot changes in its geothermal areas, the places where the Earth's internal heat escapes, across the whole park and over months or years?

A hard target

Satellites that sense thermal infrared light have proved very useful at erupting volcanoes, where magma reaches the surface at very high temperatures. Geothermal ground is much harder: it is far cooler, and by day its heat is masked by the Sun warming the ground.

In a study published in July 2012 in the Journal of Volcanology and Geothermal Research, USGS scientist Greg Vaughan, with colleagues from the Yellowstone Volcano Observatory and Yellowstone National Park, tackled the problem with thermal infrared data from two NASA satellite instruments:

• MODIS, which observes often but sees heat only over large areas, about 1 km per pixel. Using night-time MODIS data, Vaughan established Yellowstone's background heat patterns and worked out how big a temperature change would have to be to show up from space. Most natural changes in the park over the previous decade were close to that limit — which suggests the method could catch a more active period.
• ASTER, which covers smaller areas in much more detail, about 90 metres per pixel. With it, Vaughan mapped thermal anomalies, places releasing unusual amounts of heat, and estimated surface temperatures and heat flow.

Pixel temperature, radiant emittance and geothermal heat flux for selected thermal areas. U.S. Geological Survey.

What they found

The hottest pixels and the greatest heat flow came from large acid-altered areas, such as the Sulfur Hills near Yellowstone Lake, and from areas with big boiling hot-spring pools, such as Grand Prismatic Spring in Midway Geyser Basin.

From ASTER, the total heat radiating from all of Yellowstone's thermal areas came to about 1,970 megawatts — close to measurements made on the ground, which take far longer to gather.

The work lays a foundation for using satellites to measure and monitor geothermal areas around the world, whose temperatures, well below those of magma, have made them difficult to study from space.

Sources

• U.S. Geological Survey, Yellowstone Volcano Observatory, "Taking the Temperature of Yellowstone from Space (2012)"; rewritten in hubnx's own words. Figures from the USGS.