Taking the Temperature of Yellowstone from Space
We all know Yellowstone is hot… but how hot? And how can we detect park- or basin-wide changes in geothermal areas (regions that let off Earth's internal heat) that may take place over months, or years? Thermal imaging with satellites has proven highly useful at erupting volcanoes, where magma emerges at very high temperatures. Geothermal areas, though appearing hot on the ground, are more difficult to study from space because their temperatures are much lower and the signal can be masked by solar heating of the ground surface during the daytime.
USGS scientist Greg Vaughan, together with colleagues from the USGS YVO and Yellowstone National Park recently studied Yellowstone's thermal areas using satellite-based thermal infrared (TIR) remote sensing data from two NASA satellites MODIS and ASTER. This research was published in the July 2012 issue of the Journal of Volcanology and Geothermal Research. MODIS data are collected frequently, but the TIR data measure surface heat over very large areas (about 1 km per pixel). Vaughan used nighttime MODIS data to establish background thermal patterns and to quantify how much temperatures would have to change to be detectable with modern spaceborne techniques. Most natural thermal changes at Yellowstone within the past decade are around the detection limits of the technique, providing hope for future monitoring during more active periods. The ASTER data cover smaller areas with greater spatial detail (about 90 meters per pixel). Vaughan was able to use ASTER to create maps showing regions where abnormal amounts of heat are released, called thermal anomalies, and also to estimate surface temperatures and other aspects of heat flow at Yellowstone.
Within the time frame of the study, the thermal areas with the highest pixel temperatures and the highest heat flow were large acid-altered regions (e.g., the Sulfur Hills near Yellowstone Lake) and areas with large, boiling hot spring pools (e.g., Grand Prismatic Spring in Midway Geyser Basin). The ASTER- based estimate for how much geothermal heat was radiating away from all of Yellowstone's thermal areas, was ~1,970 megawatts, which is comparable to measurements made with land-based techniques that take much more time to acquire than satellite measurements.
This work provides a basis for future use of satellites to measure and monitor changes in geothermal areas around the world that are well below magmatic temperatures and have proven difficult to study with satellite-based techniques. The full article is available through the Journal of Volcanology and Geothermal Research.