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.

Satellite remote sensing data from numerous orbiting spacecraft have long been instrumental in studying and monitoring Yellowstone—especially the thermal areas and geyser basins that make Yellowstone National Park famous. 

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Satellites with thermal infrared instruments, such as ASTER and Landsat 8/9, can measure the heat emitted from thermal areas.  But with moderate spatial resolution (pixels about the size of a football field), they cannot clearly detect subtle spatial changes, small thermal areas, or thermal water bodies.  High-resolution commercial satellite data do not have thermal infrared capabilities (yet), but with pixels smaller than a table (less than 1 meter, or 3 feet, on a side), they enable detection of small visible features that are characteristic of thermal areas, such as mineral deposits, vegetation stress, water discoloration and levels, snow-free zones, and persistent open water on frozen lakes during the winter.  As such, high-resolution commercial satellite data are important for accurately mapping the extent of thermal areas and detecting unique features and changes that are too subtle to be detected with moderate-resolution satellite data.

We’ve said it before, and we’ll say it again: Yellowstone’s thermal areas change a lot.  Sometimes the changes are large enough to be noticed by satellite thermal infrared sensors, for example, when a newly emerging thermal area was discovered in Yellowstone’s backcountry near Tern Lake in 2018.  But even in this case, high-resolution data from airborne and commercial satellite sensors were required to characterize the location, extent, and birthdate of this new thermal area, and to support field work in the area.  

But sometimes the changes are too subtle to be detected by the moderate-resolution images.  For example, there is a small group of hot spring pools located near a backcountry trail along the Ferris Fork of the Bechler River in the Three River Junction thermal area in the southwest region of Yellowstone National Park.  This feature cooled off and dried up sometime between August 2019 and April 2020.  At the same time, a thermal feature across the river, next to the trail, heated up and started steaming more.  Sometime during 2021 these features returned to their prior, normal states.  A combination of field photos by backcountry rangers and archived high-resolution airborne and commercial satellite remote sensing data were used to document the approximate timing of these changes.  However, with few, sparse observations, it was not possible to determine if the changes occurred at the same time as other events, like earthquakes, storms, or seasonal variations.  This local thermal disturbance appears to be a unique event over the last 20 years and remains unexplained. 

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But YVO scientists are about to get a boost in their work with high-resolution satellite data thanks to a grant from NASA’s Commercial SmallSat Data Scientific Analysis Program!  The newly funded project will enable access to satellite data from Maxar Technologies (formerly called DigitalGlobe) and Planet Labs PBC (also called Planet).  The work aims to assess and update current maps of Yellowstone’s thermal areas and thermal water bodies, and also to characterize any surface changes over time. 

Maxar’s satellite assets include WorldView-1, -2, -3, and GeoEye-1, which are capable of sub-meter (less than 3 feet) pixel imaging.  Planet’s satellite assets include 21 SkySat satellites, which can also collect sub-meter pixel images and high-definition video, plus a constellation of more than 130 CubeSats (small satellites, about the size of a shoebox).  The CubeSats provide imagery with 3–5 meter (10–16 feet) pixels and acquire new images approximately every day! 

The use of images with high spatial resolution and acquisition frequency from these commercial satellites will enable the recognition of thermal areas that are much smaller than can be resolved by moderate resolution sensors yet have a significant impact on our understanding of Yellowstone’s dynamic heat emissions and potential hazards.  

YVO scientists have already noticed interesting changes in some thermal areas using these commercial satellite data sets.  For example, previously unmapped thermal areas were recognized on the north side of Mallard Lake dome by identifying snow-free zones in wintertime images; previously unknown thermal features were discovered in and around some lakes by identifying open water on frozen lakes in wintertime (which could help with the Yellowstone’s Hydrothermal Inventory Project); and changes in thermal input at Nuphar Lake in Norris Geyser Basin were documented.  Now, YVO is set up to do even more work with these high-resolution commercial satellite data!  We look forward to sharing some of the insights from the project soon.