Development and comparison of Landsat radiometric and snowpack model inversion techniques for estimating geothermal heat flux

We present the first quantitative representation of the intensity of Yellowstone National Park's surficial geothermal activity mapped continuously in space. A radiative thermal anomaly was remotely sensed throughout a 19,682-km2 landscape covering Yellowstone National Park in the northern Rocky Mountains, USA. The anomaly is the residual terrestrial emittance measured using the Landsat Enhanced Thematic Mapper after accounting for elevation and solar effects, and was hypothesized to be an estimator of a lower bound for geothermal heat flux (GHF). Continuous variations in the anomaly were measured ranging from 0 W m− 2 up to a maximum heat flux of at least 94 W m− 2 (at the 28.5 m pixel scale). An independent method was developed for measuring GHF at smaller scales, based on inversion of a snowpack simulation model, combined with field mapping of snow-free perimeters around selected geothermal features. These perimeters were assumed to be approximately isothermal, with a mean GHF estimated as the minimum heat flux required to ablate the simulated snowpack at that location on the day of field survey. The remotely sensed thermal anomaly correlated well (r = 0.82) with the snowpack-inversion measurements, and supported the hypothesis that the anomaly estimates a lower bound for GHF. These methods enable natural resource managers to identify, quantify and predict changes in heat flux over time in geothermally active areas. They also provide a quantitative basis for understanding the degree to which Yellowstone's famous wildlife herds are actually dependent on geothermal activity.