A baseline thermal infrared survey of ground heating around the Casa Diablo geothermal plant, Mammoth Lakes, CA

In October 2016, an airborne thermal infrared (TIR) survey was conducted over the area surrounding the Casa Diablo geothermal power plant, near Mammoth Lakes, CA. This data collection campaign was part of an ongoing monitoring program to assess the potential impacts of geothermal energy production on the natural surface expression of the geothermal system. The purpose of the TIR survey was to characterize and map existing thermal ground in the study area, establishing a baseline against which any future changes may be compared. The high spatial resolution (≤ 1-m pixel) imagery covers existing and proposed well fields, known geothermal areas, and part of the town of Mammoth Lakes. The TIR data were acquired at night, under clear skies and with snow-free ground, using a nadir-looking FLIR SC6000 sensor installed on a fixed-wing airplane, flown at an altitude of 1800 m above ground level. More than 3,400 overlapping image frames were acquired covering the 51-km ² study area. Raw data values were converted to radiometric temperatures based on the radiometric calibration of the TIR sensor and compared to in situ surface temperature data collected concurrently within the study area. A temperature orthomosaic was created using Photoscan Pro image processing software. Nine distinct thermal areas (including two previously unstudied sites) were mapped and characterized with the nighttime TIR imagery. Radiant background surface temperatures were below freezing at the time of the data collection. Pixel temperatures in the thermal areas ranged from 25 to 77 °C above the average temperature of ground surface. Estimates of the geothermal radiant emittance of the thermal areas ranged from 10 to 72 W/m ² ; and estimates of the geothermal radiative power output summed for all the thermal areas ranged from 3 to 8 MW. This work shows the utility of high-resolution airborne TIR surveys for geothermal site characterization and establishes a workflow for data processing that could be automated in the future.