Monitoring of Geothermal Areas Using Fixed-Wing UAV-based Thermal Imaging, Reykjanesvirkjun Geothermal Area, SW Iceland

Abstract

In August 2018, a fixed-wing UAV (unmanned aerial vehicle) was flown by Svarmi ehf. at dusk over a ~2 km2 geothermal area surrounding the Reykjanesvirkjun Power plant on Reykjanes Peninsula, SW Iceland for use by HS Orka hf. geothermal company. The UAV was equipped with a FLIR ThermalCapture Fusion LWIR (long-wave infrared) sensor with 0.05 K thermal sensitivity and 640 x 512 pixel resolution. Due to the efficiency of the fixed-wing UAV, the area was mapped in a single 20-minute flight at an average GSD (ground sampling distance) of 41 cm/pixel. An absolute temperature orthomosaic (aerial image) as well as a thermal 3D pointcloud were created using photogrammetry from the resulting radiometric jpeg images. In-situ temperature loggers placed on the ground at the time of imaging indicate an accuracy of the thermal orthomosaic of +/- 1 °C. The thermal orthomosaic was georeferenced using key ground features to a high-resolution (5 cm/pixel) aerial image created with the same UAV equipped with a RGB (red-green-blue) camera. Thermal mapping of geothermal areas with fixed-wing UAVs shows high potential for cost-effective and accurate monitoring or exploration of large geothermal areas. The use of thermal photogrammetry produces both 2- and 3-dimensional datasets, whereby changes in height can be monitored in addition to surface heat expression. This time-efficient method also means that large areas can be surveyed multiple times a year, offering more spatial and temporal data for geothermal companies at lower cost than traditional ground-based mapping methods. Repeat surveys will be conducted by Svarmi ehf. annually to create a data archive though HS Orka can track changes at Reykjanesvirkjun from year-to-year.