Geothermal Exploration at Pilgrim Hot Springs, Alaska, Using Airborne Thermal Infrared Remote Sensing

Abstract

The Department of Energy (DOE) and the Alaska Energy Authority are jointly funding a project to re-assess the resource potential of the Pilgrim Hot Springs geothermal system in western Alaska. Phase one of this project has included airborne thermal infrared remote sensing for mapping surface geothermal phenomena and assessment of the resource potential of the system. Thermal infrared and optical images were acquired over the Pilgrim Hot Springs site and neighboring regions during two surveys in fall 2010 and spring 2011. Thermal images providing information on land surface temperature at a spatial resolution better than 1.3 meters were acquired using a FLIR A320 camera operating in the broad 7.5?13 ?m wavelength region. Fieldwork during the airborne surveys gathered ground calibration and validation data such as hot spring, ground, and atmospheric temperatures, atmospheric humidity and the precise GPS locations of low-emissivity ground targets. We applied atmospheric correction, registration and mosaicking to generate seamless maps of calibrated surface temperature across the study area. Analysis of this data enables delineation of the main geothermal features of the system including hot springs, pools, and areas of thermally anomalous ground. Using a thermal-budget approach the thermal heat ?ux sustaining surface geothermal waters was estimated from the fall and spring FLIR data. Calculated heat ?uxes and out?ow rates assuming a hot spring temperature of 81°C is signi?cantly higher than previous ?eld-based methods. Our work demonstrates that airborne thermal infrared remote sensing provides a rapid and relatively low cost method for mapping and quantitative assessment of undeveloped spring-dominated geothermal systems in Alaska.