Infrared imaging of thermal areas

Abstract

Heat discharges at the surface from thermal features such as hot springs, fumaroles and steaming ground. An understanding of discharging heat is important for geothermal exploration, as it provides a guide to the geothermal power potential of the reservoir. One way to determine the amount of heat discharging in active thermal areas is to measure the temperature of the surface features. In three New Zealand geothermal fields, we measured temperatures of surface manifestations using: 1) a temperature probe, 2) an infrared thermometer, and 3) an infrared camera. Using all three techniques we documented the temperatures in 12 alkali chloride hot springs and channels, six acid sulfate hot springs, six mud pools, nine areas of steaming ground and seven fumaroles. This enabled a direct comparison of the temperatures obtained using the different techniques for each feature type. Our study revealed that regardless of which measuring device was used, the temperatures measured in hot spring pools and channels showed minimal variation. In fumaroles and steaming ground areas, the correlation between temperature measuring devices was not as consistent. However, there was minimal temperature variation when we were within one meter of the steam features and when we altered the emissivity value to account for the higher reflectance due to the discharging steam. Our infrared camera enabled the quick identification of sites with increased temperature that were not easily accessible. It was also ideally suited for mapping the location of micro-fractures and vents that discharged heat and were not otherwise visible. Infrared imaging enables the mapping of subtle temperature differences establishing surface thermal gradients profiles. Alignment and orientation of areas discharging a higher-than-ambient temperature are also easily mapped. Infrared imaging of heat flow migration pathways contributes to the development of a conceptual model of a geothermal system.