Remote Detection of Thermal Anomalies for Geothermal Exploration. How Well Does It work?

Abstract

Surface manifestations are an indicative sign of the geothermal activity in the subsurface. By far not all geothermal systems develop surface manifestations but where they are present, they are a good starting point for early stage exploration efforts. Hence, it is crucial to have a technique that can successfully and reliably detect and map (and possibly monitor) surface manifestations. Remote sensing has the potential to support the mapping of such geothermal surface manifestations, including deposited and altered mineralization and temperature anomalies. In particular, thermal infrared bands of multispectral satellite sensors, for example, have been shown to be effective in detecting surface temperature anomalies in ideal circumstances. Practical experience with thermal infrared data, however, often shows a more complex situation: thermal anomalies appear subdued in satellite data with only moderate spatial resolution (e.g. ASTER @ 90 metres) and are not easily discriminated from false anomalies that are created by solar heating and differences in e.g. land cover, rock properties or soil/vegetation moisture. Night time acquisitions suppress these false anomalies only partially since the acquisition time of most satellite sensors (e.g. ASTER @ 10.30pm local time) is too early in the night for the temperatures of the surrounding strata to have reached an equilibrium. In this paper we highlight some of the factors that influence the process of anomaly detection, compared to ground to airborne temperature measurements of thermal anomalies in a controlled test site area. We also introduce the new higher spatial resolution and multi-temporal ECOSTRESS sensor (JPL/NASA) as a possible step forward in the future detection of geothermal temperature anomalies.