Enhancing Geo-electric Exploration using Thermal Remote Sensing and Dual Band Processing – Case Study of the Stromboli Volcano (Aeolian Islands)

Geo-electric exploration surveys such as Electrical Resistivity Tomography (ERT) can provide valuable insights regarding the characterization of geological structures and hydrothermal systems in volcanic environments. However, while ERT is a powerful tool, its effectiveness can be limited by the inherent sensitivity of rock electrical conductivity to various parameters. These can include factors such as water content, salinity of pore water, rock temperature, or alteration. Each of these factors significantly impacts the results of an ERT survey and, if not precisely characterized, can lead to inaccurate data interpretation. As a result, ERT is often supplemented by additional costly and time-consuming in-situ measurements, such as soil temperature or diffuse soil CO₂ degassing probing, to provide a more comprehensive analysis of subsurface conditions.

The purpose of this study is to summarize the recent geophysical findings from Revil et al. (2023), where they constructed the first 3D electrical conductivity model of the Stromboli volcano in the Aeolian Islands. To build this model, Revil et al. collected and analyzed data from various sources, including self-potential, soil temperature, soil CO₂ degassing, and thermal remote sensing maps. By comparing these complementary datasets, this study aims to highlight the benefits of using Thermal Remote Sensing as a supplementary tool to analyze data from subsurface geo-electric exploration. Thermal remote sensing constitutes a practical and cost-efficient approach, allowing for systematic monitoring of Earth’s surface thermal anomalies via infrared imaging down to a spatial resolution of 30 to 15 meters.  By applying corrections and isolating surface-emitted radiance from the integrated signature received by the satellite, the average temperature of the surface is retrieved for each pixel. Thermal anomalies on the volcano are then located, and their temperatures are accurately determined through dual-band processing, which involves comparing images from Thermal Infrared and Short-Wave Infrared spectra.

The maximum remotely recorded infrared temperature is 792°C, associated with the main active volcanic vents. Considering the extreme heterogeneity in surface temperature at the scale of the pixel as well as the presence of volcanic gases, uncertainties for the remotely acquired temperature are in the range of a few degrees centigrade. The soil temperature measurements near these vents, retrieved at a depth of 30 cm, also reveal significant internal activity with temperature values reaching 100°C (the readings were taken to a tenth of a degree). This high-temperature region perfectly matches the positive anomalies of self-potential and diffuse soil CO₂ degassing associated with the vertical conductive channel (1 to 10^-1 S/m).

In conclusion, the ability to isolate the temperature associated with the thermally active component makes this approach highly promising for accurately constraining the spatial distribution of the shallow hydrothermal system, as it is manifested at the surface by high-temperature areas. Therefore, thermal remote sensing appears very useful in refining the interpretation of subsurface geophysical images.