Rock Emissivity Measurement for Infrared Thermography Engineering Geological Applications

Abstract

Infrared thermography is a growing technology in the engineering geological field both for the remote survey of rock masses and as a laboratory tool for the non-destructive characterization of intact rock. In this latter case, its utility can be found either from a qualitative point of view, highlighting thermal contrasts on the rock surface, or from a quantitative point of view, involving the study of the surface temperature variations. Since the surface temperature of an object is proportional to its emissivity, the knowledge of this last value is crucial for the correct calibration of the instrument and for the achievement of reliable thermal outcomes. Although rock emissivity can be measured according to specific procedures, there is not always the time or possibility to carry out such measurements. Therefore, referring to reliable literature values is useful. In this frame, this paper aims at providing reference emissivity values belonging to 15 rock types among sedimentary, igneous and metamorphic categories, which underwent laboratory emissivity estimation by employing a high-sensitivity thermal camera. The results show that rocks can be defined as “emitters”, with emissivity generally ranging from 0.89 to 0.99. Such variability arises from both their intrinsic properties, such as the presence of pores and the different thermal behavior of minerals, and the surface conditions, such as polishing treatments for ornamental stones. The resulting emissivity values are reported and commented on herein for each different studied lithology, thus providing not only a reference dataset for practical use, but also laying the foundation for further scientific studies, also aimed at widening the rock aspects to investigate through IRT.

UAV-Based Photogrammetry and Infrared Thermography Applied to Rock Mass Survey for Geomechanical Purposes

“…It exploits the thermal radiation emitted by matter, which travels with wavelengths mainly falling within the Infrared band of the electromagnetic spectrum (0.1-100 µm). The Stefan-Boltzmann law explains that the emissivity of an object is directly proportional to its temperature; therefore, it is possible to estimate its surface temperature by employing specific devices called thermal cameras if the characteristic emissivity value of the framed subject is known [16]. The application of IRT on rock masses returned satisfactory results in detecting open fractures [17], weathered rock sectors [18], the integrity of rock [19], the presence of rock bridges [20] and, more generically, in supporting rock stability studies, e.g., [21][22][23], even in both post-rockfall emergency [24] and underground settings [25].…”

Slope-Scale Remote Mapping of Rock Mass Fracturing by Modeling Cooling Trends Derived from Infrared Thermography

“…Thus, for a blackbody, ε = 1, while grey bodies have (ε < 1) [69,70]. For example, metals usually exhibit very low emissivity (ε < 0.1), while rocks generally have high emissivity (ε > 0.9); [71,72]. Atmospheric transmittance represents the absorptivity of the atmosphere and depends on air humidity, temperature and distance of IR thermal camera.…”

Thermal monitoring and deep learning approach for early warning prediction of rock burst in underground structures

“…The technique provides easily interpretable data in the form of images or videos, and poses no risk of radiation exposure from the hazardous sources (Yang et al 2014). Several research (Luong 1990, Freund et al 2007, He et al 2009, Mineo et al 2021 have been conducted to investigate the infrared (IR) characteristics of rocks under both static and dynamic loading conditions. Prior to the occurrence of failure, IR anomalies were prominently observed within the region of damage, as documented in the literature (Wu and Wang 1998, Wu et al 2000, Sheinin and Blokhin 2012.…”