Analysis of the Mapping Relationship Between Rock Infrared Emissivity and Brightness Temperature in Different Background Environments

The increase in thermal infrared brightness temperature and infrared emissivity observed during rock loading provides important insight into the physical mechanisms underlying thermal infrared anomalies associated with geological hazards, including earthquakes, landslides and rockbursts. However, the relationship between rock emissivity and brightness temperature is strongly influenced by the surrounding radiative environment, and how background radiation affects this relationship remains insufficiently understood. From the perspective of remote-sensing physics, this study investigates the influence of background radiation on the emissivity–brightness temperature relationship at the surfaces of multiple rock types. Experiments involving background-radiation measurements and rock-emissivity retrievals were conducted under different environmental conditions, and a physical relationship between background radiation and rock-surface brightness temperature was established. The results show that (1) the background radiation in the outdoor environment is mainly derived from the cold sky background, while the background radiation in the indoor environment tends to be close to the body radiation; and (2) in the indoor environment, the change in the emissivity is almost incapable of causing a brightness temperature response, and it is difficult to realize emissivity inversion, while in the outdoor environment, the mapping relationship between brightness temperature and emissivity is more relevant. Based on these findings, we developed an experimental configuration combining a movable chamber that opens to expose the loading platform to the sky with a multi-angle remote sensing observation loading platform designed to reduce structural obstruction. This configuration enables switching between enclosed and open-air conditions without relocating the loading platform and increases the contribution of cold sky background radiation to the radiation incident on the rock surface. The proposed experimental configuration may improve the reliability of laboratory thermal infrared rock-mechanics experiments and facilitate the investigation of stress-induced thermal infrared responses in rocks.