Abstract
Previous studies have shown that thermal infrared radiation (TIR) changes with stress for loaded rocks. TIR changes were mainly attributed to temperature change without considering the change in surface emissivity. And it remains unclear whether there was a change in emissivity during the rock loading process. Therefore, based on the spectral radiance observations in this paper, an experimental study involving the emissivity variation in the 8.0–13.0 μm range for elastic loaded quartz sandstone under outdoor conditions was conducted. The experiments yield the following results. First, a variation in the stress condition led to the emissivity change in addition to the temperature change. The spectral radiance change was the combined result of the temperature changes and emissivity changes. Second, the emissivity changes linearly with the stress change, and the amplitude is relatively large in the 8.0–10.0 μm range. The waveband features of emissivity variation are the main factor leading to the waveband features of stress-induced radiance change. Third, the explanations for the changes in temperature and emissivity during loading process are analyzed. And the significance and difficulty for further satellite remote sensing purpose is discussed. The experimental results provide an experimental foundation for crustal stress field monitoring.
Highlights
Earthquakes are one of the most unexpected and most serious natural disasters
Some explanations for the thermal infrared radiation (TIR) anomalies were proposed, such as rising fluids that could lead to the emanation of warm gases [1], the “local greenhouse” effect caused by the diffuse CO2 [2,3,7], rising well-water levels and changing moisture contents in the soil [13], latent heat due to condensation of water on air ions formed as the result of radon emanation [14,15], the TIR change caused by the stress change [6,16], and charge generation and propagation in igneous rock with “P-holes” [9,10,17]
As this study focused on the temperature change in the elastic stage and the experimental condition was relatively stable during the loading process, the measured temperature change is mainly related to the stress change, f 1(t)
Summary
Earthquakes are one of the most unexpected and most serious natural disasters. In recent years, frequently occurring disastrous earthquakes, including the Wenchuan Earthquake (M 8.0, 2008), Chile earthquake (M 8.8, 2010), and Nepal earthquake (M 8.1, 2015), have killed thousands of people and caused massive losses. In 1988, Gorny et al [1] used satellite technology to observe short-lived thermal infrared radiation (TIR) anomalies before a strong earthquake in Central Asia. The scientific community has since reported a large number of TIR anomalies occurring before many medium-to-large (M > 5.5) earthquakes all over the world, and this phenomenon has been repeatedly verified all over the world during the past two decades [2,3,4,5,6,7,8,9,10,11,12]. The use of thermal infrared remote sensing for monitoring pre-earthquake anomalies at a broadly spatial and continuous temporal scale has become a popular topic in seismic monitoring research.
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