基于红外热成像技术的石窟壁面凝结水形成规律研究

凝结水会加剧石质文物的风化，以往确定凝结水量的实验设备布置复杂、监测范围有限，并且无法实时反映凝结状态，从而制约了对凝结水形成过程的认识以及对石质文物凝结水的有效防治。文章利用红外热成像技术开展凝结水形成规律研究，实现了对石窟壁面凝结水的大范围无损连续观测，并利用微波水分测试技术进行验证。针对一次降雨事件，对云冈石窟第19窟壁面进行了连续100 h的红外热成像监测，揭示了降雨前和降雨期间的壁面温度昼夜变化规律，通过对比空气露点温度识别出2个具备凝结水形成条件的时期:降温前凝结期，从降雨前16 h开始到降雨期间气温发生骤降为止；降温后凝结期，从气温骤降开始到降雨结束后12 h。同时，利用微波水分仪进行了连续56 h的浅表层岩石含水率动态监测，发现尽管壁面上无法用肉眼直接观察到凝结水，但岩石内部含水率增大，表明岩石内部已经优先凝结。降雨过程中气温在1 h内从18.5℃骤降到15.6 °C引起大气中的水汽凝结，导致露点温度下降，使得壁面不再具备凝结水形成条件。该研究对石质文物的凝结水防治具有重要的指导意义。

A study of the formation pattern of condensation water in grottoes based on the infrared thermal imaging technology

Condensation water can accelerate weathering of stone relics. Previous methods for detecting condensation water in grottoes have some shortcomings, such as the complex equipment layout and limited monitoring range, and are unable to reflect the real-time condensation state, which restrict the effective prevention and control of condensation water in grottoes. In this paper, the infrared thermal imaging technology, which can be used to obtain continuous and large-scale observation of temperature on the wall of grottoes, and the microwave moisture measurement technology, which can be used to obtain rock moisture inside the wall, are both used to study the formation mechanism of condensation water. During the occurrence of a rainfall event, a wall in cave 19 of the Yungang Grottoes was monitored by the infrared thermal imaging for 100 hours. This set of data reveals the diurnal variation pattern of temperature before and during the rainfall event, and two periods beneficial for the formation of condensation water were identified by comparing with the air dew point temperature. The two periods are the condensation period before cooling which starts from 16 hours before rainfall to a sudden drop of temperature during rainfall and the condensation period after cooling which starts from the sudden drop of temperature to 12 hours after the end of rainfall. At the same time, the dynamic monitoring of the shallow rock moisture content for 56 hours was carried out with a microwave moisture meter. Although condensation water cannot be directly observed on the wall, the microwave moisture meter shows that water content in the rock increases, indicating that water has been preferentially condensed inside the rock. It is also found that the sudden drop of air temperature (from 18.5 °C to 15.6 °C in 1 hour) during the process of rainfall causes the condensation of water vapor in atmosphere, which causes a significant decline in the dew point temperature, and the condition of condensation water formation is not fulfilled. This phenomenon is of important guiding significance for the prevention and control of condensation water.