Monitoring the thermal state of permafrost by automated time-lapse capacitive resistivity imaging

对地下过程的长期监测越来越依赖于由创新的现场传感器进行的智能、系统的数据收集。拟议项目的目的是开发一种新的技术概念，用于非侵入性体积成像和对多年冻土热状态的常规时间监测。在世界气象组织(WMO)全球气候观测系统(GCOS)的监测框架内，多年冻土被确定为全球气候变化的六个冰冻圈指标之一。随着孔隙水的冻结或融化，永久冻土温度的变化会导致电阻率的显著变化。利用四维电阻率层析成像(ERT)可以实现对电阻率变化的非侵入性评估和体积监测。具有适当的空间和时间分辨率的层析重建能够直观地显示，并为定量分析冻结和融化过程打开了重要的机会，包括校准永久冻土温度。然而，尽管传统的ERT方法具有广泛的吸引力，但电气传感器需要与地面进行电流耦合。在多年冻土地区，金属电极必须物理地植入活跃层，这是季节性冻结和融化的结果。这可能会导致现场测量的重大实际限制，因为传感器与宿主基岩、土壤或建筑材料之间的接触电阻在冻结和融化时水平很高，而且变化很大。使用一种新的电容耦合ERT方法，我们建议论证使用永久性的现场电容传感器进行时间推移层析成像测量的技术可行性，以远程监测永久冻土的热状态。这将大大提高监测能力，无论是对实验室中的多年冻土模拟实验，还是对现场的实际应用。这项工作将包括数值模拟，以确定实地和实验室规模的体积成像和长期监测永久冻土所需的最佳分布式电容式传感器网络。在此基础上，设计了用于多传感器自动延时数据采集的测量系统，并为实验室原型系统建立了可行的体系结构。随后，将开发一个功能台式样机，并将论证多传感器数据采集和自动化操作的技术可行性。最后，我们将在模拟基岩中永久冻土生长、持续和融化的受控实验室实验中验证进行自动延时温度校准CRI测量的概念。

Long-term monitoring of subsurface processes increasingly relies on intelligent, systematic data collection by innovative field sensors. The aim of the proposed project is to develop a new technology concept for the non-invasive volumetric imaging and routine temporal monitoring of the thermal state of permafrost. Permafrost has been identified as one of six cryospheric indicators of global climate change within the monitoring framework of the World Meteorological Organization (WMO) Global Climate Observing System (GCOS). Changes in permafrost temperature, associated with the freezing or thawing of pore water, result in significant changes in electrical resistivity. Non-invasive assessment and volumetric monitoring of resistivity changes are facilitated by 4D Electrical Resistivity Tomography (ERT). Tomographic reconstruction with appropriate spatial and temporal resolution enables intuitive visualisation and opens up the important opportunity for quantitative analysis of freeze and thaw processes, including the calibration to permafrost temperature. However, despite the broad appeal of conventional ERT methodology, electrical sensors require galvanic coupling with the ground. In permafrost regions, metal electrodes must be physically implanted into the active layer, which is subject to seasonal freezing and thawing. This can lead to significant practical limitations on field measurements due to high levels of and large variations in contact resistances between sensors and the host bedrock, soil or building material as it freezes and thaws. Using a novel capacitively-coupled ERT approach, we propose to demonstrate the technical feasibility of undertaking time-lapse tomographic measurements using permanent, in-situ capacitive sensors to remotely monitor the thermal state of permafrost. This will lead to significant improvements in monitoring capability, both for permafrost simulation experiments in the laboratory and for practical applications in the field. The work will include numerical simulation to determine optimal distributed capacitive sensor networks required for volumetric imaging and long-term monitoring of permafrost, both at the field and at the laboratory scale. Based on the results, a measurement system for multi-sensor automated time-lapse data acquisition will be designed and a viable architecture for a laboratory prototype system will be established. Subsequently, a functional benchtop prototype will be developed and technical feasibility of multi-sensor data acquisition and automated operation will be demonstrated. Finally, we will validate the concept of making automated time-lapse temperature-calibrated CRI measurements in controlled laboratory experiments that simulate permafrost growth, persistence and thaw in bedrock.