Improved ice quantification at alpine permafrost sites based on electrical and electromagnetic measurements of spectral induced polarization

基于光谱诱发极化的电学和电磁测量改进高山永久冻土区的冰量化

• 批准号: 403089687
• 负责人: Professor Dr. Andreas Kemna
• 金额: --
• 依托单位: Department of Geosciences
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2018
• 资助国家: 德国
• 起止时间: 2017-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/403089687?language=en
• 关键词: Improved; ice; quantification; alpine; permafrost

Mountain permafrost is currently undergoing substantial changes due to climate change, and consistent warming and thawing has been observed at many sites worldwide. As permafrost and especially its ground ice content can neither be assessed visually from the surface nor by standard remote sensing techniques, geophysical methods are increasingly being used to investigate the spatio-temporal dynamics of permafrost. In particular electrical resistivity tomography (ERT) has been proven a suitable tool to characterize and monitor permafrost occurrences. However, since the resistivity of rocks depends not only on ice/water content but also on porosity, pore connectivity, mineralogy, water chemistry and temperature, it is hardly possible to reliably quantify ice content from ERT measurements.Utilizing the fact that ice exhibits a characteristic electrical polarization signature, we propose a new geophysical methodology for the imaging and quantification of subsurface ice content at alpine permafrost sites based on the spatially resolved measurement of spectral induced polarization (SIP). Corresponding to the frequency range in which ice shows a maximum polarization (100 Hz to 100 kHz), we plan to complement direct SIP measurements by indirect SIP measurements by means of the time-domain electromagnetic induction method (TEM), in order to compensate a possible lack of information in the direct SIP measurements at higher frequencies. The SIP spectrum will be described as a superposition of the background signal and the characteristic ice response, and ice content will be determined on the basis of a newly developed petrophysical model of the SIP properties of (partially) frozen rocks.The proposed new methodology for the quantitative, spatially resolved determination of ice content will be tested at selected sites in the Alps with typical alpine permafrost characteristics, where independent information for calibration and validation is available from previous geophysical investigations and existing monitoring data. The involved petrophysical model will be validated by means of SIP laboratory measurements in the course of controlled freeze-thaw experiments on rock samples from the considered field sites, which will be independently analyzed for relevant model parameters.To our knowledge the project represents the first comprehensive study on the quantitative imaging of subsurface ice content in alpine permafrost terrain based on combined SIP/TEM measurements. While the laboratory studies and the petrophysical model development contribute to an improved fundamental understanding of the electrical properties of (partially) frozen porous media, by considering various types of alpine permafrost occurrences the field studies are highly relevant with a view to an effective permafrost monitoring in the context of global warming.

由于气候变化，山地永久冻土目前正在发生重大变化，在世界各地的许多地点都观察到持续的变暖和融化。由于永久冻土，特别是其地面冰含量既不能从地面直观地评估，也不能通过标准的遥感技术进行评估，地球物理方法正越来越多地用于调查永久冻土的时空动态。特别是电阻率层析成像（ERT）已被证明是一个合适的工具，以表征和监测冻土发生。然而，由于岩石的电阻率不仅取决于冰/水含量，还取决于孔隙度、孔隙连通性、矿物学、水化学和温度，因此几乎不可能从ERT测量中可靠地量化冰含量。我们提出了一种新的地球物理方法，根据光谱的空间分辨测量，对高山永久冻土区的地下冰含量进行成像和量化。激发极化（SIP）。对应于冰显示最大极化的频率范围（100 Hz至100 kHz），我们计划通过时域电磁感应法（TEM）间接SIP测量来补充直接SIP测量，以补偿在更高频率下直接SIP测量中可能缺乏的信息。SIP频谱将被描述为背景信号和特征冰响应的叠加，冰含量将根据新开发的SIP特性的岩石物理模型确定，（部分）冻结的岩石。将在阿尔卑斯山具有典型高山永久冻土特征的选定地点测试拟议的定量、空间分辨测定冰含量的新方法，其中可从先前的地球物理调查和现有监测数据中获得用于校准和验证的独立信息。所涉及的岩石物理模型将通过SIP实验室测量在控制冻融实验的过程中对岩石样品从所考虑的现场站点，这将是独立的分析相关的模型parameters.To我们所知的项目代表了第一个全面的研究，定量成像的地下冰含量在高山永久冻土地形的基础上结合SIP/TEM测量。虽然实验室研究和岩石物理模型的开发有助于改善（部分）冻结多孔介质的电性能的基本理解，通过考虑各种类型的高山永久冻土发生的实地研究是高度相关的，以期在全球变暖的背景下有效的永久冻土监测。