Advancement of the capacitive resistivity method to estimate ice content in permafrost.

永久冻土是永久冻结的地面，主要存在于极地地区和高海拔山区。全球丰富的永久冻土对于生态、基础设施和地球的碳库存至关重要。在全球变暖的背景下，对永久冻土的测绘和观测变得越来越重要;地球物理学可以为这项任务做出重大贡献。折射地震法和直流电阻率法是最常用的方法，然而，它们在逻辑上很难应用于崎岖的地形。在本计画中，我们探讨电容电阻率法应用于多年冻土研究的可行性。代替金属棒的是电极片，其可以在不直接接触地面的情况下注入高频交流电。高频交流电流提供了确定电容率的机会，电容率构成了除了电导率之外的重要补充信息。在10 Hz和100 kHz之间的频率范围内，水冰的介电常数显示出特征频率依赖性，这将被用来估计冻结岩石中的冰含量。到目前为止，我们与制造商合作开发并测试了合适的设备。通过对测量阻抗的适当理论描述，我们在几个位置证明了在现场条件下可以测量介电常数的典型频谱。在这里，我们建议通过将该方法应用于几个具体问题来继续该项目。在瑞士的三个地点，这是经常调查的其他工作组和广泛的先验信息，我们将描述永久冻土体的内部结构，并估计冰含量。在西伯利亚的另一个地区，我们除了估算冰含量外，还将划定冻结和未冻结地面之间的边界，并绘制其横向变化图。该应用程序需要进一步的方法要求。在我们以前的实验中，穿透深度被限制在几米之内;我们打算尽可能地推动极限。特别是，我们将研究和避免电磁耦合效应的失真，这对更大的电极间距变得越来越重要。我们还将适应反演和解释方法的大带宽和大相位相移的阻抗相比，更传统的技术。

Permafrost ist permanently frozen ground that exists predominantly in polar regions and high-altitude mountains. The global abundance of permafrost is essential for ecology, infrastructure and the carbon inventory of the earth. In the context of global warming, the mapping and observation of permafrost occurence becomes increasingly important; a task where geophysics can make substantial contributions. Refraction seismics and DC resistivity methods are most frequently used, however, they can be logistically difficult to apply in rough terrain. In this project, we investigate the feasibility of capacitive resistivity for permafrost research. Instead of metal sticks, electrode sheets are being used, which may inject a high-frequency alternating current without direct contact to the ground. The high-frequency alternating current offers the opportunity to determine electrical permittivity, which constitutes important complementary information in addition to the electrical conductivity. In the frequency range between 10 Hz and 100 kHz, the permittivity of water ice displays a characteristic frequency dependence, which shall be exploited to estimate the ice content in frozen rocks. So far, we developed and tested suitable equipment in cooperation with the manufacturer. With an appropriate theoretical description of the measured impedance, we demonstrated at several locations that the typical frequency spectrum of permittivity may be measured under field conditions. Here, we propose to continue the project by applying the method to several specific problems. At three locations in Switzerland, which are frequently investigated by other working groups and where extensive a priori information is available, we will characterize the inner structure of the permafrost bodies and estimate the ice content. In another region located in Siberia, we will, in addition to the estimation of the ice content, delineate the boundary between the frozen and unfrozen ground and map its lateral variation. The application requires further methodological requirements. In our previous experiments, the penetration depth was limited to a few meters; we intend to push the limits as far as possible. In particular, we will investigatie and avoid distortion by electromagnetic coupling effects, which become increasingly important for larger electrode spacing. We also will adapt inversion and interpretation methods to the large bandwidth and the large phase phase shift of the impedance compared to more conventional techniques.