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

永久冻土是指主要存在于极地地区和高海拔山区的永久冻土。全球丰富的永久冻土对生态、基础设施和地球的碳储量至关重要。在全球变暖的背景下，多年冻土带的测绘和观测变得越来越重要；地球物理学可以作出重大贡献的任务。折射地震和直流电阻率法是最常用的方法，然而，它们在崎岖地形中应用起来很困难。在本项目中，我们探讨了电容电阻率在多年冻土研究中的可行性。代替金属棒的是电极片，它可以注入高频交流电而不直接接触地面。高频交流电提供了确定介电常数的机会，这是除电导率之外的重要补充信息。在10 Hz ~ 100 kHz的频率范围内，水冰的介电常数表现出频率依赖的特征，可以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和测试了合适的设备。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这个项目。在瑞士的三个地点，我们将描绘永久冻土层的内部结构，并估计冰含量，这些地点经常由其他工作组进行调查，并且有广泛的先验信息可用。在西伯利亚的另一个地区，除了估算冰含量外，我们还将划定冻土和未冻土之间的边界，并绘制其横向变化图。应用程序需要进一步的方法要求。在我们之前的实验中，穿透深度被限制在几米；我们打算尽可能地突破极限。特别是，我们将研究和避免电磁耦合效应造成的畸变，这在更大的电极间距中变得越来越重要。与更传统的技术相比，我们还将适应大带宽和大相移阻抗的反演和解释方法。

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.