Tensor 3D interpretation of CSRMT data with novel high-frequency sources considering displacement currents and anisotropy

应用地球物理的电磁和电学方法是研究浅层地下电性结构的常用方法。在过去的几十年里，无线电大地电磁(RMT)方法得到了广泛的应用，并成功地应用于各种环境、工程和其他勘探问题。传统的RMT方法使用军用和民用无线电发射机，在10 kHz到1 MHz的频率范围内广播。传统的RMT方法的一个显着缺点是在偏远地区缺乏健壮的高频源。另一个缺点是，没有无线电发射机以10千赫以下的频率广播，这限制了穿透深度。为了克服这些限制，可以使用有源和受控源，而不是依赖远程无线电发射机信号(CSRMT方法，1 kHz-1 MHz)。在几项研究中，CSRMT方法成功地应用于浅层勘探。同时使用水平磁偶极子(HMD)和水平电偶极子(HED)。除了后勤和技术上的优势和劣势，这些源在地面上产生不同模式的电流，具有不同的时空形状，导致不同的灵敏度模式。因此，不同的源具有不同的关于地下电导率结构的分辨率，并且可以用于推导改进的地下各向异性模型。目前，还没有对这种CSRMT源在1 kHz-1 MHz频段进行系统和详细的比较研究，包括三维数值模拟和先进的野外实验。为了解决EM勘探中的这一差距，我们提出了以下目标：(1)开发用于最佳CSRMT测量的源场策略；我们经过良好测试的HED源将进一步发展为VMD和HMD；(2)为了获得改进的地下模型，基于成熟的MODEMM程序包的新的3D CSRMT建模和反演将扩展到所有震源；(3)为了考虑位移电流和(4)为了进一步考虑各向异性(5)为了验证新震源的各向异性，将在俄罗斯的两个选定地点进行新的野外实验。分析和数值模拟将用于优化测量策略和研究不同震源的分辨率。现有的强大的CSRMT处理软件将用于推导全阻抗张量和翻车机传递函数。随后，将使用所提议的改进和在MODEMM算法中的实现来在3D中反演场数据。随之而来的灵敏度研究将验证所考虑的震源的分辨率，并量化模型的改进，特别是关于各向异性的改进。

Electromagnetic and electric methods of applied geophysics are commonly used to study the conductivity structure of the shallow subsurface. In the past decades the radio-magnetotelluric (RMT) method has gained popularity and was successfully applied to various environmental, engineering, and other exploration problems. The conventional RMT method uses military and civilian radio transmitters broadcasting in the frequency range between 10 kHz and 1MHz. A significant disadvantage of the traditional RMT method is the lack of robust high-frequency sources in remote areas. Another drawback is the fact that there are no radio-transmitters broadcasting at frequencies below 10 kHz which limits the penetration depth. To overcome these limitations, active and controlled-sources can be used instead of depending on remote radio-transmitter signals (CSRMT method, 1 kHz –1MHz). In several studies, the CSRMT method was successfully applied to shallow exploration. Both, horizontal magnetic (HMD) and horizontal electric dipoles (HED) were used. Besides logistical and technical advantages and disadvantages, these sources generate different modes of currents in the ground and have different spatial-temporal shapes leading to different sensitivity patterns. As a consequence, different sources have a different resolving power regarding the subsurface conductivity structures and can be utilized to derive improved anisotropic models of the subsurface. Currently, no systematic and elaborate comparative studies of such CSRMT sources exist for the frequency band of 1 kHz –1 MHz, including 3D numerical modeling and advanced field experiments. To tackle this gap in EM exploration, we propose the following objectives: (1) to develop source field strategies for optimal CSRMT surveying; our well-tested HED source will be further developed into VMD and HMD; (2) to derive improved subsurface models a novel 3D CSRMT modelling and inversion - based on the well-established ModEMM package - will be extended to all sources; (3) to take into account the displacement currents and (4) to develop the quasi-static ModEMM code further to consider the anisotropy (5) to validate the new sources, novel field experiments at two selected sites in Russia will be conducted.Analytical and numerical simulations will be used to optimize surveying strategies and to study the resolution power of different sources. Existing robust CSRMT processing software will be used to derive full impedance tensor and tipper transfer functions. Subsequently, the field data will be inverted in 3D using the proposed improvements and implementations in the ModEMM algorithm. Accompanying sensitivity studies will validate the resolving power of the considered sources and quantify the improvements on the models, particularly with respect to anisotropy.