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

应用地球物理学的电磁和电方法是研究浅层地下电导率结构的常用方法。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10千赫和1兆赫之间的频率范围内广播。传统RMT方法的一个显著缺点是在偏远地区缺乏可靠的高频源。另一个缺点是没有无线电发射机以低于10千赫的频率广播，这限制了渗透深度。为了克服这些限制，可以使用主动和可控源，而不是依赖于远程无线电发射机信号（CSRMT方法，1 kHz -1MHz）。在一些研究中，CSRMT方法成功地应用于浅层勘探。采用水平磁偶极子（HMD）和水平电偶极子（HED）两种方法。除了后勤和技术上的优势和劣势外，这些源在地面上产生不同的电流模式，具有不同的时空形状，导致不同的灵敏度模式。因此，不同的震源对地下电导率结构具有不同的分辨能力，可用于推导改进的地下各向异性模型。目前还没有针对1 kHz -1 MHz频段的此类CSRMT源进行系统细致的对比研究，包括三维数值模拟和先进的现场实验。为了解决EM勘探中的这一空白，我们提出以下目标：(1)制定最佳CSRMT测量的源场策略；我们经过测试的HED源将进一步发展为VMD和HMD；(2)为了得到改进的地下模型，一种新的三维CSRMT建模和反演-基于完善的ModEMM包-将扩展到所有来源；(3)考虑位移电流；(4)进一步开发准静态ModEMM代码以考虑各向异性；(5)为了验证新源，将在俄罗斯两个选定的地点进行新的现场实验。分析和数值模拟将用于优化测量策略和研究不同源的分辨率。现有的鲁棒CSRMT处理软件将用于推导全阻抗张量和倾卸传递函数。随后，现场数据将使用提出的改进和实现在ModEMM算法中进行三维倒转。伴随的敏感性研究将验证所考虑的源的分辨能力，并量化模型的改进，特别是在各向异性方面。

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.