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Development of a 2D adaptive finite element inversion algorithm for the marine Differential Electrical Dipole method

海洋差分电偶极子法二维自适应有限元反演算法的开发

基本信息

批准号：
389727048
负责人：
Dr. Amir Haroon
金额：
--
依托单位：
Ocean University of China
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2017
资助国家：
德国
起止时间：
2016-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/389727048?language=en
关键词：
Development 2D adaptive finite element

项目摘要

To increase the lateral resolution of a marine time-domain Controlled-Source Electromagnetic (TD-CSEM) application, the Institute of Geophysics and Meteorology (IGM), Cologne recently developed a novel seafloor-towed transmitter-receiver system called Differential Electric Dipole (DED). In the framework of a previous DFG project the novel DED method was developed and applied for the first time to study a sub-seafloor groundwater body near the coastline of Bat Yam, Israel. The application was effective in delineating the freshwater aquifer underneath the Mediterranean seafloor up to a distance of 3.6 - 3.7 km from the coastline.The acquired DED data set was interpreted using a 1D inversion approach, followed by a large-scale 2D modelling study that included over 400 000 forward calculations using the 3D finite difference forward algorithm for solving Maxwell's diffusion equations sldmem3t. Although the model parameter space was strongly simplified, the conducted calculations needed more than two months to complete. This interpretation approach is computationally expensive, biased, and needs to be replaced through the development of an efficient multi-dimensional (preferably 2D) TD-CSEM/DED inversion scheme.The proposed project aims to develop a fully functional finite element time-domain 2D inversion algorithm based on the existing frequency domain finite element forward algorithm of Li & Key (2007). The approach will be based on calculating the EM response for several frequencies in the frequency domain, followed by a transform into the time domain. The inversion scheme will include a global regularisation following Occam's razor to assure a smooth model inversion. The developments of the proposed project will justify future applications of the novel DED method in coastal regions to study freshwater aquifer systems. The 2D interpretation scheme is a necessary improvement for future applications, as DED exhibits an increased sensitivity towards multi-dimensional resistivity structures compared to the conventional HED source excitation. Furthermore, the bathymetry has a significant effect on DED data and needs to be sufficiently accounted for in the inversion scheme.

为了提高海洋时域可控源电磁（TD-CSEM）应用的横向分辨率，科隆地球物理与气象研究所（IGM）最近开发了一种称为差分电偶极子（DED）的新型海底拖曳发射机-接收机系统。在以前的DFG项目的框架内，开发了新的DED方法，并首次应用于研究以色列巴特亚姆海岸线附近的海底地下水体。该应用在描绘地中海海底下距离海岸线3.6 - 3.7 km的淡水含水层方面是有效的。使用一维反演方法解释了获得的DED数据集，然后是一个大的-大规模二维建模研究，包括使用三维有限差分正演算法求解麦克斯韦扩散方程sldmem3t的40多万次正演计算。虽然模型参数空间被大大简化，但进行的计算需要两个多月才能完成。这种解释方法计算量大，有偏差，需要通过开发一种有效的多维（最好是2D）TD-CSEM/DED反演方案来取代。所提出的项目旨在基于Li & Key（2007）现有的频域有限元正演算法开发一种功能齐全的有限元时域2D反演算法。该方法将基于在频域中计算几个频率的EM响应，然后变换到时域。反演方案将包括遵循奥卡姆剃刀的全局正则化，以确保平滑的模型反演。拟议项目的发展将证明新的DED方法在沿海地区研究淡水含水层系统的未来应用。2D解释方案是未来应用的必要改进，因为与常规HED源激发相比，DED对多维电阻率结构表现出更高的灵敏度。此外，测深有显着的影响DED数据，并需要充分考虑在反演方案。