Two-dimensional inversion of Magnetic Resonance Sounding data incorporating structural orientation information

Abstract:

Magnetic resonance sounding (MRS) is a geophysical method that can directly detect and evaluate groundwater. In recent years, with the development of theory and applications, MRS instruments capable of imaging two-dimensional (2-D) targets have become commercially available, which put forward higher requirements for the resolution of MRS measurement. The parameters obtained from the MRS method are the water content and distribution of groundwater. Under the influence of gravity and underground structure, the distribution of groundwater may have an obvious dominant direction in many cases, such as the water-bearing stratum and fault. If the structural orientation information were incorporated in the inversion process, the issue of multiple solutions can be greatly reduced and the inversion accuracy can be improved. In this paper, the method for generating spatial gradient operators on unstructured meshes is developed, which provides feasibility to incorporate the structural orientation information in 2-D Occam’s inversion of MRS data. We constructed a theoretical model of the 2-D underground aquifer with an obvious dominant direction, and the validity of the spatial gradient operators on unstructured meshes is proved by the inversion of the theoretical MRS signal. The results show that the inversion effect under the constrain of spatial gradient operators is improved compared with the traditional minimum-model constraints. The data fitting difference converges faster and reaches a smaller value. The validity and feasibility of the method are also verified by the inversion of the filed MRS data.