Surface Magnetic Resonance Tomography for Three-Dimensional Groundwater Using a Complex Model

In recent years, surface magnetic resonance tomography (MRT), which is applied to the direct determination of the presence of groundwater, has been developed from underground two-dimensional to three-dimensional (3D) imaging. However, because of the influence of subsurface electrical conductivity, the magnetic resonance sounding (MRS) signal has been proved to be a complex-valued form. Moreover, the real and imaginary parts of MRS signals show different sensitivities to aquifers of different depths. In this study, a complex model of 3D MRT with separated loops configuration is introduced to provide accurate water-bearing imaging. Through simulation experiments, we demonstrate that the separated loops configuration is conducive to obtaining the imaginary part signal of MRS. Compared with a conventional model, the complex model has better 3D imaging resolution and sensitivity, especially for the deep regions. Moreover, in the case of noise interference and the presence of a multi-aquifer, the imaging results of complex inversion are reliable. As a result, this study is significant to the further development of multi-channel MRS instruments and provides a feasible method for high-precision imaging.