COMET

The Project targets on providing an inversion algorithm structural coupling Magnetic Resonance Tomography and Electrical Resistivity Tomography. This includes the implementation of an efficient calculation of magnetic fields based on arbitrary 2D resistivity distributions.

Water belongs to the natural resources that deserves protection and increasing diverse demand worldwide. Thus, detailed exploration and characterization of aquifers becomes more and more important and hydrogeophysical methods can contribute. Among the available methods, Electrical Resistivity Tomography (ERT) and Surface Nuclear Magnetic Resonance (SNMR) have proven to yield important parameters. A combination of both techniques can provide water content, hydraulic conductivity and salinity.

While 2D ERT is state-of-the-art since 15 years, 2D SNMR or MRT (Magnetic Resonance Tomography) has developed recently. The recent development of multi-channel devices and more efficient loop setups, the time to acquire a full MRT  dataset has become more and more acceptable. However, the 2D datasets yield to the question of a suitable inversion algorithm for analyzing the data. In the context of 2D ERT models, joint inversion algorithms have been investigated in 1D, but none accounts for an arbitrary 2D resistivity distribution, except as a prerequisite to the modelling of the magnetic field.

We project COMET not only target to account for arbitrary 2D resistivity distribution but will develop a structurally coupled 2D inversion that  is expected to help reducing the uncertainties, as well as to improve the resolution of the inversion result and thus  provides valuable input to hydraulic modelling. Consequently, the results of the combined inversion will be 2-D images of the parameters resistivity, water content and relaxation time.

Our forward modeling implementation can deal with arbitrary transmitter and receiver shapes. The semi-analytical solution for a 1D layered earth is used as primary field for the subsequent finite element modeling.

The derived magnetic fields are the used for the calculation of the NMR sensitivity function (kernel) with correlates changes in the data to changes in water content and relaxation times, respectively. This information finally is used for inversion of the NMR measurements.

The development of the code basis is done solely using of open-source projects and will in the end be published in the sense of reproducible and sustainable science.