Steady-State Surface NMR for Mapping of Groundwater

Groundwater is a critical freshwater source for billions of people (Klee, 2013), but resources are increasingly stressed by climate change, pollution, and overexploitation (Frappart & Ramillien, 2018, ). Locating groundwater sources and monitoring their sustainable use is a difficult task. One method that shows great promise is surface nuclear magnetic resonance (NMR), as it is the only technique capable of non-invasive direct measurements of subsurface water content and pore-space properties. Unfortunately, surface NMR often suffers from low-amplitude signals that limit mapping speeds and may prohibit measurements in noisy environments. We demonstrate a steady-state scheme for surface NMR, enabled by recent breakthroughs in transmitter capabilities and numerical modeling that delivers orders of magnitude signal enhancements. The new technique is a highly efficient measurement that is both narrowband and utilizes the full measurement interval in contrast to traditional approaches. Our results demonstrate that high-fidelity groundwater measurements are now possible in hitherto inaccessible areas.