Aim of the project MoreSpin (Mobile Magnetic Resonance Sensor with supraconducting coil for prepolarization in the near surface soil) is to develop a mobile NMR instrument for detecting and mapping near-surface (2m) soil physical parameters. Supraconducting prepolarization coils and adiabadic excitation pulses will significantly improve signal quality.
The main focus of the project is on the development of a mobile NMR sensor that can be used to map the soil water content up to a depth of about 2 m. Moisture stored in near surface soils is key for a manifold of ecological processes. The soil, being the interface between the atmosphere and the lithosphere, plays a crucial role for the transport of water and the dissolved substances therein. At present, there are no suitable direct methods to determine soil moisture content at the required spatial and temporal length and time scales. Not only are direct methods on the km scale disproportionately involved, furthermore, the only available geophysical methods on this length scale are indirect methods and therefore highly ambiguous. One nondestructive geophysical surface method that is well established nowadays, is surface nuclear magnetic resonance or magnetic resonance sounding (MRS). However, MRS is not suitable to determine the near surface soil physical properties due to its lack of sensitivity in the first 2 m and the very time consuming investigation of large scale areas (km scale). Recently, promising theoretical concepts have been published that allow to deduce the development of a NMR based sensor that meets the required properties in terms of measurement progress and sensitivity. The idea of a suitable mobile MRS sensors is based on a superconducting coil that is used to prepolarize the near surface subsoil in conjunction with adiabatic excitation pulses and a small scale receiver unit.
On the one hand prepolarization aims at an increase in macroscopic magnetization, whereas on the other hand adiabatic pulses guarantee an evenly excitation of the NMR signal. Both approaches combined, increase the measured NMR signal by more than an order of magnitude. Using punctiform receivers enables high resolution mapping of soil physical properties. The new mobile MRS sensor would allow to nondestructively map soil moisture content in several characteristic depths (topsoil, root zone, subsoil) on the km scale. The sensor to be developed, has the potential to create new scientific analyzing methods in various geoscientific research areas ranging from solute transport in the context of permafrost and climate models up to questions of groundwater recharge, soil protection and safe food supply.