Measuring Soil Moisture Using Surface-NMR With Prepolarization

Summary Small-scale investigations of the unsaturated zone has gained increasing interest in the hydro-geophysical research community. The technique of surface-NMR (SNMR), while providing valuable data on water content and permeability in the saturated zone, has difficulties to reliably detect and interpret signals from partly-saturated soils due to low signal amplitudes. Recently, SNMR using prepolarization (SNMR-PP) has gained interest to overcome this limitation. Here, a strong prepolarization field enhances the SNMR signal of coils with a footprint of below 1m up to a level that promises to enable soil moisture measurements in the upper two meters of the subsurface in the near future. We present the first SNMR-PP measurements on a real soil and demonstrate the general feasibility of this technique to qualitatively and quantitatively detect soil moisture. Our soil moisture measurements are validated by independent time domain reflectometry (TDR) data.