IMPROVING THE SPATIAL RESOLUTION OF SURFACE NMR FOR IMAGING THE UNSATURATED ZONE
Surface NMR employs a wire loop on the ground surface to make a non-invasive NMR measurement of the subsurface. The primary focus of our research is the challenge of acquiring sufficient vertical resolution in studies of the top few meters or tens of meters of the unsaturated zone. We are exploring the use of novel data acquisition techniques designed to provide improved resolution in the water content and relaxation time depth profiles estimated in surface NMR. Using excitation schemes that generate a complex NMR signal, we are able to employ the real and quadrature components to spatially sample the subsurface in different ways; effectively allowing us to perform two soundings in a single measurement. This strategy is able to better reproduce water content and relaxation time contrasts, and identify fine-scale structures in the shallow subsurface (<12 m). This represents an important advancement in the surface NMR method, producing acquired images that more accurately reflect the subsurface properties and structure.