Inversions Of Surface-Nmr Signals Using Complex Kernels1

The SNMR (Surface Nuclear Magnetic Resonance, also called MRS - Magnetic Resonance Sounding)<br>method is used for direct groundwater exploration and improved aquifer characterization with measurements<br>on the surface. Since the electrical conductivity of the subsurface alters the SNMR amplitude<br>and especially the phase, the conductivity structure must be known before the inversion of the SNMR<br>amplitudes. This study demonstrates the effect on the water content determination if the electrical conductivity<br>is not considered. Disregarding the electrical conductivity results into significant wrong water<br>content distributions even at moderate resistivities of 100 ­m. The conductivity must be taken into account<br>down to an appropriate depth, also structures below the assumed penetration depth of 100 m can<br>effect the water content determination. Non considering conductive structures above or in the aquifer results<br>into an underestimation and downward shift of the inverted water bearing layer; conductive media<br>below the aquifer lead to an overestimation of the water content. For real data, both amplitude and phase<br>values should agree with modeled data. Analyzing the SNMR phase values of real data provides additional<br>information for estimating the reliability of the inversion result.