Noise Cancellation for Surface NMR - Derivation of Time and Frequency Domain Approaches

Even though surface nuclear magnetic resonance (surface NMR) is the only geophysical technique that provides hydrogeophysical rock properties on the base of direct sensitivity to subsurface water, in many cases surface NMR measurements suffers bad signal-to-noise ratio, and measurements can be carried out only far from sources of electromagnetic noise. To overcome these restriction some approaches using a reference loop based system were developed during the last years (Radic, 2006; Walsh, 2008; Müller-Petke and Yaramanci, 2010; Neyer, 2010). All approaches have demonstrated useful capability to improve S/N. But a comparison that allows for determining properties, i.e., pro and contra of each approach is missing. Thus, to compare time domain with the frequency domain approach, we developed an own frequency domain code beside the existing time domain code. We present a complete derivation of both the time and frequency domain reference technique. Both allow for single and arbitrary number of reference loops. This gives insight into the common idea of both but also the differences in final equations and realization. Finally, this development enables to compare important properties such as applicability at different noise conditions or numerical costs (Müller-Petke and Yaramanci, 2011).