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

Even though 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 approach, we developed an own frequency domain code beside the existing time domain code (Müller-Petke and Yaramanci, 2011). The algorithms were tested using synthetic examples and a field examples. It shows that with increasing complexity of the noise the frequency domain approach provides better results compared to the time domain for the synthetic examples. Concerning the field data both approaches are equivalent. We found that using the multi-channel reference the signal enhancement is improved.