Comparison and optimal parameter settings of reference-based harmonic noise cancellation in time and frequency domains for surface-NMR

The technique of surface nuclear magnetic resonance (surface-NMR) provides information on porosity and hydraulic conductivity that is highly valuable in a hydrogeological context. However, the applicability of surface-NMR is often limited due to a bad signal-to-noise ratio. In this paper we provide a detailed insight into the technique of harmonic noise cancellation based on remote references to improve the signal-to-noise ratio. We give numerous synthetic examples to study the influence of various parameters such as optimal filter length for time-domain approaches or the necessary record length for frequency-domain approaches, all of which evaluated for different types of noise conditions. We show that the frequency-domain approach is superior to time-domain approaches. We demonstrate that the parameter settings in the frequency domain and the decision whether or not to use separated noise measurement depend on the actual noise properties, i.e., frequency content or stability with time. We underline our results using two field examples.