Steady‐State Surface NMR for Mapping of Groundwater

Grombacher, Denys; Liu, Lichao; Griffiths, Matthew P.; Vang, Mathias; Larsen, Jakob Juul

doi:10.1029/2021gl095381

Cited by 10 publications

(2 citation statements)

References 34 publications

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“…In this work we focus on a recently developed steady‐state approach to surface NMR acquisition, where the NMR signal is collected during a train of identical pulses each separated by a fixed delay time (Carr, 1958; Grombacher et al., 2021). This approach has been demonstrated to offer significant signal‐to‐noise ratio enhancements over traditional FID approaches.…”

Section: Introductionmentioning

confidence: 99%

“…Several processing workflows have been explicitly tailored to address co-frequency issues, focused on either modeling and removing this signal (Liu et al, 2017;Wang et al, 2018) or on exploiting spectral properties of data windows (Grombacher, Kass, et al, 2020;Grombacher, Liu, et al, 2020). Each of these schemes have been developed in the context of free-induction decay (FID) acquisition strategies and focus on denoising the time-domain NMR signal.In this work we focus on a recently developed steady-state approach to surface NMR acquisition, where the NMR signal is collected during a train of identical pulses each separated by a fixed delay time (Carr, 1958;Grombacher et al, 2021). This approach has been demonstrated to offer significant signal-to-noise ratio enhancements over traditional FID approaches.…”

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confidence: 99%

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Frequency Shifting Steady‐State Surface NMR Signals to Avoid Problematic Narrowband‐Noise Sources

Grombacher

Griffiths

Liu

et al. 2022

Geophysical Research Letters

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Recent developments in surface nuclear magnetic resonance (NMR) based on steady‐state sequences show great enhancements in signal quality and mapping speeds. We demonstrate how manipulating the timing and phase of these sequences can shift the NMR signal away from problematic narrow‐band noise sources, for example, co‐frequency powerline harmonics, or shift narrowband noise sources away from the NMR signal. The spectral separation of the NMR signal from co‐frequency noise sources enables production of high‐quality data under one of the most challenging noise scenarios in surface NMR. We demonstrate the feasibility with surface NMR measurements at a site where the Larmor frequency coincides with a powerline harmonic. We separate the NMR signal and powerline noise by up to 5 Hz and obtain high‐quality data, which are readily inverted. The approach is straightforward to implement, well suited for field processing, and shows great potential to expand the range of conditions allowing surface NMR measurements.

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Section: Introductionmentioning

confidence: 99%

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confidence: 99%

Frequency Shifting Steady‐State Surface NMR Signals to Avoid Problematic Narrowband‐Noise Sources

Grombacher

Griffiths

Liu

et al. 2022

Geophysical Research Letters

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Bloch–Siegert Effect for Surface Nuclear Magnetic Resonance Sounding Experiments in the Unsaturated Zone

2023

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The Bloch–Siegert effect is relevant for NMR experiments where components of the excitation pulse other than the circularly polarized component have an influence on the evolution of the magnetization of the spin system under consideration. For linearly polarized excitation fields this happens at amplitudes higher than roughly one tenth of the magnitude of the static magnetic field. Since surface nuclear magnetic resonance (SNMR) experiments, also called magnetic-resonance-soundings (MRS), are conducted in the relatively low local field of the earth, the Bloch–Siegert effect can quickly become relevant. This is especially the case for SNMR experiments in the unsaturated zone, where due to short relaxation times fast pulses of high intensity must be used. To describe the Bloch–Siegert effect, we use the average Hamiltonian approximation obtained by the Magnus expansion of up to fifth order, as well as the solution of the Bloch equations. The results of these approximations are tested against the Bloch simulations and it is shown that they are only valid for limited ranges of the excitation field amplitude. The influence of the Bloch–Siegert effect on sensitivity kernels is described and verified with experimental data obtained with a small scale SNMR sensor on water containers.

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Remote sensing and hydrogeophysics give a new impetus to integrated hydrological models: A review

Lubczynski,

Leblanc,

Batelaan

2024

Journal of Hydrology

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Steady‐State Surface NMR for Mapping of Groundwater

Abstract: Isolating the sensitivity of geophysical measurements to water at depth is a difficult task. Commonly employed electromagnetic (

Cited by 10 publications

References 34 publications

Frequency Shifting Steady‐State Surface NMR Signals to Avoid Problematic Narrowband‐Noise Sources

Frequency Shifting Steady‐State Surface NMR Signals to Avoid Problematic Narrowband‐Noise Sources

Bloch–Siegert Effect for Surface Nuclear Magnetic Resonance Sounding Experiments in the Unsaturated Zone

Remote sensing and hydrogeophysics give a new impetus to integrated hydrological models: A review

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