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The common understanding in surface nuclear magnetic resonance (NMR) is that the excitation pulse should be kept much shorter than the NMR relaxation times for an effective excitation. We present analytic, numerical, and experimental evidence demonstrating that this need not be so, and surface NMR signals can be retrieved even for absurdly long excitation pulses. We solve the Bloch equations in the limit of infinitely long excitation and use this result to demonstrate that a measurable magnetization can be obtained with long excitation pulses. We perform numerical simulations of the Bloch equations incorporating effects of relaxation‐during‐pulse, and our results suggest that long excitation pulses can be used to increase the depth of investigation, but that the spatial resolution of long pulse excitation is low. Data collected in Kompedal, Denmark using up to 3 s long excitation pulses provide experimental proof for the feasibility of long pulse surface NMR. Plain Language Summary: Surface nuclear magnetic resonance (NMR) is the only non‐invasive geophysical method with a direct sensitivity to groundwater. A surface NMR measurement is carried out by pulsing a resonant current in a large coil laid out on the surface. This generates an electromagnetic field, which perturbs the nuclear spin of hydrogen nuclei in groundwater. The subsequent relaxation of the nuclear spins gives rise to a measurable signal with an amplitude proportional to the amount of groundwater and NMR relaxation times controlled by the host material of the water. The common understanding is that the excitation pulse should be much shorter than the NMR relaxation times for effective excitation. We present analytic, numerical, and experimental evidence demonstrating that this need not be so, and signals can be retrieved even for absurdly long excitation pulses. A numerical analysis of long pulse excitation suggests that this can be used to increase the depth of investigation. Experimental proof is given by a field data set where we retrieve NMR signals with a 200 ms relaxation time following excitation with a 3 s long pulse. Key Points: The influence of the nuclear magnetic resonance (NMR) excitation pulse duration in surface NMR is investigated in the long pulse limitEven if the NMR excitation pulse is much longer than the NMR relaxation times, surface NMR signals from groundwater can still be detectedThe depth of investigation in surface NMR measurements can be increased using long excitation pulses [ABSTRACT FROM AUTHOR]

Surface nuclear magnetic resonance (surface NMR) is a non-invasive method for the direct estimation of groundwater and aquifer properties. It measures nuclear magnetic signals generated by the surface wire loop, excited by radiofrequency pulses, and these signals are recorded using GMR QC software. After that, the pulses of the recorded surface NMR data (raw data) were analyzed, and the noise signals were filtered out to improve the quality of the surface NMR data. The pulse signals are merged into a single surface NMR signal to improve the data quality. The QT (pulse moment time) inversion model was used to estimate the hydraulic conductivity and water content below the groundwater table. The aquifer materials were classified based on the transverse relaxation time ( T 2 ∗ ), and results were compared with sieve analysis of soil samples. The transverse relaxation time (90–429 ms) indicated the presence of sand material, which complements laboratory results. The relative hydraulic conductivity of different types of soil was estimated by Kozeney's method. [ABSTRACT FROM AUTHOR]

A calibration procedure that fits the observed modeled data is used to determine the parameters of a hydrological model. As a result, the model parameters are highly uncertain. Estimation and the impact of uncertainty on model parameters have long been a source of debate. The bootstrap statistics method assesses uncertainty in surface nuclear magnetic resonance (surface NMR) water content and transverse relaxation time. The fundamental issue associated with the surface NMR data is that the quality of the surface NMR data is reduced in the presence of ambient electromagnetic and environmental noise. The bootstrap statistics is particularly well suited for estimating the uncertainty of the data set. We demonstrate that a bootstrap resampling of the observed synthetic data can provide an uncertainty estimate that closely fits the known uncertainty using synthetic forward modeled data with various noise levels, i.e., 5nV, 15nV, 30nV, and 50nV. The thickness of bootstrapped profile represents the uncertainty in the water content and relaxation time profiles. The thickness of the bootstrapped water content profile increases with an increase in noise level in the synthetic NMR data sets. Also, the thickness of the profiles increases along with the subsurface depth. Finally, we present seasonal field surface NMR data sets collected during the pre-monsoons and post-monsoon seasons under realistic ambient noise conditions. The surface NMR model was run for a 500–500 bootstrap to assess the pre-monsoon and post-monsoon uncertainty. This method is computationally extensive but straightforward to apply, and it provides valuable uncertainty estimates for both relaxation time and water content results for smooth-mono surface NMR models. [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: The surface nuclear magnetic resonance (NMR) signal can be difficult to isolate in the presence of a high‐amplitude noise source with an overlapping frequency, such as when a strong powerline harmonic sits atop the NMR signal. We demonstrate that the timing of surface NMR steady‐state sequences can be manipulated to alter the location of the NMR signal in the frequency domain, allowing one to separate the NMR signal from the overlapping strong noise source. Field results are given highlighting the feasibility of the technique and demonstrating that high fidelity NMR signals can be extracted even when they share a frequency with a higher amplitude powerline harmonic. Key Points: Steady‐state schemes allow users to control the nuclear magnetic resonance (NMR) signal's location in the spectraSteady‐state schemes can be exploited to increase separation between the NMR signal and nearby narrow‐band noise sourcesFrequency shifted steady‐state surface NMR data can be inverted reliably [ABSTRACT FROM AUTHOR]

The integration of non-invasive geophysical technologies has been popular in recent years for hydro-geophysical applications. Electrical resistivity tomography (ERT) and surface nuclear magnetic resonance (surface NMR) are geophysical methods for classifying subsurface soil media up to 100 m below the soil's surface. The main focus of the present study is to estimate the seasonal changes in the subsurface aquifer properties like water content and hydraulic conductivity using the combination of 2D/3D ERT and surface NMR methods, and these results were compared with the pulse moment time inversion (QTI) scheme. It was observed that small-scale variability in aquifer properties was found in the ERT and surface inversions. However, these models were developed for the field scale. Thus, small-scale variability can be neglected. During the post-monsoon and monsoon seasons, the size of low resistivity (4–14Ohm-m) and very low resistivity (23–33Ohm-m) zones are as shown in Fig. 5. Similarly, surface NMR measurements revealed a significant increase in the water content during these seasons. The chi-square value for the QTI scheme was 1.0672, which was quite near to 1. As a result, the QTI model is considered to be accurate for this study. The subsurface soil samples particle size distribution curves were studied, and soil components were classified using the transverse relaxation time. Thus, the combination of ERT and surface NMR approach promises to be a powerful tool for estimating subsurface characterization. [ABSTRACT FROM AUTHOR]

Groundwater is a critical freshwater source for billions of people (Klee, 2013), but resources are increasingly stressed by climate change, pollution, and overexploitation (Frappart & Ramillien, 2018, https://doi.org/10.3390/rs10060829). Locating groundwater sources and monitoring their sustainable use is a difficult task. One method that shows great promise is surface nuclear magnetic resonance (NMR), as it is the only technique capable of non‐invasive direct measurements of subsurface water content and pore‐space properties. Unfortunately, surface NMR often suffers from low‐amplitude signals that limit mapping speeds and may prohibit measurements in noisy environments. We demonstrate a steady‐state scheme for surface NMR, enabled by recent breakthroughs in transmitter capabilities and numerical modeling that delivers orders of magnitude signal enhancements. The new technique is a highly efficient measurement that is both narrowband and utilizes the full measurement interval in contrast to traditional approaches. Our results demonstrate that high‐fidelity groundwater measurements are now possible in hitherto inaccessible areas. Plain Language Summary: Surface nuclear magnetic resonance (NMR) is a non‐invasive technique that allows one to locate groundwater and quantify its abundance. The technique shows great promise to help enhance understanding of groundwater systems, but commonly suffers from low signal qualities due to low‐amplitude signals and high noise levels. To address the signal quality issues, a novel data acquisition strategy for surface NMR is presented, which involves measuring the signal produced by long pulse trains composed of identical repeated pulses. The proposed scheme's advantage over traditional workflows are an order of magnitude increase in stacking rates, and a dramatic reduction of noise bandwidths. The presented scheme shows great potential to expand the conditions where surface NMR can be employed. Key Points: Steady‐state surface nuclear magnetic resonance offers significant signal enhancements compared to traditional approachesSteady‐state processing enables a significant reduction of the noise bandwidth [ABSTRACT FROM AUTHOR]

We propose a simple and robust approach for investigating uncertainty in the results of inversion in geophysics. We apply this approach to inversion of Surface Nuclear Magnetic Resonance (SNMR) data, which is also known as Magnetic Resonance Sounding (MRS). Solution of this inverse problem is known to be non-unique. We inverse MRS data using the well-known Tikhonov regularization method, which provides an optimal solution as a trade-off between the stability and accuracy. Then, we perturb this model by random values and compute the fitting error for the perturbed models. The magnitude of these perturbations is limited by the uncertainty estimated with the singular value decomposition (SVD) and taking into account experimental errors. We use 10 6 perturbed models and show that the large majority of these models, which have all the water content within the variations given by the SVD estimate, do not fit data with an acceptable accuracy. Thus, we may limit the solution space by only the equivalent inverse models that fit data with the accuracy close to that of the initial inverse model. For representing inversion results, we use three equivalent solutions instead of the only one: the “best” solution given by the regularization or other inversion technic and the extreme variations of this solution corresponding to the equivalent models with the minimum and the maximum volume of water. For demonstrating our approach, we use synthetic data sets and experimental data acquired in the framework of investigation of a hard rock aquifer in the Ireland (County Donegal). [ABSTRACT FROM AUTHOR]

• The performance of modified empirical equations is significantly improved. • KC equation showed the highest correlation for both original and modified equations. • Estimated saturated K followed a similar pattern as surface NMR K. This study used eight empirical equations such as Kozeny-Carman (K-C), Terzaghi, Hazen, Slitcher, Kruger, Sauerbrei, NAVFACDM7, and Zamarin to estimate saturated hydraulic conductivity from soil particle size distribution and surface NMR porosity. The estimated empirical hydraulic conductivities were compared with the saturated surface nuclear magnetic resonance (surface NMR) hydraulic conductivity. It was found that most of the empirical equations showed poor correlation with the surface NMR hydraulic conductivity except Kozeny-Carman (KC), Hazen, and Zamarin equations. The value of the coefficient (β) of each equation is modified in such a way as to obtain a linear equation with the unit slope to improve the performance and accuracy of empirical equations. The modified Kozeny-Carman equation showed the maximum correlation R 2 = 0.904 , Pearson's r = 0.951 , and RMSE = 6.36 in comparison with other empirical equations. The NAVFACDM7 and the Terzaghi equations showed the highest underestimated hydraulic conductivity data (64 %) and overestimated hydraulic conductivity data (38 %) ; however, the Zamarin equation showed the highest overlapped hydraulic conductivity data (44 %) , respectively, with the 1:1 line. [ABSTRACT FROM AUTHOR]

Dynamic nuclear polarization (DNP) is a method for enhancing nuclear magnetic resonance (NMR) signals that has many potential applications in chemistry and medicine. Traditionally, DNP signal enhancement is achieved through the use of exogenous radicals mixed in a solution with the molecules of interest. Here we show that proton DNP signal enhancements can be obtained for solid samples without the use of solvent and exogenous radicals. Radicals are generated primarily on the surface of a solid sample using electrical discharges. These radicals are found suitable for DNP. They are stable under moderate vacuum conditions, yet readily annihilate upon compound dissolution or air exposure. This feature makes them attractive for use in medical applications, where the current variety of radicals used for DNP faces regulatory problems. In addition, this solvent-free method may be found useful for analytical NMR of solid samples which cannot tolerate solvents, such as certain pharmaceutical products. [ABSTRACT FROM AUTHOR]

The chemisorption and breakdown of methionine (Met) adsorbed on Pd/γ-Al 2 O 3 catalysts were investigated by solid-state NMR. 13 C-enriched Met (ca. 0.4 mg) impregnated onto γ-Al 2 O 3 or Pd/γ-Al 2 O 3 gives NMR spectra with characteristic features of binding to γ-Al 2 O 3 , to Pd nanoparticles, and oxidative or reductive breakdown of Met. The SCH 3 groups of Met showed characteristic changes in chemical shift on γ-Al 2 O 3 (13 ppm) vs. Pd (19 ppm), providing strong evidence for preferential binding to Pd, while the NC carbon generates a small resonance at 96 ppm assigned to a distinct nonprotonated species bound to O or Pd. Additionally, NMR shows that the SCH 3 groups of Met are mobile on γ-Al 2 O 3 but immobilized by binding to Pd particles; on small Pd particles (ca. 4 nm), the NCH groups undergo large-amplitude motions. In a reducing environment, Met breaks down by C–S bond cleavage followed by formation of C 2 –C 4 organic acids. The SCH 3 signal shifts to 22 ppm, which is likely the signature of the principal species responsible for strong catalyst inhibition. These experiments demonstrate that solid-state magic-angle spinning NMR of 13 C-enriched Met can be a sensitive probe to investigate catalyst surfaces and characterize catalyst inhibition both before reaction and postmortem. [ABSTRACT FROM AUTHOR]

A method for estimating uncertainty in surface nuclear magnetic resonance (NMR) water content and relaxation times utilizing bootstrapping statistics is presented. Bootstrapping is particularly well suited for assigning uncertainty to the surface NMR data set due to the primary factor that degrades surface NMR data quality: ambient electromagnetic noise. We use synthetic forward modeled data with various noise levels applied (the “known uncertainty”), and then demonstrate that a bootstrap resampling of the observed synthetic data can produce an uncertainty estimate that closely represents the “known uncertainty”. Finally, we present two field data sets collected under different magnitude ambient noise levels as examples illustrating the result of this approach under realistic noise conditions. This approach for estimating uncertainty is computationally intensive, but straightforward to implement and produces useful uncertainty estimates on both water content and relaxation time results for smooth surface NMR sounding models. [ABSTRACT FROM AUTHOR]

The technique of surface NMR has been applied to image 1D, 2D and recently 3D subsurface structures. Although limited resolution is reported for imaging deep 3D structures using a coincident loop configuration, high resolution is obtained for shallow 2D structures by including separated loop configurations. We adapt the concept of separated transmitter and receiver loops to obtain increasing resolutions for imaging 3D shallow structures. We present a numerically efficient approach to calculate the 3D kernel with sufficient accuracy and a small number of elements. Using synthetic data, we show that including separated loop layouts enhances the 3D image reconstruction. To evaluate our 3D inversion approach, a field campaign including surface NMR with various layouts and ground penetration radar (GPR) measurements was conducted on top of a frozen artificial barrier lake in the Harz Mountains (Germany, Lower Saxony) with a well known geometry. We show that the results obtained from measurements using the coincident loop layout give a rough approximation of the lake's bathymetry, and including separated loop layouts provides a more detailed view into the subsurface. In particular, the obtained image matches not only the known water content of 100%, but the geometry known from construction plans and estimated from GPR profiles. In addition to the 3D assessment, a 2D profile is extracted from the 3D dataset to demonstrate the need for 3D inversion. [ABSTRACT FROM AUTHOR]

Abstract: Surface nuclear magnetic resonance (surface NMR) is a geophysical technique used in the exploration of shallow aquifers. It is based on measuring the NMR response of water molecules to excitation by electromagnetic pulses. By increasing the moment of applied pulses, successively deeper regions of an aquifer can be probed. The longitudinal relaxation time T 1, determined from the NMR experiment, depends on pore size and can be potentially used to estimate hydraulic conductivity. A novel scheme was recently proposed that was shown theoretically to be more reliable for acquiring surface-NMR T 1 data than traditional acquisition. In this proof-of-concept study we provide the first empirical evidence for the superiority of the novel scheme. We chose a survey site close to Skive, Denmark, where proximate boreholes indicate a homogeneous sandy aquifer in the top 30m. The homogeneous composition implies that the distribution of pore sizes does not vary significantly across the formation. Because pore size is reflected by the T 1 relaxation time, we therefore assume that the homogeneous aquifer can be characterized by a single T 1 independent of the applied pulse moment (i.e., sampled depth region)—this is the benchmark condition we tested with our surface-NMR measurements. We collected surface-NMR T 1 data employing the traditional as well as the novel acquisition scheme at various pulse moments. For each pulse moment we infer a T 1 relaxation time based on extensively sampled data (14 delay-time data points). The T 1 relaxation times obtained using the novel scheme show a constant value of about 820ms (±38ms) for all pulse moments. In contrast, the T 1 relaxation times determined using the traditional scheme vary significantly between 530 and 750ms with pulse moment, which in an inversion would result in a spatial variation of T 1 across the aquifer. The results based on the novel scheme are consistent with a homogeneous aquifer, which we expect based on the borehole information, whereas the variation of T 1 obtained by the traditional scheme could be misinterpreted as a variation of pore size or hydraulic conductivity. [Copyright &y& Elsevier]

Abstract: Multi-channel surface nuclear magnetic resonance (NMR) instrumentation and software, developed in the United States, has been applied to investigate 1D and 2D hydrology at various locations in the Western US. The GeoMRI instrument offers several practical improvements over the previous state of the art in surface NMR instrumentation, including a multi-channel transmit/receive capability, a significantly shorter measurement dead-time of 10 ms, and an ultra-low receiver input noise density of less than 0.4 nV/sqrt (Hz). Two multi-channel NMR processing techniques, reference coil-based noise cancellation and integrated FID imaging, are shown to increase effective signal to noise ratios by an order of magnitude or more. These effective SNR gains enable multi-coil surface NMR to produce useful and reliable images when the post-averaged SNR is less than 1. We also suggest an alternate approach to imaging, in which NMR signals are initially isolated in the space domain, and then NMR parameter estimation is applied in the time domain. Experimental results are presented for recent surface NMR groundwater investigations conducted in Nebraska and Texas, USA. [Copyright &y& Elsevier]

A new portable nuclear magnetic resonance (NMR) device allows in situ non-invasive investigation of paper in order to examine some aspects of the microscopic healthy state of documents of historical and artistic interest. The apparatus has a NMR surface probe, which permits to perform most of the NMR relaxometric measurements on objects of almost every size and shape. It uses non-ionizing radio frequency electromagnetic waves and is easily transportable without hazard for people or environment. Some results obtained with this device on the pages of the Codex Major, a manuscript musical anthology that belongs to the Collectio Altaempsiana (1600–1610) of Palazzo Altaemps in Rome, are here presented. The NMR results provide indications about the spread of the deterioration process of the paper and of the corrosion effect caused by the iron-gall ink. [Copyright &y& Elsevier]

The Magnetic Resonance Sounding (MRS) method is based on the resonance behaviour of proton magnetic moments in the geomagnetic field. The main distinction between MRS and other geophysical methods is that it measures the magnetic resonance signal directly from groundwater molecules, making it a selective tool sensitive to groundwater. As the signal generated by the protons is very small, the method is also sensitive to electromagnetic interference (noise) and this is one of the major limitations for practical application. The frequency of the magnetic resonance signal (the Larmor frequency) is directly proportional to the magnitude of the geomagnetic field and varies between 800 and 2800 Hz around the globe. Whilst natural noise within this frequency range is generally not very large (excepting magnetic storms or other temporary disturbances), the level of cultural noise (electrical power lines, generators, etc.) may be very high. In order to improve performance, three existing filtering techniques were adapted to processing MRS measurements: block subtraction, sinusoid subtraction and notch filtering. The first two are subtraction techniques capable of suppressing stationary power-line noise without distorting or attenuating the signal of interest, both involve subtracting an estimate of the harmonic component but differ in the way the component is estimated. The block subtraction method consists of ascertaining the power-line noise (or “noise block”) from a record of the noise alone, and then subtracting this block from a record containing both the noise and the signal. The sinusoid subtraction method is based on the calculation of the amplitude, frequency and phase of power-line harmonics using noise records. The notch filtering method does not require knowledge of the power-line harmonic parameters but it may cause distortion of the measured signal. During the study, it was found that, in the investigated frequency range, the electromagnetic noise produced by electrical power lines was much less stable and regular than expected. The proportion of 50 Hz harmonics (regular part) in the noise energy is site-dependent and may vary between 20% and 50%. Whilst the power-line harmonics are seen clearly on the noise spectra, the amplitude and frequency of each harmonic may vary significantly from one record to another. Under these conditions, any block subtraction scheme based on a high noise regularity cannot be used systematically. The sinusoid subtraction is generally more efficient than the block subtraction and its application allows noise reduction by a factor of up to nearly 5. The notch filtering technique was studied further using a synthetic signal mixed with real noise and the results show that the noise can be reduced by factors of 2–10. The efficiency of the investigated filtering techniques is site-dependent. Three important factors define how successfully noise can be filtered from the signal record: the difference between the Larmor frequency and the nearest power-line harmonic frequency; the relaxation time of the magnetic resonance signal; and the proportion of the regular part of the noise spectrum. In most cases though, the improvement achieved in the critical signal-to-noise ratio (S/N) (5- to 8-fold on average) enables MRS application to be extended towards more noisy areas. The efficiency of the notch filtering technique applied to MRS measurements is demonstrated by a field example from France. [Copyright &y& Elsevier]

Motivated by the recent application of the Earth-field nuclear magnetic resonance (NMR) technique to the detection and mapping of subsurface groundwater (to depths of 100 m or so), and making use of a recently developed theory of the method, we consider in detail the resulting inverse problem, namely the inference of the subsurface water distribution from a given sequence of NMR voltage measurements. We consider the simplest case of horizontally stratified water distributions in a horizontally stratified conducting Earth. Inversion methods based both on the singular value decomposition (SVD) and Monte Carlo are used and compared. The effects of random measurement errors and of systematic errors in the assumed subsurface conductivity structure are studied. It is found that an incorrectly modeled highly conducting layer leads to a “screening effect” in which the water content of layers lying below it is severely underestimated. We investigate also the ability of different source-receiver loop geometries to provide complementary information that may improve a combined inversion. Finally, inversion of experimental data from Cherry Creek, CO, USA is performed. Since only the absolute magnitude of the NMR voltage is measured accurately, a nonlinear Monte Carlo inversion is performed. [Copyright &y& Elsevier]

The proton Magnetic Resonance Sounding (MRS) is a geophysical technique specially designed for hydrogeological applications. It is based on the principle of Nuclear Magnetic Resonance (NMR) and allows the non-invasive detection of free water in the subsurface.As with many other geophysical methods, MRS is site-dependent. Modeling results show that MRS performance depends on the magnitude of the natural geomagnetic field, the electrical conductivity of rocks, the electromagnetic noise and other factors. For example, the maximum depth of groundwater detection for currently available equipment can vary from 45 to 170 m depending on measurement conditions, although an average depth of investigation is generally considered to be about 100 m. The processing of MRS data can provide the depth, thickness and water content of aquifers.Based on the water content and the relaxation times T1 and T2* provided by MRS, in association with calibration using borehole pumping test data, it is possible to estimate the aquifer''s hydrodynamic properties, namely permeability, transmissivity, and specific yield. In this aim, experience gained through NMR logging has been applied to MRS data interpretation and a comparison between the results of borehole pumping tests and those of MRS experiments reveals a good correlation.An example of an MRS survey in Saudi Arabia is presented. The study area is some 1.3 km2 and underlain by an aquifer composed of fractured diorite. The results of 7 borehole pumping tests and 13 MRS measurements show good agreement. [Copyright &y& Elsevier]

The Surface Nuclear Magnetic Resonance (SNMR) method is a fairly new technique in geophysics to assess ground water, i.e. existence, amount and productibility by measurements at the surface. The NMR technique used in medicine, physics and lately in borehole geophysics was adopted for surface measurements in the early eighties, and commercial equipment for measurements has been available since the mid nineties. The SNMR method has been tested at sites in Northern Germany with Quaternary sand and clay layers, to examine the suitability of this new method for groundwater exploration and environmental investigations. More information is obtained by SNMR, particularly with respect to aquifer parameters, than with other geophysical techniques. SNMR measurements were carried out at three borehole locations, together with 2D and 1D direct current geoelectrics and well logging (induction log, gamma-ray log and pulsed neutron-gamma log). Permeabilities were calculated from the grain-size distributions of core material determined in the laboratory. It is demonstrated that the SNMR method is able to detect groundwater and the results are in good agreement with other geophysical and hydrogeological data. Using the SNMR method, the water content of the unsaturated and saturated zones (i.e. porosity of an aquifer) can be reliably determined. This information and resistivity data permit in-situ determination of other aquifer parameters. Comparison of the SNMR results with borehole data clearly shows that the water content determined by SNMR is the free or mobile water in the pores. The permeabilities estimated from the SNMR decay times are similar to those derived from sieve analysis of core material. Thus, the combination of SNMR with geoelectric methods promises to be a powerful tool for studying aquifer properties.