One-dimensional hydrogeophysical forward model in surface nuclear magnetic resonance (SNMR) computations
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One-dimensional hydrogeophysical forward model in surface nuclear magnetic resonance (SNMR) computations M. Gupta
Received: 5 April 2013 / Accepted: 4 August 2013 / Published online: 20 September 2013 © Akadémiai Kiadó, Budapest, Hungary 2013
Abstract Surface nuclear magnetic resonance (SNMR) technique is a novel method for the detection of groundwater and characterization of aquifers. A three-layered Earth model with a conductive-sandwiched bed (aquifer) within resistive layers has been used for estimating the SNMR signal. The magnetic field expressions have been developed for a three-layered medium due to an oscillating magnetic dipole kept above air-Earth interface. It involved independent theoretical formulation of the forward problem. For a given depth-wise distribution of water content confined to a three-layered Earth medium, the NMR signal response has been sought. The forward model is tested in a typical H-type Earth section and the computed NMR signal clearly identified the groundwater presence in the sandwiched layer. The computation of magnetic field expressions for a simple three-layered Earth sets the ground for computation and detection of more complex magnetic fields for multi-layered Earth containing materials of different resistivity. With global need for sustainable requirement of groundwater usage and distribution for various purposes, SNMR technique is slated to provide a means of faster and cheaper hydrological solutions. Keywords Forward modelling · Groundwater · Hydrogeophysics · SNMR · Three-layered Earth
1 Introduction Out of all the water found on the planet Earth, around only 1.7 % is groundwater, which is the primary source of drinking water (Gleick 1996). With increasing demand of water for
M. Gupta Department of Earth Sciences, Indian Institute of Technology, Roorkee 247 667, Uttarakhand, India Present address: M. Gupta ( ) Department of Environment and Geography, Clayton H. Riddell Faculty of Environment, Earth, and Resources, University of Manitoba, Winnipeg R3T 2N2, Manitoba, Canada e-mail: [email protected]
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Acta Geod Geophys (2013) 48:363–376
drinking, irrigation, and industrial use, developments of non-invasive new tools and techniques are needed for groundwater exploration and aquifer characterization. Surface nuclear magnetic resonance (SNMR) is a novel technique for the detection of bound and free groundwater (Legchenko et al. 2002). The application of SNMR technique for groundwater (also hydrocarbon) exploration in hydrogeophysics has been studied mainly since 1980s. Although, Varian (1962) gave the first idea for groundwater detection using SNMR method, significant advances were made only after the development of the equipment (Semenov et al. 1982). The principle of NMR technique is based on the fact that protons in the water molecules get excited if an external magnetic field is applied (Legchenko and Valla 2002). The magnetic field is created with the help of an induction coil at the air-Earth interface. The induced current in the coil carries the same
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