A NOVEL NMR INSTRUMENT FOR CHARACTERIZATION OF SOIL MOISTURE

PreviousNext You have accessSymposium on the Application of Geophysics to Engineering and Environmental Problems 2013A NOVEL NMR INSTRUMENT FOR CHARACTERIZATION OF SOIL MOISTUREAuthors: David WalshElliot GrunewaldHong ZhangDavid Walsh Vista Clara Inc.Search for more papers by this author, Elliot Grunewald Vista Clara Inc.Search for more papers by this author, and Hong Zhang Vista Clara Inc.Search for more papers by this authorhttps://doi.org/10.4133/sageep2013-148.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract We have developed a novel NMR instrument that provides direct measurement and characterization of soil moisture in the shallow subsurface. The quantity and distribution of water in the upper meter of the subsurface is of critical importance for a wide range of geotechnical, agricultural, and environmental applications. Existing technologies for measuring soil moisture are limited. Electrical and electromagnetic methods rely heavily upon uncertain and lithologically-variable rock physics transforms to estimate hydrologic properties. Neutron-based measurements provide more accurate results, but still require calibration, and permitting for radioactive neutron sources is increasingly time- and cost-prohibitive. The advantage of NMR measurements is that they yield direct detection and quantification of water content, and provide further detailed information about the pore space via the NMR relaxation times. The instrument we have developed performs non-invasive measurements in the presence of a static magnetic field gradient. By performing measurements over a range of frequency in the low RF band (40 kHz − 500 kHz), the tool provides profiling capabilities to determine the NMR response at variable depth levels. This design also minimizes diffusion and remnant magnetization artifacts that can otherwise contaminate the NMR measurement and interpretation. The current design has a maximum investigation depth of 30 cm but larger designs may profile to 1 m depth. A CPMG measurement sequence is used to determine the T2 distribution at each depth. An echo-time of 1 ms or less enables detection of very short signals, dominant in the unsaturated zone. Typical point measurements can be acquired in 3 minutes or less. Conventional interpretation of the T2 distribution provides direct quantification of water content, estimation of bound versus mobile water content – and in saturated media, pore size and permeability. It is anticipated that additional geotechnical parameters and agricultural parameters of value may be determined from the measured NMR response. We present the technical aspects of the instrumentation and a collection of field experiments that demonstrate the tool capabilities over a range of environmental conditions. Permalink: https://doi.org/10.4133/sageep2013-148.1FiguresReferencesRelatedDetails Symposium on the Application of Geophysics to Engineering and Environmental Problems 2013ISSN (online):1554-8015Copyright: 2013 Pages: 821 publication data© 2013 Published in electronic format with permission by the Environment and Engineering Geophysical SocietyPublisher:Environmental & Engineering Geophysical Society HistoryPublished: 28 May 2013 CITATION INFORMATION David Walsh, Elliot Grunewald, and Hong Zhang, (2013), "A NOVEL NMR INSTRUMENT FOR CHARACTERIZATION OF SOIL MOISTURE," Symposium on the Application of Geophysics to Engineering and Environmental Problems Proceedings : 698-698. https://doi.org/10.4133/sageep2013-148.1 Plain-Language Summary PDF DownloadLoading ...