Bio

I am working with my research group to find innovative ways of using geophysical methods to understand the hydrologic processes occurring in the top kilometer of Earth. In 1985 I coined a term to describe this work, “hydrogeophysics” - a sub-discipline that has grown dramatically over the past 30 years. A current focus of my group is the integration of geophysical imaging with remote sensing data for the evaluation and management of groundwater resources; this research is being done in partnerships with groundwater managers in the western U.S. Using laboratory and field experiments, and computer modeling, we are developing new methods for acquiring, processing, and interpreting geophysical data; and discovering new links between our geophysical images, and hydrologic properties and processes

Academic Appointments

Administrative Appointments

  • Senior Fellow Stanford Institute for the Environment, Stanford University (2005 - Present)
  • Professor Geophysics, Stanford University (2000 - Present)
  • Professor, University of British Columbia (1998 - 2000)
  • Associate Professor, University of British Columbia (1993 - 1998)
  • Assistant Professor, University of British Columbia (1988 - 1993)
  • NSERC University Research Fellow, University of British Columbia (1987 - 1988)
  • Acting Assistant Professor Geophysics, Stanford University (1984 - 1987)

Honors & Awards

  • Gold Medal in Geological Sciences, Queen's University (1976)
  • NSERC University Research Fellowship, Natural Sciences and Engineering Resources Council (1987)
  • Distinguished Speaker Award, Society of Professional Well Log Analysts (1991)
  • Best Paper Award, MGLS/KEGS Symposium, "Borehole Geophysics for Minerals, Geotechnical...", Toronto, MGLS/KEGS (1991)
  • Teaching Excellence Award, University of British Columbia (1992)
  • Distinguished Lecturer, Canadian Geophysical Union (1995)
  • Best Paper Award Honorable Mention, Society of Exploration Geophysicists (1996)
  • Killam Research Prize for research excellence, University of British Columbia (1996)
  • Charles McDowell Medal, for excellence in pure and applied research, University of British Columbia (1996)
  • Distinguished Lecturer, Society of Exploration Geophysicists (1998)
  • Frank Frischknecht Award, Society of Exploration Geophysicists Near Surface Section (2002)
  • Life Membership Award, Society of Exploration Geophysicists (2009)
  • Honorary Life Membership Award, Society of Exploration Geophysicists, Near-Surface Geophysics Section (2012)

Boards, Advisory Committees, Professional Organizations

  • Invited Conference Keynote Speaker: Measuring K, Monitoring Head: Addressing a Growing Need for Characterization and Monitoring of Groundwater Aquifers, Novel Methods for Subsurface Characterization and Monitoring, Lawrence Kansas (2015 - 2015)
  • Invited Conference Keynote: Advancing Geophysical Methods for Groundwater Evaluation and Management, Australian Society of Exploration Geophysicists (2015 - 2015)
  • Organizing Committee, Workshop on Magnetic Resonance of the Subsurface, Aarhus, Denmark, June 2015 (2014 - 2015)
  • Classes Without Quizzes, Stanford Reunion Weekend: Our Freshwater Future, Stanford Alumni Association (2014 - 2014)
  • Invited Presentation: Electrical Resistivity Imaging of Saltwater and Freshwater Along the Coast of Monterey Bay, American Geophysical Union (2014 - 2014)
  • Presentations at Stanford Connects, Monterey, CA, Stanford Alumni Association (2014 - 2014)
  • Scientific Advisor, HyGEM Project: Integrating geophysics, geology, and hydrology for improved groundwater and environmental management, Aarhus University (2013 - Present)
  • Member, Undergraduate Advisory Committee, Stanford University (2013 - 2015)
  • Special Co-Editor for issue on Magnetic Resonance of the Subsurface, Near-Surface Geophysics Journal (2012 - 2014)
  • Invited Presentation: The Center for Groundwater Evaluation and Management - Developing Partnerships, Society of Exploration Geophysicists Annual Convention (2012 - 2012)
  • Member (elected) Faculty Senate, Stanford University (2011 - 2013)
  • Chair (elected) Faculty Senate, Stanford University (2011 - 2012)
  • Chair, Organizing Committee, SEG-AGU Hydrogeophysics Workshop, Boise ID, July, Society of Economic Geologists and American Geophysical Union (2011 - 2012)
  • Member, Undergraduate Advisory Committee, Stanford University (2011 - 2012)
  • Co-organizer, Session Chair, The Use of Geophysical Methods for Evidence-Based Groundwater Management, Charleston, S.C., April 10-14, Symposium for the Application of Geophysics to Environmental and Engineering Problems (2011 - 2011)
  • Invited Presentation, Annual Convention, Nuclear Magnetic Resonance: From Pore-Scale Physics to Field-Scale Hydrogeophysics, Society of Exploration Geophysicists (2011 - 2011)
  • Invited Presentation: The Sensitivity of Dielectric and NMR Measurements to Sorption at the Solid/Water Interface, American Geophysical Union: (2011 - 2011)
  • Member, DARE Fellowship Advisory Committee, Office of Graduate Education, Stanford University (2011 - 2011)
  • Chair, Dept of Energy Earth Sciences Council, Stanford University (2010 - 2012)
  • Earth Sciences Council, School of Earth Sciences, Stanford University (2010 - 2012)
  • Seminar Co-ordinator, Department of Geophysics, Stanford University (2010 - 2011)
  • Coursework Advisory Committee, Stanford University (2009 - 2011)
  • Invited Presentation & Panel Discussion: SEG Forum, Managing Our Groundwater Resources, Society of Exploration Geophysicists (2009 - 2009)
  • Invited Presentation: The Use Of Geophysical Methods To Characterize Hydrogeologic Systems Across Multiple Scales, American Geophysical Union Joint Assembly (2009 - 2009)
  • Invited Presentation: The Use of Geophysical Methods for Groundwater Evaluation and Management, University of Texas at Austin, Jackson School of Geosciences (2009 - 2009)
  • The Use of Geophysical Methods for Hydrogeologic Applications, B.C. Geophysical Society (2009 - 2009)
  • Faculty Lead, Shared Field Measurement Facility, School of Earth Sciences, Stanford University (2008 - 2011)
  • Future Focus Task Force Member, American Geophysical Union (2008 - 2009)
  • Co-Organizer (with P Kitanidis): Uncommon Dialogue: Comprehensive Studies of Aquifer Depletion and Desalinization, Woods Institute for the Environment, Dec. 4-5, Stanford University (2008 - 2008)
  • Invited Presentation: I-Earth – Introduction to Planet Earth, Boston, MA, American Association for the Advancement of Science (2008 - 2008)
  • Faculty Lead (with R. Luthy), Freshwater Initiative, Woods Institute for the Environment, Stanford University (2007 - 2009)
  • Co-Organizer (with R. Luthy), The Water Seminar, Woods Institute for the Environment, Stanford University (2007 - 2008)
  • Invited Keynote Speaker: The Development of Geophysical Methods for Hydrogeologic Applications, Bicentennial Conference, London, England, 10-12 September, The Geological Society of London (2007 - 2007)
  • Invited Presentation, Annual Meeting: Integration of Remote Sensing, Hydrologic, and Geophysical Data to Determine the Time-Varying Behavior of a Hydrogeologic System, Geological Society of America (2007 - 2007)
  • Invited Presentation: Workshop on Three-dimensional Geologic Mapping for Groundwater Applications, Annual Meeting, Denver, Colorado: The Use of Ground-Penetrating Radar Data in the Development of Facies-Based Hydrogeologic Models, Geological Society of America (2007 - 2007)
  • Speaker, Arthur Walker Seminar Series (Spring), Stanford University (2007 - 2007)
  • Faculty Lead, Introduction to Planet Earth, Stanford-wide educational initiative, Stanford University (2006 - Present)
  • Steering Committee, Stanford K-12 Initiative, Stanford University (2006 - 2010)
  • Co-Organizer Research Workshop on Hydrogeophysics, July, Vancouver Canada, Hydrogeophysics Research Group (2006 - 2006)
  • Co-organizer, Session Chair, Watershed Geophysics, Seattle, WA, April 2-6, Symposium for the Application of Geophysics to Environmental and Engineering Problems (2006 - 2006)
  • Invited Lecture, The Support Volume of Geophysical Measurement: How and Why to Define It, American Geophysical Union: (2006 - 2006)
  • Invited Union Lecture, Near-Surface Geophysics: Advancing Earth Sciences Through Advances in Imaging, American Geophysical Union: (2006 - 2006)
  • Invited lecture, Annual Meeting, Philadelphia: Characterizing Hydrogeologic Heterogeneity Using Geophysical Methods: From Laboratory-Scale Observations to Field-Scale Applications, Geological Society of America (2006 - 2006)
  • Invited lecture, Near-Surface Geophysics: Electromagnetic Experiments in the Laboratory and Into the Field, U.C. Berkeley (2006 - 2006)
  • Invited presentation, Ground Water Expo, Las Vegas NV, Dec 5-8, Hydrogeophysics Overview: The Use of Geophysics in Groundwater Evaluation and Management, National Ground Water Association (2006 - 2006)
  • Chair, Department of Geophysics, Stanford University (2005 - 2008)
  • Chairperson, Near-Surface Geophysics Focus Group, American Geophysical Union (2005 - 2008)
  • Faculty Lead, Stanford Syllabus Project, Stanford University (2005 - 2008)
  • SAGE ((Summer) | of Applied Geophysical Experience) Advisory Committee, Summer of Applied Geophysical Experience (SAGE) (2005 - 2007)
  • Invited Lecture: An Emerging Role for Geophysics in the Evaluation and Management of Water Resources, Sandia National Lab Geosciences Distinguished Lecture Series (2005 - 2005)
  • Invited lecture, An Emerging Role for Geophysics in Watershed Scale Hydrology, American Geophysical Union: (2005 - 2005)
  • Invited lecture, Dept of Earth, Atmosphere and Planetary Sciences: Using Ground Penetrating Radar to Quantify Spatial Variation in Water Content, MIT (2005 - 2005)
  • Invited lecture: The Use of Geophysical Methods for Quantifying the Spatial Distribution in Water Content, Oregon State University, Corvallis (2005 - 2005)
  • Steering Committee of the Instrumentation Working Group of the future National Center for Hydrologic Synthesis (NCHS), National Center for Hydrologic Synthesis (NCHS) (2005 - 2005)
  • Member, University Budget Group, Stanford University (2004 - Present)
  • Area 1 (Intro to the Humanities) Governance Board member, Stanford University (2004 - 2006)
  • Chair, University Committee on Undergraduate Standards and Policy (C-USP), Stanford University (2004 - 2006)
  • Associate Editor, Water Resources Research (2004 - 2005)
  • Undergraduate Advisory Committee Member, Stanford University (2004 - 2005)
  • Academic Review Committee, Hydrology and Water Resources, University of Arizona (2004 - 2004)
  • Invited lecture: Groundwater Geophysics - Finding New Ways to See Into the Earth., Engineers without Frontiers (2004 - 2004)
  • Member, Geophysics Dept. Review Committee, Lawrence Berkeley National Lab (2004 - 2004)
  • Director, Hydrologic Measurement Facility for Geophysics, NSF-supported Consortium of Universities for the Advancement of Hydrologic Sciences, National Science Foundation (2003 - 2008)
  • Chair, School of Earth Sciences Sub-Committee on Academic Programs, Stanford University (2003 - 2004)
  • Invited Plenary Speaker: Inland Northwest Research Alliance Subsurface Science Symposium, Salt Lake City, Utah: Geophysical Images of the Near-Surface -- What are We Really Seeing?, Inland Northwest Research Alliance (2003 - 2003)
  • Invited lecture: The Use of Ground Penetrating Radar for Near-Surface Studies, California State University, San Diego (2003 - 2003)
  • Invited speaker,Physics Department: Environmental Geophysics, Stanford University (2003 - 2003)
  • Organizer DOE Workshop: Geophysical Images of the Near-Surface: What are we really measuring?; Dec 4-7, Berkeley, CA, Department of Energy (2003 - 2003)
  • Public Lecture: Geophysical Images of Water, New Ways to See into the Earth; Dept. of Earth and Ocean Sciences Lecture: The Use of Ground Penetrating Radar for the Development of Hydrogeologic Models; Dept. of Physics Lecture: Nuclear Magnetic Resonance for Environmental Applications, Visiting Scholar, University of Victoria (2003 - 2003)
  • Member (elected), Academic Senate, Stanford University (2002 - 2006)
  • Associate Chair for Undergraduate Programs, Geophysics Dept., Stanford University (2002 - 2005)
  • C-USP Liason to Area 1 (Intro to the Humanities) Governance Board member, Stanford University (2002 - 2004)
  • Co-organizer Near-Surface Geophysics Sessions, AGU-CGU-SEG Assembly, Montreal, AGU-CGU-SEG Assembly (2002 - 2004)
  • Committee Founder, Inter-Society Committee for the Advancement of Near-Surface Geophysics, to promote and advance the science of near-surface geophysics, Inter-Society Committee for the Advancement of Near-Surface Geophysics (2002 - 2004)
  • Member, School of Earth Sciences Diversity Committee, Stanford University (2002 - 2004)
  • Member, University Committee on Undergraduate Standards and Policy (C-USP), Stanford University (2002 - 2004)
  • Keynote speaker: From the Laboratory to the Field: Spatial Heterogeneity in Geophysical Data, Inland Northwest Research Alliance Subsurface Science Symposium, Boise Idaho, Inland Northwest Research Alliance Subsurface Science Symposium (2002 - 2002)
  • Member, Dept of Energy Earth Sciences Council, Stanford University (2001 - 2012)
  • Sexual Harrassment Officer, School of Earth Sciences, Stanford University (2001 - 2003)
  • Member, Computer Committee, School of Earth Sciences, Stanford Unversity (2001 - 2002)
  • Vice-President, Society of Exploration Geophysicists (2001 - 2002)
  • Invited presentation: The Use of Ground Penetrating Radar Data for the Development of Hydrogeologic Models, , December, American Geophysical Union (2001 - 2001)
  • Invited speaker, Workshop on Subsurface Flow and Transport Phenomena, The use of ground penetrating radar data to quantify the scale-dependent spatial heterogeneity of the subsurface, Technical University of Delft, Holland: (2000 - 2000)
  • Organizing Committee for Gordon Conference: Transport in Permeable Media, August, Gordon Conference (2000 - 2000)
  • Visiting Advisory Committee, Dept. of Geophysics, Colorado School of Mines (1999 - 2005)
  • Member of Dean's Advisory Committee for Faculty of Science, University of British Columbia (1999 - 2000)
  • Faculty Advisor for Student Chapter of Environmental and Engineering Geophysical Society, University of British Columbia (1998 - 2000)
  • Member of Executive Committee for Dept. of Earth and Ocean Sciences, University of British Columbia (1998 - 2000)
  • Member, Space Committee, University of British Columbia (1998 - 2000)
  • Chair, Appointment Committee for Lecturer, University of British Columbia (1998 - 1999)
  • Distinguished Lecturer, invited to give 15 lectures, Society of Exploration Geophysicists (1998 - 1999)
  • Member, Re-appointment Committee, University of British Columbia (1998 - 1999)
  • Technical Organizing Committee for Annual Conference, Symposium on Applications of Geophysics to Environmental and Engineering Problems, Environmental and Engineering Geophysical Society (1998 - 1999)
  • Invited speaker, Gordon Conference on Modeling of Flow in Permeable Media, New Hampshire, Gordon Conference (1998 - 1998)
  • Guest editor, special issue on Near-Surface Geophysics, The Leading Edge (1997 - 1997)
  • Invited speaker, Phoebe Apperson Hearst Lecture, U.C. Berkeley, Dept of Materials Science and Mineral Engineering, U.C. Berkeley (1997 - 1997)
  • Member, scientific program review panel, U.S. Dept. of Energy's Environmental Management Science Program, Department of Energy (1997 - 1997)
  • Editorial board, The Leading Edge (1996 - 2000)
  • Member, Lithoprobe Scientific Advisory Committee (1996 - 2000)
  • Member, U.S. National Research Council Committee on Non-Invasive Characterization of the Shallow Subsurface for Environmental and Engineering Applications, U.S. National Research Council (1995 - 1999)
  • Keynote Speaker: 48th Conference, Vancouver: An Assessment of Geophysical Techniques for the Direct Detection of Groundwater Contaminants: A Rock Physics Perspective, Canadian Geotechnical Society (1995 - 1995)
  • Keynote Speaker: BHP Workshop on Women in Science, Tucson, Arizona, BHP Billiton (1995 - 1995)
  • NSERC-sponsored Canada-Mexico Workshop on the Applications of the Physics of Porous Media, PuertoVallerta, Mexico: Elastic Wave Velocities and Fluid Distribution: at the Laboratory and Reservoir Scale, NSERC (1995 - 1995)
  • Distinguished Lecturer, 13 lectures given, Canadian Geophysical Union (1994 - 1995)
  • Vice President of Near-Surface Geophysics Section, American Geophysical Union (1994 - 1995)
  • Faculty founder and advisor of UBC student chapter of Environmental and Engineering Geophysical Society, University of British Columbia (1993 - 2000)
  • Conference Steering Committee for Symposium on the Applications of Geophysics to Environmental and Engineering Problems, Environmental and Engineering Geophysical Society (1993 - 1995)
  • IIMS, U. Manitoba Conference on Porous Media and the Environment: The Link Between Geophysical Data and Pore-Scale Fluid Distribution, IIMS, Univeristy of Manitoba (1993 - 1993)
  • Member, Scientific Program Review Panel, U.S. Department of Energy’s Program on Basic Research, Department of Energy (1993 - 1993)
  • Co-chair of Research Committee, Environmental and Engineering Geophysical Society (1992 - 1995)
  • Board of Directors, Director-at-Large,, Society of Professional Well Log Analysts (1992 - 1993)
  • Public Relations Committee member, Society of Professional Well Log Analysts (1992 - 1993)
  • Scholarships and Grants Committee member, Society of Professional Well Log Analysts (1992 - 1993)
  • Workshop Technical Committee, Workshop on the Physics of Laboratory and Borehole Rock Measurements, August, Society of Professional Well Log Analysts (1992 - 1993)
  • Publications Committee member, Society of Professional Well Log Analysts (1990 - 1993)
  • Member, Society of Core Analysts, Dallas, Texas, (1990 - 1990)
  • Technology Committee member, Society of Professional Well Log Analysts (1989 - 1992)
  • Conference on Electrical Properties, Kerrville Texas, Society of Professional Well Log Analysts (1988 - 1988)

Professional Education

  • Ph.D., Stanford University, Geophysics (1985)
  • M.S., Queen's University, Kingston, Ontario Canada, Geological Sciences (1978)
  • B.S., Queen's University, Kingston, Ontario Canada, Geological Sciences (1976)

Contact

Additional Info

  • Mail Code: 2215

Links

Current Research and Scholarly Interests

Research
I am working with my students to find ways of using geophysical methods to understand the processes occurring in the top 100 meters of Earth. With geophysical methods we can non-invasively acquire images of this near-surface region, allowing us to monitor systems and extract information that cannot be obtained using more traditional methods of drilling and direct sampling. One of our specific interests is the use of geophysical imaging for the evaluation and management of our groundwater resources. Through lab and field experiments, and computer modeling, we are developing new methods for acquiring, processing, and interpreting geophysical data. We are also conducting the laboratory and field experiments needed to determine the link between our geophysical images and subsurface properties and processes.

Teaching
An interest of mine in teaching is ensuring that all university graduates are "geo-literate." Thus a focus of my teaching has always been the education of those who are not Earth science majors. In 2000 I developed and now teach The Water Course, where students complete projects with web posters (http://pangea.stanford.edu/GP/courses/GP104/waterscape/) that describe the source, quantity, and quality of water in their hometowns. Through this course students gain a perspective on water-related issues around the world. I am now leading an effort at Stanford, referred to as I-Earth (Introduction to Planet Earth), where our objective is to offer a set of courses that explore the intersection between natural and human systems. My ultimate goal is to have one of these courses required for all students, so that an understanding of planet Earth is recognized as essential to education in the 21st century.

Professional Activities
Chair, Stanford Faculty Senate (2011-12); Chair, US Dept of Energy Earth Science Council (2010-); Chair, Organizing Committee AGU-SEG Hydrogeophysics Workshop (2011-12); Senior Fellow, Woods Institute for the Environment (2005-present); Co-founder and Chair, Near-Surface Geophysics Focus Group, American Geophysical Union (2005-2007); Stanford Budget Group (2004-); Stanford Faculty Senate (2002-06); Chair, Stanford Committee on Undergraduate Standards and Policy (2004-06); PI, CUAHSI Hydrologic Measurement Facility-Geophysics (2005-); co-organizer, Society of Exploration Geophysicists (SEG) Research Workshop on Hydrogeophysics (2006); U.S. Dept. of Energy Earth Sciences Council (2001-); associate editor, Water Resources Research (2004); vice-president, SEG (2001-02); Frank Frischknecht Award, SEG (2002); editorial board, The Leading Edge (1996-2000); distinguished lecturer, SEG (1998); National Academy of Sciences Committee on Non-Invasive Characterization of the Shallow Subsurface for Environmental and Engineering Applications (1995-99); distinguished lecturer, Canadian Geophysical Union (1994-95); founding member, Environmental and Engineering Geophysical Society (1991)

2024-25 Courses

Stanford Advisees

  • Master's Program Advisor
    Becca Prentice

All Publications

  • Evaluation of models for estimating hydraulic conductivity in glacial aquifers with NMR logging. Ground water Kendrick, A. K., Knight, R., Johnson, C. D., Liu, G., Hart, D. J., Butler, J. J., Hunt, R. J. 2023

    Abstract

    Nuclear magnetic resonance (NMR) logging is a promising method for estimating hydraulic conductivity (K). During the past ~60years, NMR logging has been used for petroleum applications, and different models have been developed for deriving estimates of permeability. These models involve calibration parameters whose values were determined through decades of research on sandstones and carbonates. We assessed the use of five models to derive estimates of K in glacial aquifers from NMR logging data acquired in two wells at each of two field sites in central Wisconsin, USA. Measurements of K, obtained with a direct push permeameter (DPP), KDPP , were used to obtain the calibration parameters in the Schlumberger-Doll Research, Seevers, Timur-Coates, Kozeny-Godefroy, and sum-of-echoes (SOE) models so as to predict K from the NMR data; and were also used to assess the ability of the models to predict KDPP . We obtained four well-scale calibration parameter values for each model by using the NMR and DPP measurements in each well; and one study-scale parameter value for each model by using all data. The SOE model achieved agreement with KDPP that matched or exceeded that of the other models. The Timur-Coates estimates of K were found to be substantially different from KDPP . Although the well-scale parameter values for the Schlumberger-Doll, Seevers, and SOE models were found to vary by less than a factor of 2, more research is needed to confirm their general applicability so that site-specific calibration is not required to obtain accurate estimates of K from NMR logging data. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1111/gwat.13318

    View details for PubMedID 37057729

  • Remote Sensing-Based Estimates of Changes in Stored Groundwater at Local Scales: Case Study for Two Groundwater Subbasins in California's Central Valley REMOTE SENSING Ahamed, A., Knight, R., Alam, S., Morphew, M., Susskind, T. 2023; 15 (8)

    View details for DOI 10.3390/rs15082100

    View details for Web of Science ID 000977163300001

  • Airborne geophysical method images fast paths for managed recharge of California's groundwater ENVIRONMENTAL RESEARCH LETTERS Knight, R., Steklova, K., Miltenberger, A., Kang, S., Goebel, M., Fogg, G. 2022; 17 (12)

    View details for DOI 10.1088/1748-9326/aca344

    View details for Web of Science ID 000912079600001

  • Corrigendum to "Assessing the utility of remote sensing data to accurately estimate changes in groundwater storage" [Sci. Total Environ. 807 (2022) 150635]. The Science of the total environment Ahamed, A., Knight, R., Alam, S., Pauloo, R., Melton, F. 2022; 847: 157678

    View details for DOI 10.1016/j.scitotenv.2022.157678

    View details for PubMedID 35914382

  • Development and Application of a 1D Compaction Model to Understand 65 Years of Subsidence in the San Joaquin Valley WATER RESOURCES RESEARCH Lees, M., Knight, R., Smith, R. 2022; 58 (6)

    View details for DOI 10.1029/2021WR031390

    View details for Web of Science ID 000812257700001

  • Improved Imaging of the Large-Scale Structure of a Groundwater System With Airborne Electromagnetic Data WATER RESOURCES RESEARCH Kang, S., Knight, R., Goebel, M. 2022; 58 (4)

    View details for DOI 10.1029/2021WR031439

    View details for Web of Science ID 000781886400001

  • Managed aquifer recharge site assessment with electromagnetic imaging: Identification of recharge flow paths VADOSE ZONE JOURNAL Pepin, K., Knight, R., Goebel-Szenher, M., Kang, S. 2022

    View details for DOI 10.1002/vzj2.20192

    View details for Web of Science ID 000765256000001

  • The development of a machine-learning approach to construct a field-scale rock-physics transform GEOPHYSICS Gottschalk, I., Knight, R. 2022; 87 (2): MR35-MR48

    View details for DOI 10.1190/GEO2020-0811.1

    View details for Web of Science ID 000777075800001

  • Constructing the resistivity-to-sediment-type transform for the interpretation of airborne electromagnetic data GEOPHYSICS Dewar, N., Knight, R. 2022; 87 (2): IM37-IM55

    View details for DOI 10.1190/GEO2020-0831.1

    View details for Web of Science ID 000776743600005

  • Apportioning deformation among depth intervals in an aquifer system using InSAR and head data HYDROGEOLOGY JOURNAL Smith, R. G., Hashemi, H., Chen, J., Knight, R. 2021

    View details for DOI 10.1007/s10040-021-02386-0

    View details for Web of Science ID 000692637800001

  • Enhancing the resolving ability of electrical resistivity tomography for imaging saltwater intrusion through improvements in inversion methods: A laboratory and numerical study GEOPHYSICS Goebel, M., Knight, R., Kang, S. 2021; 86 (5): WB101-WB115

    View details for DOI 10.1190/GEO2020-0588.1

    View details for Web of Science ID 000711980200063

  • Recharge site assessment through the integration of surface geophysics and cone penetrometer testing VADOSE ZONE JOURNAL Goebel, M., Knight, R. 2021

    View details for DOI 10.1002/vzj2.20131

    View details for Web of Science ID 000658047200001

  • The effect of power lines on time-domain airborne electromagnetic data GEOPHYSICS Kang, S., Dewar, N., Knight, R. 2021; 86 (2): E123-E141

    View details for DOI 10.1190/GEO2020-0089.1

    View details for Web of Science ID 000663815900008

  • Assessing the utility of remote sensing data to accurately estimate changes in groundwater storage. The Science of the total environment Ahamed, A., Knight, R., Alam, S., Pauloo, R., Melton, F. 2021: 150635

    Abstract

    Accurate and timely estimates of groundwater storage changes are critical to the sustainable management of aquifers worldwide, but are hindered by the lack of in-situ groundwater measurements in most regions. Hydrologic remote sensing measurements provide a potential pathway to quantify groundwater storage changes by closing the water balance, but the degree to which remote sensing data can accurately estimate groundwater storage changes is unclear. In this study, we quantified groundwater storage changes in California's Central Valley at two spatial scales for the period 2002 through 2020 using remote sensing data and an ensemble water balance method. To evaluate performance, we compared estimates of groundwater storage changes to three independent estimates: GRACE satellite data, groundwater wells and a groundwater flow model. Results suggest evapotranspiration has the highest uncertainty among water balance components, while precipitation has the lowest. We found that remote sensing-based groundwater storage estimates correlated well with independent estimates; annual trends during droughts fall within 15% of trends calculated using wells and groundwater models within the Central Valley. Remote sensing-based estimates also reliably estimated the long-term trend, seasonality, and rate of groundwater depletion during major drought events. Additionally, our study suggests that the proposed method estimate changes in groundwater at sub-annual latencies, which is not currently possible using other methods. The findings have implications for improving the understanding of aquifer dynamics and can inform regional water managers about the status of groundwater systems during droughts.

    View details for DOI 10.1016/j.scitotenv.2021.150635

    View details for PubMedID 34606871

  • Estimation of the top of the saturated zone from airborne electromagnetic data GEOPHYSICS Dewar, N., Knight, R. 2020; 85 (5): EN63–EN76

    View details for DOI 10.1190/GEO2019-0539.1

    View details for Web of Science ID 000588496500030

  • Using an airborne electromagnetic method to map saltwater intrusion in the northern Salinas Valley, California GEOPHYSICS Gottschalk, I., Knight, R., Asch, T., Abraham, J., Cannia, J. 2020; 85 (4): B119–B131

    View details for DOI 10.1190/GEO2019-0272.1

    View details for Web of Science ID 000583755100003

  • Assessment of NMR logging for estimating hydraulic conductivity in glacial aquifers. Ground water Kendrick, A. K., Knight, R., Johnson, C. D., Liu, G., Knobbe, S., Hunt, R. J., Butler, J. J. 2020

    Abstract

    Glacial aquifers are an important source of groundwater in the United States and require accurate characterization to make informed management decisions. One parameter that is crucial for understanding the movement of groundwater is hydraulic conductivity, K. Nuclear magnetic resonance (NMR) logging measures the NMR response associated with the water in geological materials. By utilizing an external magnetic field to manipulate the nuclear spins associated with 1 H, the time-varying decay of the nuclear magnetization is measured. This logging method could provide an effective way to estimate K at submeter vertical resolution, but the models that relate NMR measurements to K require calibration. At two field sites in a glacial aquifer in central Wisconsin, we collected a total of four NMR logs and obtained measurements of K in their immediate vicinity with a direct-push permeameter (DPP). Using a bootstrap algorithm to calibrate the Schlumberger-Doll Research (SDR) NMR-K model, we estimated K to within a factor of 5 of the DPP measurements. The lowest levels of accuracy occurred in the lower-K (K<10-4 m/s) intervals. We also evaluated the applicability of prior SDR model calibrations. We found the NMR calibration parameters varied with K, suggesting the SDR model does not incorporate all the properties of the pore space that control K. Thus, the expected range of K in an aquifer may need to be considered during calibration of NMR-K models. This study is the first step towards establishing NMR logging as an effective method for estimating K in glacial aquifers.

    View details for DOI 10.1111/gwat.13014

    View details for PubMedID 32390161

  • TOWARDS SUSTAINABLE GROUNDWATER MANAGEMENT: PREDICTING DEFORMATION SCENARIOS WITH COUPLED HYDROGEOPHYSICAL MODELS Smith, R., Knight, R., IEEE IEEE. 2020: 5061-5064

    View details for DOI 10.1109/IGARSS39084.2020.9324482

    View details for Web of Science ID 000664335304216

  • Quantification of Peat Thickness and Stored Carbon at the Landscape Scale in Tropical Peatlands: A Comparison of Airborne Geophysics and an Empirical Topographic Method JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE Silvestri, S., Knight, R., Viezzoli, A., Richardson, C. J., Anshari, G. Z., Dewar, N., Flanagan, N., Comas, X. 2019

    View details for DOI 10.1029/2019JF005273

    View details for Web of Science ID 000505031600001

  • Mapping saltwater intrusion with an airborne electromagnetic method in the offshore coastal environment, Monterey Bay, California JOURNAL OF HYDROLOGY-REGIONAL STUDIES Goebel, M., Knight, R., Halkjaer, M. 2019; 23

    View details for DOI 10.1016/j.ejrh.2019.100602

    View details for Web of Science ID 000469313900004

  • Assessment of Managed Aquifer Recharge Sites Using a New Geophysical Imaging Method VADOSE ZONE JOURNAL Behroozmand, A. A., Auken, E., Knight, R. 2019; 18 (1)

    View details for DOI 10.2136/vzj2018.10.0184

    View details for Web of Science ID 000470241400001

  • Mapping Aquifer Systems with Airborne Electromagnetics in the Central Valley of California GROUNDWATER Knight, R., Smith, R., Asch, T., Abraham, J., Cannia, J., Viezzoli, A., Fogg, G. 2018; 56 (6): 893–908

    View details for DOI 10.1111/gwat.12656

    View details for Web of Science ID 000449769000007

  • Overpumping leads to California groundwater arsenic threat. Nature communications Smith, R., Knight, R., Fendorf, S. 2018; 9 (1): 2089

    Abstract

    Water resources are being challenged to meet domestic, agricultural, and industrial needs. To complement finite surface water supplies that are being stressed by changes in precipitation and increased demand, groundwater is increasingly being used. Sustaining groundwater use requires considering both water quantity and quality. A unique challenge for groundwater use, as compared with surface water, is the presence of naturally occurring contaminants within aquifer sediments, which can enter the water supply. Here we find that recent groundwater pumping, observed through land subsidence, results in an increase in aquifer arsenic concentrations in the San Joaquin Valley of California. By comparison, historic groundwater pumping shows no link to current groundwater arsenic concentrations. Our results support the premise that arsenic can reside within pore water of clay strata within aquifers and is released due to overpumping. We provide a quantitative model for using subsidence as an indicator of arsenic concentrations correlated with groundwater pumping.

    View details for PubMedID 29872050

  • Mapping Aquifer Systems with Airborne Electromagnetics in the Central Valley of California. Ground water Knight, R., Smith, R., Asch, T., Abraham, J., Cannia, J., Viezzoli, A., Fogg, G. 2018

    Abstract

    The passage of the Sustainable Groundwater Management Act in California has highlighted a need for cost-effective ways to acquire the data used in building conceptual models of the aquifer systems in the Central Valley of California. One approach would be the regional implementation of the airborne electromagnetic (AEM) method. We acquired 104 line-kilometers of data in the Tulare Irrigation District, in the Central Valley, to determine the depth of investigation (DOI) of the AEM method, given the abundance of electrically conductive clays, and to assess the usefulness of the method for mapping the hydrostratigraphy. The data were high quality providing, through inversion of the data, models displaying the variation in electrical resistivity to a depth of approximately 500m. In order to transform the resistivity models to interpreted sections displaying lithology, we established the relationship between resistivity and lithology using collocated lithology logs (from drillers' logs) and AEM data. We modeled the AEM response and employed a bootstrapping approach to solve for the range of values in the resistivity model corresponding to sand and gravel, mixed coarse and fine, and clay in the unsaturated and saturated regions. The comparison between the resulting interpretation and an existing cross section demonstrates that AEM can be an effective method for mapping the large-scale hydrostratigraphy of aquifer systems in the Central Valley. The methods employed and developed in this study have widespread application in the use of the AEM method for groundwater management in similar geologic settings.

    View details for PubMedID 29520761

  • The Temporal and Spatial Variability of the Confined Aquifer Head and Storage Properties in the San Luis Valley, Colorado Inferred From Multiple InSAR Missions WATER RESOURCES RESEARCH Chen, J., Knight, R., Zebker, H. A. 2017; 53 (11): 9708–20

    View details for DOI 10.1002/2017WR020881

    View details for Web of Science ID 000418736700058

  • Bias Correction of Long-Term Satellite Monthly Precipitation Product (TRMM 3B43) over the Conterminous United States JOURNAL OF HYDROMETEOROLOGY Hashemi, H., Nordin, M., Lakshmi, V., Huffman, G. J., Knight, R. 2017; 18 (9): 2491–2509

    View details for DOI 10.1175/JHM-D-17-0025.1

    View details for Web of Science ID 000417351800009

  • Investigating the effect of internal gradients on static gradient nuclear magnetic resonance diffusion measurements GEOPHYSICS Fay, E. L., Grombacher, D. J., Knight, R. J. 2017; 82 (5): D293–D301

    View details for DOI 10.1190/GEO2016-0420.1

    View details for Web of Science ID 000417972900016

  • A Laboratory Study of the Link Between NMR Relaxation Data and Pore Size In Carbonate Skeletal Grains and Micrite PETROPHYSICS El-Husseiny, A., Knight, R. 2017; 58 (2): 116-125

    View details for Web of Science ID 000399860700004

  • Estimating the permanent loss of groundwater storage in the southern San Joaquin Valley, California WATER RESOURCES RESEARCH Smith, R. G., Knight, R., Chen, J., Reeves, J. A., Zebker, H. A., Farr, T., Liu, Z. 2017; 53 (3): 2133-2148

    View details for DOI 10.1002/2016WR019861

    View details for Web of Science ID 000400160500024

  • Successful Sampling Strategy Advances Laboratory Studies of NMR Logging in Unconsolidated Aquifers Geophysical Research Letters Behroozmand, A. A., Knight, R., Müller-Petke, M., Auken, E., Barfod, A., Ferré, T., Vilhelmsen, T., Johnson, C., Christiansen, A. V. 2017

    View details for DOI 10.1002/2017GL074999

  • Integrating Non-Colocated Well and Geophysical Data to Capture Subsurface Heterogeneity at an Aquifer Recharge and Recovery Site Journal of Hydrology Gottschalk, I. P., Hermans, T., Knight, R., Caers, J., Cameron, D. A., Regnery, J., McCray, J. E. 2017; 555: 407-419

    View details for DOI 10.1016/j.jhydrol.2017.10.028

  • Characterizing Heterogeneity in Infiltration Rates During Managed Aquifer Recharge GROUNDWATER Mawer, C., Parsekian, A., Pidlisecky, A., Knight, R. 2016; 54 (6): 818-829

    Abstract

    Infiltration rate is the key parameter that describes how water moves from the surface into a groundwater aquifer during managed aquifer recharge (MAR). Characterization of infiltration rate heterogeneity in space and time is valuable information for MAR system operation. In this study, we utilized fiber optic distributed temperature sensing (FO-DTS) observations and the phase shift of the diurnal temperature signal between two vertically co-located fiber optic cables to characterize infiltration rate spatially and temporally in a MAR basin. The FO-DTS measurements revealed spatial heterogeneity of infiltration rate: approximately 78% of the recharge water infiltrated through 50% of the pond bottom on average. We also introduced a metric for quantifying how the infiltration rate in a recharge pond changes over time, which enables FO-DTS to be used as a method for monitoring MAR and informing maintenance decisions. By monitoring this metric, we found high-spatial variability in how rapidly infiltration rate changed during the test period. We attributed this variability to biological pore clogging and found a relationship between high initial infiltration rate and the most rapid pore clogging. We found a strong relationship (R(2)  = 0.8) between observed maximum infiltration rates and electrical resistivity measurements from electrical resistivity tomography data taken in the same basin when dry. This result shows that the combined acquisition of DTS and ERT data can improve the design and operation of a MAR pond significantly by providing the critical information needed about spatial variability in parameters controlling infiltration rates.

    View details for DOI 10.1111/gwat.12423

    View details for Web of Science ID 000390818000010

    View details for PubMedID 27119425

  • Detecting and quantifying organic contaminants in sediments with nuclear magnetic resonance GEOPHYSICS Fay, E. L., Knight, R. J. 2016; 81 (6): EN87-EN97

    View details for DOI 10.1190/GEO2015-0647.1

    View details for Web of Science ID 000392926400020

  • The impact of pore-scale magnetic field inhomogeneity on the shape of the nuclear magnetic resonance relaxation time distribution GEOPHYSICS Grombacher, D., Fay, E., Nordin, M., Knight, R. 2016; 81 (5): EN43-EN55

    View details for DOI 10.1190/GEO2015-0466.1

    View details for Web of Science ID 000392752200032

  • Models and methods for predicting hydraulic conductivity in near-surface unconsolidated sediments using nuclear magnetic resonance GEOPHYSICS Maurer, J., Knight, R. 2016; 81 (5): D503-D518

    View details for DOI 10.1190/GEO2015-0515.1

    View details for Web of Science ID 000392752200017

  • Frequency cycling for compensation of undesired off-resonance effects in surface nuclear magnetic resonance GEOPHYSICS Grombacher, D., Mueller-Petke, M., Knight, R. 2016; 81 (4): WB33-WB48

    View details for DOI 10.1190/GEO2015-0181.1

    View details for Web of Science ID 000386341700073

  • Confined aquifer head measurements and storage properties in the San Luis Valley, Colorado, from spaceborne InSAR observations WATER RESOURCES RESEARCH Chen, J., Knight, R., Zebker, H. A., Schreueder, W. A. 2016; 52 (5): 3623-3636

    View details for DOI 10.1002/2015WR018466

    View details for Web of Science ID 000379259800020

  • Electrical Resistivity Imaging of Seawater Intrusion into the Monterey Bay Aquifer System GROUNDWATER Pidlisecky, A., Moran, T., Hansen, B., Knight, R. 2016; 54 (2): 255-261

    View details for DOI 10.1111/gwat.12351

    View details for Web of Science ID 000373211200013

  • NMR Logging to Estimate Hydraulic Conductivity in Unconsolidated Aquifers GROUNDWATER Knight, R., Walsh, D. O., Butler, J. J., Grunewald, E., Liu, G., Parsekian, A. D., Reboulet, E. C., Knobbe, S., Barrows, M. 2016; 54 (1): 104-114

    View details for DOI 10.1111/gwat.12324

    View details for Web of Science ID 000367969300013

  • A persistent scatterer interpolation for retrieving accurate ground deformation over InSAR-decorrelated agricultural fields GEOPHYSICAL RESEARCH LETTERS Chen, J., Zebker, H. A., Knight, R. 2015; 42 (21): 9294-9301

    View details for DOI 10.1002/2015GL065031

    View details for Web of Science ID 000368336800063

  • The impact of off-resonance effects on water content estimates in surface nuclear magnetic resonance GEOPHYSICS Grombacher, D., Knight, R. 2015; 80 (6): E329-E342

    View details for DOI 10.1190/GEO2014-0402.1

    View details for Web of Science ID 000368347800012

  • Investigating internal magnetic field gradients in aquifer sediments GEOPHYSICS Fay, E. L., Knight, R. J., Song, Y. 2015; 80 (3): D281-D294

    View details for DOI 10.1190/GEO2014-0445.1

    View details for Web of Science ID 000356364300015

  • Relating relative hydraulic and electrical conductivity in the unsaturated zone WATER RESOURCES RESEARCH Mawer, C., Knight, R., Kitanidis, P. K. 2015; 51 (1): 599-618

    View details for DOI 10.1002/2014WR015658

    View details for Web of Science ID 000349889800033

  • Frequency-cycling for compensation of off-resonance effects in surface NMR Geophysics SUBMITTED Grombacher, D., Mueller-Petke, M., Knight, R. 2015
  • The impact of off-resonance effects on water content estimates in surface nuclear magnetic resonance Geophysics IN REVIEW Grombacher, D., Knight, R. 2015
  • Basin scale geophysical imaging of saltwater intrusion, Monterey County, CA Groundwater IN REVISION Pidlisecky, A., Moran, T., Hanson, B., Knight, R. 2015
  • Bootstrap calibration and uncertainty estimation of downhole NMR hydraulic conductivity estimates in an unconsolidated aquifer. Ground water Parsekian, A. D., Dlubac, K., Grunewald, E., Butler, J. J., Knight, R., Walsh, D. O. 2015; 53 (1): 111-121

    Abstract

    Characterization of hydraulic conductivity (K) in aquifers is critical for evaluation, management, and remediation of groundwater resources. While estimates of K have been traditionally obtained using hydraulic tests over discrete intervals in wells, geophysical measurements are emerging as an alternative way to estimate this parameter. Nuclear magnetic resonance (NMR) logging, a technology once largely applied to characterization of deep consolidated rock petroleum reservoirs, is beginning to see use in near-surface unconsolidated aquifers. Using a well-known rock physics relationship-the Schlumberger Doll Research (SDR) equation-K and porosity can be estimated from NMR water content and relaxation time. Calibration of SDR parameters is necessary for this transformation because NMR relaxation properties are, in part, a function of magnetic mineralization and pore space geometry, which are locally variable quantities. Here, we present a statistically based method for calibrating SDR parameters that establishes a range for the estimated parameters and simultaneously estimates the uncertainty of the resulting K values. We used co-located logging NMR and direct K measurements in an unconsolidated fluvial aquifer in Lawrence, Kansas, USA to demonstrate that K can be estimated using logging NMR to a similar level of uncertainty as with traditional direct hydraulic measurements in unconsolidated sediments under field conditions. Results of this study provide a benchmark for future calibrations of NMR to obtain K in unconsolidated sediments and suggest a method for evaluating uncertainty in both K and SDR parameter values.

    View details for DOI 10.1111/gwat.12165

    View details for PubMedID 24520904

  • Investigating internal magnetic field gradients in aquifer sediments Geophysics Re-submitted after minor revisions Fay, E., Knight, R., Song, Y. 2015
  • NMR Logging to Estimate Hydraulic Conductivity in Unconsolidated Aquifers Groundwater Knight, R., Walsh, D., Butler, Jr., J., Grunewald, E., Liu, G., Reboulet, E., Knobbe, S., Barrows, M. 2015
  • Basin scale geophysical imaging of saltwater intrusion, Monterey County, CA Groundwater, IN REVISION Pidlisecky, A., Moran, T., Hanson, B., Knight, R. 2015
  • Relating relative hydraulic and electrical conductivity in the unsaturated zone Water Resources Research Mawer, C., Knight, R., Kitanidis, P. 2015; 51 : 599–618

    View details for DOI 10.1002/2014WR015658

  • Imparting a phase during excitation for improved resolution in surface nuclear magnetic resonance GEOPHYSICS Grombacher, D., Walbrecker, J. O., Knight, R. 2014; 79 (6): E329-E339

    View details for DOI 10.1190/GEO2013-0452.1

    View details for Web of Science ID 000345908500020

  • Monitoring managed aquifer recharge with electrical resistivity probes INTERPRETATION-A JOURNAL OF SUBSURFACE CHARACTERIZATION Nenna, V., Pidlisecky, A., Knight, R. 2014; 2 (4): T155-T166

    View details for DOI 10.1190/INT-2013-0192.1

    View details for Web of Science ID 000364277400032

  • An Analysis of the Uncertainty in InSAR Deformation Measurements for Groundwater Applications in Agricultural Areas IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING Reeves, J. A., Knight, R., Zebker, H. A. 2014; 7 (7): 2992-3001

    View details for DOI 10.1109/JSTARS.2014.2322775

    View details for Web of Science ID 000341568700026

  • Geophysical and Hydrochemical Identification of Flow Paths with Implications for Water Quality at an ARR Site GROUND WATER MONITORING AND REMEDIATION Parsekian, A. D., Regnery, J., Wing, A. D., Knight, R., Drewes, J. E. 2014; 34 (3): 105-116

    View details for DOI 10.1111/gwmr.12071

    View details for Web of Science ID 000341238000026

  • Estimating temporal changes in hydraulic head using InSAR data in the San Luis Valley, Colorado WATER RESOURCES RESEARCH Reeves, J. A., Knight, R., Zebker, H. A., Kitanidis, P. K., Schreueder, W. A. 2014; 50 (5): 4459-4473

    View details for DOI 10.1002/2013WR014938

    View details for Web of Science ID 000337672900047

  • Direct measurement of internal magnetic fields in natural sands using scanning SQUID microscopy. Journal of magnetic resonance Walbrecker, J. O., Kalisky, B., Grombacher, D., Kirtley, J., Moler, K. A., Knight, R. 2014; 242: 10-17

    Abstract

    NMR experiments are ideally carried out in well-controlled magnetic fields. When samples of natural porous materials are studied, the situation can be complicated if the sample itself contains magnetic components, giving rise to internal magnetic fields in the pore space that modulate the externally applied fields. If not properly accounted for, the internal fields can lead to misinterpretation of relaxation, diffusion, or imaging data. To predict the potential effect of internal fields, and develop effective mitigation strategies, it is important to develop a quantitative understanding of the magnitude and distribution of internal fields occurring in natural porous media. To develop such understanding, we employ scanning SQUID microscopy, a technique that can detect magnetic field variations very accurately at high spatial resolution (∼3μm). We prepared samples from natural unconsolidated aquifer material, and scanned areas of about 200×200μm in a very low background magnetic field of ∼2μT. We found large amplitude variations with a magnitude of about 2mT, across a relatively long spatial scale of about 200μm, that are associated with a large magnetic grain (>50μm radius) with a strong magnetic remanence. We also detected substantial variations exceeding 60μT on small spatial scales of about ∼10μm. We attribute these small-scale variations to very fine-grained magnetic material. Because we made our measurements at very low background field, the observed variations are not induced by the background field but due to magnetic remanence. Consequently, the observed internal fields will affect even low-field NMR experiments.

    View details for DOI 10.1016/j.jmr.2014.01.012

    View details for PubMedID 24589519

  • The impact of prepolarization on Earth's field laboratory nuclear-magnetic-resonance relaxation experiments GEOPHYSICS Walbrecker, J. O., Knight, R., Grunewald, E. 2014; 79 (3): EN39-EN48

    View details for DOI 10.1190/GEO2013-0272.1

    View details for Web of Science ID 000338322900017

  • A numerical study of the relationship between NMR relaxation and permeability in sands and gravels NEAR SURFACE GEOPHYSICS Dlubac, K., Knight, R., Keating, K. 2014; 12 (2): 219-230

    View details for DOI 10.3997/1873-0604.2013042

    View details for Web of Science ID 000339623700005

  • Advancement and validation of surface nuclear magnetic resonance spin-echo measurements of T-2 GEOPHYSICS Grunewald, E., Knight, R., Walsh, D. 2014; 79 (2): EN15-EN23

    View details for DOI 10.1190/GEO2013-0105.1

    View details for Web of Science ID 000336918700023

  • Quantifying background magnetic-field inhomogeneity for improved interpretation of free induction decay measurements GEOPHYSICS Grombacher, D., Walbrecker, J. O., Knight, R. 2014; 79 (1): E11-E21

    View details for DOI 10.1190/GEO2012-0488.1

    View details for Web of Science ID 000336912400009

  • Demonstration of a value of information metric to assess the use of geophysical data for a groundwater application GEOPHYSICS Nenna, V., Knight, R. 2014; 79 (1): E51-E60

    View details for DOI 10.1190/GEO2012-0474.1

    View details for Web of Science ID 000336912400012

  • The inversion of surface-NMR T-1 data for improved aquifer characterization GEOPHYSICS Mueller-Petke, M., Walbrecker, J. O., Knight, R. 2013; 78 (6): EN83-EN94

    View details for DOI 10.1190/GEO2013-0035.1

    View details for Web of Science ID 000330223800022

  • Calibrating a Salt Water Intrusion Model with Time-Domain Electromagnetic Data GROUND WATER Herckenrath, D., Odlum, N., Nenna, V., Knight, R., Auken, E., Bauer-Gottwein, P. 2013; 51 (3): 385-397

    Abstract

    Salt water intrusion models are commonly used to support groundwater resource management in coastal aquifers. Concentration data used for model calibration are often sparse and limited in spatial extent. With airborne and ground-based electromagnetic surveys, electrical resistivity models can be obtained to provide high-resolution three-dimensional models of subsurface resistivity variations that can be related to geology and salt concentrations on a regional scale. Several previous studies have calibrated salt water intrusion models with geophysical data, but are typically limited to the use of the inverted electrical resistivity models without considering the measured geophysical data directly. This induces a number of errors related to inconsistent scales between the geophysical and hydrologic models and the applied regularization constraints in the geophysical inversion. To overcome these errors, we perform a coupled hydrogeophysical inversion (CHI) in which we use a salt water intrusion model to interpret the geophysical data and guide the geophysical inversion. We refer to this methodology as a Coupled Hydrogeophysical Inversion-State (CHI-S), in which simulated salt concentrations are transformed to an electrical resistivity model, after which a geophysical forward response is calculated and compared with the measured geophysical data. This approach was applied for a field site in Santa Cruz County, California, where a time-domain electromagnetic (TDEM) dataset was collected. For this location, a simple two-dimensional cross-sectional salt water intrusion model was developed, for which we estimated five uniform aquifer properties, incorporating the porosity that was also part of the employed petrophysical relationship. In addition, one geophysical parameter was estimated. The six parameters could be resolved well by fitting more than 300 apparent resistivities that were comprised by the TDEM dataset. Except for three sounding locations, all the TDEM data could be fitted close to a root-mean-square error of 1. Possible explanations for the poor fit of these soundings are the assumption of spatial uniformity, fixed boundary conditions and the neglecting of 3D effects in the groundwater model and the TDEM forward responses.

    View details for DOI 10.1111/j.1745-6584.2012.00974.x

    View details for Web of Science ID 000318172100011

    View details for PubMedID 22891736

  • A methodology for quantifying the value of spatial information for dynamic Earth problems STOCHASTIC ENVIRONMENTAL RESEARCH AND RISK ASSESSMENT Trainor-Guitton, W. J., Mukerji, T., Knight, R. 2013; 27 (4): 969-983

    View details for DOI 10.1007/s00477-012-0619-4

    View details for Web of Science ID 000317749400015

  • Use of NMR logging to obtain estimates of hydraulic conductivity in the High Plains aquifer, Nebraska, USA WATER RESOURCES RESEARCH Dlubac, K., Knight, R., Song, Y., Bachman, N., Grau, B., Cannia, J., Williams, J. 2013; 49 (4): 1871-1886

    View details for DOI 10.1002/wrcr.20151

    View details for Web of Science ID 000319282100009

  • Application and evaluation of electromagnetic methods for imaging saltwater intrusion in coastal aquifers: Seaside Groundwater Basin, California GEOPHYSICS Nenna, V., Herckenrath, D., Knight, R., Odlum, N., McPhee, D. 2013; 78 (2): B77-B88

    View details for DOI 10.1190/GEO2012-0004.1

    View details for Web of Science ID 000319858000003

  • Detecting unfrozen sediments below thermokarst lakes with surface nuclear magnetic resonance GEOPHYSICAL RESEARCH LETTERS Parsekian, A. D., Grosse, G., Walbrecker, J. O., Mueller-Petke, M., Keating, K., Liu, L., Jones, B. M., Knight, R. 2013; 40 (3): 535-540

    View details for DOI 10.1002/grl.50137

    View details for Web of Science ID 000317831000014

  • Electrical Resistivity for Characterization and Infiltration Monitoring beneath a Managed Aquifer Recharge Pond VADOSE ZONE JOURNAL Mawer, C., Kitanidis, P., Pidlisecky, A., Knight, R. 2013; 12 (1)

    View details for DOI 10.2136/vzj2011.0203

    View details for Web of Science ID 000317713300006

  • Electrical Conductivity Probes for Studying Vadose Zone Processes: Advances in Data Acquisition and Analysis VADOSE ZONE JOURNAL Pidlisecky, A., Cockett, A. R., Knight, R. 2013; 12 (1)

    View details for DOI 10.2136/vzj2012.0073

    View details for Web of Science ID 000317713300024

  • Composite pulses to quantify background magnetic field inhomogeneity Geophysics Grombacher, D., Walbrecker, J., Knight, R. 2013
  • The effect of spatial variation in surface relaxivity on nuclear magnetic resonance relaxation rates GEOPHYSICS Keating, K., Knight, R. 2012; 77 (5): E365-E377

    View details for DOI 10.1190/GEO2011-0462.1

    View details for Web of Science ID 000309077200013

  • Field experiment provides ground truth for surface nuclear magnetic resonance measurement GEOPHYSICAL RESEARCH LETTERS Knight, R., Grunewald, E., Irons, T., Dlubac, K., Song, Y., Bachman, H. N., Grau, B., Walsh, D., Abraham, J. D., Cannia, J. 2012; 39

    View details for DOI 10.1029/2011GL050167

    View details for Web of Science ID 000299992100001

  • Nonexponential decay of the surface-NMR signal and implications for water content estimation GEOPHYSICS Grunewald, E., Knight, R. 2012; 77 (1): EN1-EN9

    View details for DOI 10.1190/GEO2011-0160.1

    View details for Web of Science ID 000300767000017

  • Conditions leading to non-exponential T2 relaxation and implications for surface NMR measurements Geophysics Grunewald, E., Knight, R. 2012; 77

    View details for DOI 10.1190/GEO2011-0160.1

  • Field experiment provides ground truth for surface NMR measurement Geophysical Research Letters Knight, R., Grunewald, E., Irons, T., Dlubac., K, Song, Y., Bachman, H., Grau, B., Walsh, D., Abraham, J., Cannia, J. 2012

    View details for DOI 10.1029/2011GL050167

  • Calibrating a saltwater intrusion model with time domain electromagnetic data Groundwater Herckenrath, D., Odlum, N., Nenna, V., Auken, E., Knight, R., Bauer-Gottwein, P. 2012

    View details for DOI 10.1111/j.1745-6584.2012.00974

  • High quality InSAR data linked to seasonal change in hydraulic head for an agricultural area in the San Luis Valley, Colorado WATER RESOURCES RESEARCH Reeves, J. A., Knight, R., Zebker, H. A., Schreueder, W. A., Agram, P. S., Lauknes, T. R. 2011; 47

    View details for DOI 10.1029/2010WR010312

    View details for Web of Science ID 000298256100001

  • Application of an extended Kalman filter approach to inversion of time-lapse electrical resistivity imaging data for monitoring recharge WATER RESOURCES RESEARCH Nenna, V., Pidlisecky, A., Knight, R. 2011; 47

    View details for DOI 10.1029/2010WR010120

    View details for Web of Science ID 000296339500001

  • Informed experimental design for electrical resistivity imaging NEAR SURFACE GEOPHYSICS Nenna, V., Pidlisecky, A., Knight, R. 2011; 9 (5): 469-482

    View details for DOI 10.3997/1873-0604.2011027

    View details for Web of Science ID 000300855600007

  • A laboratory study of NMR relaxation times in unconsolidated heterogeneous sediments GEOPHYSICS Grunewald, E., Knight, R. 2011; 76 (4): G73-G83

    View details for DOI 10.1190/1.3581094

    View details for Web of Science ID 000292156200013

  • The Use of Wavelet Analysis to Derive Infiltration Rates from Time-Lapse One-Dimensional Resistivity Records VADOSE ZONE JOURNAL Pidlisecky, A., Knight, R. 2011; 10 (2): 697-705

    View details for DOI 10.2136/vzj2010.0049

    View details for Web of Science ID 000291396000022

  • The effect of pore size and magnetic susceptibility on the surface NMR relaxation parameter T-2* 4th Workshop for Magnetic Resonance Sounding Grunewald, E., Knight, R. EUROPEAN ASSOC GEOSCIENTISTS & ENGINEERS. 2011: 169–78

    View details for DOI 10.3997/1873-0604.2010062

    View details for Web of Science ID 000300855300009

  • Linking interferometric synthetic aperture radar data and seasonal head change for an agricultural area in the San Luis Valley, Colorado Water Resources Research Reeves, J. A., Knight, R., Zebker, H. A., Schreüder, W. A., Agram, P. S., Lauknes, T. R. 2011; 47

    View details for DOI 10.1029/2010WR010312

  • GEOPHYSICS AT THE INTERFACE: RESPONSE OF GEOPHYSICAL PROPERTIES TO SOLID-FLUID, FLUID-FLUID, AND SOLID-SOLID INTERFACES REVIEWS OF GEOPHYSICS Knight, R., Pyrak-Nolte, L. J., Slater, L., Atekwana, E., Endres, A., Geller, J., Lesmes, D., Nakagawa, S., Revil, A., Sharma, M. M., Straley, C. 2010; 48

    View details for DOI 10.1029/2007RG000242

    View details for Web of Science ID 000285017700001

  • A laboratory study of the effect of Fe(II)-bearing minerals on nuclear magnetic resonance (NMR) relaxation measurements GEOPHYSICS Keating, K., Knight, R. 2010; 75 (3): F71-F82

    View details for DOI 10.1190/1.3386573

    View details for Web of Science ID 000278887000017

  • Improved interpretation of resistivity cone penetration testing logs through forward modeling and inversion Journal of Applied Geophysics Pidlisecky, A., Knight, R., Howie, J. A. 2010
  • Inversion of time-lapse electrical resistivity imaging data for monitoring infiltration Society of Exploration Geophysicists Annual Convention Mitchell, V., Pidlisecky, A., Knight, R. 2010: 1950

    View details for DOI 10.1190/1.3513225

  • An assessment of the use of the Kozeny-Carman equation to estimate permeability in anisotropic materials from Society of Exploration Geophysicists Annual Convention Dlubac, K. I., Knight, R. J. 2010: 2644–48

    View details for DOI 10.1190/1.3513390

  • Conditions leading to non-exponential decay of the surface-NMR signal and implications for water content estimation Society of Exploration Geophysicists Annual Convention Grunewald, E. D., Knight, R. 2010
  • Estimation of the lateral correlation structure of subsurface water content from surface-based ground-penetrating radar reflection images WATER RESOURCES RESEARCH Irving, J., Knight, R., Holliger, K. 2009; 45

    View details for DOI 10.1029/2008WR007471

    View details for Web of Science ID 000272448600002

  • A laboratory study of NMR relaxation times and pore coupling in heterogeneous media GEOPHYSICS Grunewald, E., Knight, R. 2009; 74 (6): E215-E221

    View details for DOI 10.1190/1.3223712

    View details for Web of Science ID 000273037800006

  • Hydrogeologic structure underlying a recharge pond delineated with shear-wave seismic reflection and cone penetrometer data NEAR SURFACE GEOPHYSICS Haines, S. S., Pidlisecky, A., Knight, R. 2009; 7 (5-6): 329-339

    View details for Web of Science ID 000270895200004

  • Interpreting Earth's field NMR measurements of T2 for hydrogeologic applications 4th International Workshop on Magnetic Resonance Sounding Grunewald, E., Knight, R. 2009
  • Electrical resistivity imaging of the architecture of substream sediments WATER RESOURCES RESEARCH Crook, N., Binley, A., Knight, R., Robinson, D. A., Zarnetske, J., Haggerty, R. 2008; 44

    View details for DOI 10.1029/2008WR006968

    View details for Web of Science ID 000261689700001

  • FW2_5D: A MATLAB 2.5-D electrical resistivity modeling code COMPUTERS & GEOSCIENCES Pidlisecky, A., Knight, R. 2008; 34 (12): 1645-1654

    View details for DOI 10.1016/j.cageo.2008.04.001

    View details for Web of Science ID 000261632000001

  • A laboratory study of the effect of magnetite on NMR relaxation rates JOURNAL OF APPLIED GEOPHYSICS Keating, K., Knight, R. 2008; 66 (3-4): 188-196

    View details for DOI 10.1016/j.jappgeo.2007.09.001

    View details for Web of Science ID 000261354300012

  • Eco-Geophysical Imaging of Watershed-Scale Soil Patterns Links with Plant Community Spatial Patterns VADOSE ZONE JOURNAL Robinson, D. A., Abdu, H., Jones, S. B., Seyfried, M., Lebron, I., Knight, R. 2008; 7 (4): 1132-1138

    View details for DOI 10.2136/vzj2008.0101

    View details for Web of Science ID 000261384600001

  • Nuclear magnetic resonance relaxation measurements as a means of monitoring iron mineralization processes GEOPHYSICAL RESEARCH LETTERS Keating, K., Knight, R., Tufano, K. J. 2008; 35 (19)

    View details for DOI 10.1029/2008GL035225

    View details for Web of Science ID 000260176900004

  • Advancing process-based watershed hydrological research using near-surface geophysics: a vision for, and review of, electrical and magnetic geophysical methods HYDROLOGICAL PROCESSES Robinson, D. A., Binley, A., Crook, N., Day-Lewis, F. D., Ferre, T. P., Grauch, V. J., Knight, R., Knoll, M., Lakshmi, V., Miller, R., Nyquist, J., Pellerin, L., Singha, K., Slater, L. 2008; 22 (18): 3604-3635

    View details for DOI 10.1002/hyp.6963

    View details for Web of Science ID 000259281300005

  • Soil moisture measurement for ecological and hydrological watershed-scale observatories: A review VADOSE ZONE JOURNAL Robinson, D. A., Campbell, C. S., Hopmans, J. W., Hornbuckle, B. K., Jones, S. B., Knight, R., Ogden, F., Selker, J., Wendroth, O. 2008; 7 (1): 358-389

    View details for DOI 10.2136/vzj2007.0143

    View details for Web of Science ID 000254960900037

  • NMR relaxation measurements to quantify immiscible organic contaminants in sediments WATER RESOURCES RESEARCH Bryar, T. R., Knight, R. J. 2008; 44 (2)

    View details for DOI 10.1029/2006WR005635

    View details for Web of Science ID 000252887500001

  • Improving crosshole radar velocity tomograms: A new approach to incorporating high-angle traveltime data GEOPHYSICS Irving, J. D., Knoll, M. D., Knight, R. J. 2007; 72 (4): J31-J41

    View details for DOI 10.1190/1.2742813

    View details for Web of Science ID 000248365000023

  • RESINVM3D: A 3D resistivity inversion package GEOPHYSICS Pidlisecky, A., Haber, E., Knight, R. 2007; 72 (2): H1-H10

    View details for DOI 10.1190/1.2402499

    View details for Web of Science ID 000245441200030

  • A laboratory study to determine the effect of iron oxides on proton NMR measurements GEOPHYSICS Keating, K., Knight, R. 2007; 72 (1): E27-E32

    View details for DOI 10.1190/1.2399445

    View details for Web of Science ID 000243728500010

  • Improving crosshole GPR travel-time tomography between closely spaced boreholes at the Boise Hydrogeophysical Research Site Geophysics Irving, J., Knoll, M., Knight, R. 2007; 72: J31-J41
  • A comparison of the use of radar images and neutron probe data to determine the horizontal correlation length of water content AGU Geophysical Monograph Series Knight, R., Irving, J., Tercier, P., Freeman, G., Murray, C., Rockhold, M. 2007; 171: 31-44
  • Numerical modeling of ground-penetrating radar in 2-D using MATLAB COMPUTERS & GEOSCIENCES Irving, J., Knight, R. 2006; 32 (9): 1247-1258

    View details for DOI 10.1016/j.cageo.2005.11.006

    View details for Web of Science ID 000240760200002

  • Texture-based classification of ground-penetrating radar images GEOPHYSICS Moysey, S., Knight, R. J., Jol, H. M. 2006; 71 (6): K111-K118

    View details for DOI 10.1190/1.2356114

    View details for Web of Science ID 000242598600034

  • Cone-based electrical resistivity tomography GEOPHYSICS Pidlisecky, A., Knight, R., Haber, E. 2006; 71 (4): G157-G167

    View details for DOI 10.1190/1.2213205

    View details for Web of Science ID 000240637500022

  • Numerical simulation of antenna transmission and reception for crosshole ground-penetrating radar GEOPHYSICS Irving, J. D., Knight, R. J. 2006; 71 (2): K37-K45

    View details for DOI 10.1190/1.2187768

    View details for Web of Science ID 000236539700019

  • A vision for geophysics instrumentation in watershed hydrological research A Report to the Consortium of Universities for the Advancement of Hydrologic Sciences, Inc. Robinson, D. A., Binley, A., Crook, N., Day-Lewis, F. D., Ferre, T. A., Grauch, V. S., Knight, R., Knoll, M., Lakshmi, V., Miller, R., Nyquist, J., Pellerin, L., Singha, K., Slater, L. Advancement of Hydrologic Sciences, Inc., Washington, US. 2006
  • Relating geophysical and hydrologic properties using field-scale rock physics CMWR XVI-Computational Methods in Water Resources Moysey, S., Knight, R. J., Singha, K. 2006: 8 p.
  • Effect of antennas on velocity estimates obtained from crosshole GPR data GEOPHYSICS Irving, J. D., Knight, R. J. 2005; 70 (5): K39-K42

    View details for DOI 10.1190/1.2049349

    View details for Web of Science ID 000232294700015

  • A framework for inferring field-scale rock physics relationships through numerical simulation GEOPHYSICAL RESEARCH LETTERS Moysey, S., Singha, K., Knight, R. 2005; 32 (8)

    View details for DOI 10.1029/2004GL022152

    View details for Web of Science ID 000228850900002

  • A Cone-based geophysical imaging: A new solution to a challenging problem The Leading Edge Knight, R. J., Pidlisecky, A. 2005
  • Accounting for the effect of antenna length to improve crosshole GPR velocity estimates SEG 75th Annual Meeting Irving, J., Knight, R. 2005: 2005
  • The effect of vertical measurement resolution on the correlation structure of a ground penetrating radar reflection image GEOPHYSICAL RESEARCH LETTERS Knight, R., Tercier, P., Irving, J. 2004; 31 (21)

    View details for DOI 10.1029/2004GL021112

    View details for Web of Science ID 000225189800004

  • Modeling the field-scale relationship between dielectric constant and water content in heterogeneous systems WATER RESOURCES RESEARCH Moysey, S., Knight, R. 2004; 40 (3)

    View details for DOI 10.1029/2003WR002589

    View details for Web of Science ID 000220442300001

  • An Introduction to Rock Physics for Near-Surface Applications in Near-Surface Geophysics Volume 1: Concepts and Fundamentals Knight, R., Endres, A. edited by Butler, E. D. Society of Exploration Geophysicists. 2004
  • Stochastic estimation of facies using ground penetrating radar data ModelCARE 2002 Conference Moysey, S., Caers, J., Knight, R., Allen-King, R. M. SPRINGER. 2003: 306–18

    View details for DOI 10.1007/s00477-003-0152-6

    View details for Web of Science ID 000186542900004

  • An inclusion-based model of elastic wave velocities incorporating patch-scale fluid pressure relaxation GEOPHYSICS Taylor, S. R., Knight, R. J. 2003; 68 (5): 1503-1509

    View details for DOI 10.1190/1.1620623

    View details for Web of Science ID 000220836400006

  • Incorporating mechanisms of fluid pressure relaxation into inclusion-based models of elastic wave velocities GEOPHYSICS Taylor, S. R., Knight, R. J. 2003; 68 (4): 1173-1181

    View details for DOI 10.1190/1.1598110

    View details for Web of Science ID 000220836300007

  • Removal of wavelet dispersion from ground-penetrating radar data GEOPHYSICS Irving, J. D., Knight, R. J. 2003; 68 (3): 960-970

    View details for DOI 10.1190/1.1581068

    View details for Web of Science ID 000220836200018

  • Laboratory studies of the effect of sorbed oil on proton nuclear magnetic resonance GEOPHYSICS Bryar, T. R., Knight, R. J. 2003; 68 (3): 942-948

    View details for DOI 10.1190/1.1581046

    View details for Web of Science ID 000220836200016

  • The construction of stochastic facies-based models conditioned to ground penetrating radar images Conference on Calibration and Reliability in Groundwater Modelling (ModelCARE 2002) Moysey, S., Knight, R., Allen-King, R. M., Caers, J. INT ASSOC HYDROLOGICAL SCIENCES. 2003: 395–401

    View details for Web of Science ID 000189478600053

  • Assessment of the Use of Cone-Based Resistivity Imaging Symposium on the Application of Geophysics to Engineering and Environmental Problems Pidlisecky, A., Haber, E., Knight, R. J. 2003
  • Detection limits for immiscible liquid organic contaminants using proton nuclear magnetic resonance Symposium on the Application of Geophysics to Engineering and Environmental Problems, San Antonio, TX, Bryar, T. R., Knight, R. J. 2003
  • Laboratory studies of the detection of sorbed oil with proton nuclear magnetic resonance Geophysics Bryar, T. R., Knight, R. J. 2003; 68: 942-948
  • Saturation-dependent anisotropy in borehole radar data Proceedings of the Symposium on the Application of Geophysics to Engineering and Environmental Problems Irving, J. D., Knight, R. J. 2003
  • The use of ground penetrating radar for site characterization at Hanford Symposium on the Application of Geophysics to Engineering and Environmental Problems Knight, R. J., Irving, J., Freeman, E., Tercier, P. 2003
  • Sensitivity of nuclear magnetic resonance relaxation measurements to changing soil redox conditions GEOPHYSICAL RESEARCH LETTERS Bryar, T. R., Knight, R. J. 2002; 29 (24)

    View details for DOI 10.1029/2002GL016043

    View details for Web of Science ID 000181230500008

  • Aquifer heterogeneity from SH-wave seismic impedance inversion GEOPHYSICS Jarvis, K. D., Knight, R. J. 2002; 67 (5): 1548-1557

    View details for DOI 10.1190/1.1512800

    View details for Web of Science ID 000178606500020

  • Aquifer heterogeneity from SH-wave seismic impedance inversion, accepted for publication Geophysics Jarvis, K., Knight, R. J. 2002; 67: 1548-1557
  • Effect of sorbed oil on the dielectric properties of sand and clay WATER RESOURCES RESEARCH Li, C., Tercier, P., Knight, R. 2001; 37 (6): 1783-1793

    View details for Web of Science ID 000168845200022

  • Ground penetrating radar for environmental applications ANNUAL REVIEW OF EARTH AND PLANETARY SCIENCES Knight, R. 2001; 29: 229-255

    View details for Web of Science ID 000168810800009

  • Laboratory measurements of electromagnetic wave velocity in layered sands Water Resources Research Chan, C. Y., Knight, R. J. 2001; 37: 1099-1105
  • The effect of adsorbed oil on the dielectric properties of sand and clay Water Resources Research Li, C., Tercier, P., Knight, R. 2001; 37: 1783-1793
  • A comparison of the correlation structure in GPR images of deltaic and barrier-spit depositional environments GEOPHYSICS Tercier, P., Knight, R., Jol, H. 2000; 65 (4): 1142-1153

    View details for Web of Science ID 000088771100012

  • Detecting sorbed hydrocarbons in a porous medium using proton nuclear magnetic resonance ENVIRONMENTAL SCIENCE & TECHNOLOGY Daughney, C. J., Bryar, T. R., Knight, R. J. 2000; 34 (2): 332-337

    View details for Web of Science ID 000084774500016

  • Estimation and correction of wavelet dispersion in GPR Data GPR 2000, the Eighth International Conference on Ground Penetrating Radar Irving, J., Knight, R. J. 2000: 123–29
  • Paramagnetic effects of iron(III) species on nuclear magnetic relaxation of fluid protons in porous media JOURNAL OF MAGNETIC RESONANCE Bryar, T. R., Daughney, C. J., Knight, R. J. 2000; 142 (1): 74-85

    Abstract

    The (1)H NMR spin-lattice relaxation time, T(1), of saturated sands depended on the chemistry of the pore fluid, pore size distribution, and relaxivity of the surface. In the absence of paramagnetic impurities, surface relaxivities of quartz sand and silica gel samples of known porosity and surface area at any pH were lower than any previously reported values. Relaxation rate of the bulk pore fluid increased linearly with increasing Fe(III) concentration and varied with speciation of the ion. With only 0.01% of the silica surface sites occupied by sorbed Fe(III) ions, surface relaxivity increased by an order of magnitude. In addition, low concentrations of Fe(III)-bearing solid phases present as surface coatings or as separate mineral grains increased surface relaxation as much as two orders of magnitude. We believe that observations of relatively constant surface relaxivity in rocks by previous researchers were the result of consistently high surface concentrations of paramagnetic materials.

    View details for Web of Science ID 000085222700008

    View details for PubMedID 10617437

  • Estimation and correction of wavelet dispersion in GPR data 8th International Conference on Ground Penetrating Radar (GPR 2000) Irving, J., Knight, R. SPIE-INT SOC OPTICAL ENGINEERING. 2000: 561–566

    View details for Web of Science ID 000088778100099

  • Noninvasive characterization of the shallow subsurface for environmental and engineering applications Seeing into the Earth Knight, R. ., et al National Academy Press, Washington, D.C.. 2000: 269p
  • Near-surface VSP surveys using the seismic cone penetrometer Geophysics Jarvis, K., Knight, R. J. 2000; 65: 1048-1056
  • A comparison of the correlation structure in GPR images of deltaic and barrier spit depositional environments Geophysics Tercier, P., Knight, R. J., Jol, H. 2000; 65: 1142-1153
  • Detecting sorbed hydrocarbons in a porous medium using proton nuclear magnetic resonance Environmental Science and Technology Daughney, C., Bryar, T., Knight, R. J. 2000; 34: 332-337
  • Effects of paramagnetic iron (III) species on nuclear magnetic resonance relaxation of saturated sands Journal of Magnetic Resonance Bryar, T., Daughney, C., Knight, R. J. 2000; 142: 74-85
  • Accounting for saturation heterogeneity in obtaining estimate of water content from dielectric data Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP) Chan, C., Knight, R. J. 1999: 435–44
  • Geological landscape of the pre-Inca archeological site at Chavin de Huantar, Peru Geological Survey of Canada, Current Research Turner, R. W., Knight, R. J., Rick, J. 1999: 47-56
  • Geotechnical applications of VSP surveys using the seismic cone penetrometer 12th Symposium on the Application of Geophysics to Engineering and Environmental Problems (SAGEEP) at the Annual Meeting of the EEGS Jarvis, K., Knight, R., Howie, J. ENVIRONMENTAL & ENGINEERING GEOPHYSICAL SOCIETY. 1999: 11–20

    View details for Web of Science ID 000082991400002

  • Dielectric constant as a predictor of porosity in dry volcanic rocks Journal of Volcanology and Geophysical Research Rust, A. C., Russell, J. K., Knight, R. J. 1999; 91: 79-96
  • Determining water content and saturation from dielectric measurements in layered materials Water Resources Research Chan, C. Y., Knight, R. J. 1999; 35: 85-93
  • Acoustic signatures of partial saturation GEOPHYSICS Knight, R., Dvorkin, J., Nur, A. 1998; 63 (1): 132-138

    View details for Web of Science ID 000071711500013

  • Elastic wave velocities during evaporative drying Geophysics Goertz, D., Knight, R. J. 1998; 63: 171-183
  • Characterization of the Brookswood aquifer using ground penetrating radar Aquifer Delineation, Fraser Lowlands and Delta, B.C.: Mapping, Geophysics, and Groundwater Modeling Rea, J., Knight , R. J. edited by Ricketts, B. D. Geological Survey of Canada. 1998
  • Effects of wettability and fluid chemistry on the proton NMR T1 in sands Journal of Environmental and Engineering Geophysics Kanters, W., Knight, R. J., Mackay, A. 1998; 3: 197-202
  • Geostatistical analysis of ground penetrating radar data: a means of describing spatial variation in the subsurface Water Resources Rea, J., Knight, R. J. 1998; 34: 329-339
  • The electrical conductivity of steam-flooded, clay-bearing sands Geophysics Butler, D., Knight, R. J. 1998; 63: 1137-1149
  • Effects of pore structure and wettability on the electrical resistivity of partially saturated rocks--A network study Geophysics Suman, R., Knight, R. J. 1997; 62: 1151-1162
  • Incorporating pore geometry and fluid pressure communication into modeling the elastic behavior of porous rocks GEOPHYSICS Endres, A. L., Knight, R. J. 1997; 62 (1): 106-117

    View details for Web of Science ID A1997WF18800014

  • Incorporating pore geometry and fluid pressure communication into modeling the elastic behavior of porous rocks Geophysics Endres, A. L., Knight, R. J. 1997; 61: 106-117
  • The role of ground penetrating radar and geostatistics in reservoir description The Leading Edge Knight, R., Tercier, P., Jol, H. 1997; 16: 1576-1581
  • A laboratory procedure for estimating irreducible water saturation from cuttings The Log Analyst Knight, R. J., Tercier, P., Goertz, D. 1996; 37: 18-24
  • The use of ground penetrating radar for aquifer characterization: an example from southwestern British Columbia Symposium for Application of Geophysics to Environmental and Engineering Problems, Rea, J., Knight, R. J. 1995: 10pp
  • Rock/water interaction in dielectric properties: Experiments with hydrophobic sandstones Geophysics Knight, R. J., Abad, A. 1995; 60: 431-436
  • A laboratory procedure for estimating irreducible water saturation from cuttings Society of Professional Well Log Analysts 36th Annual Symposium Knight, R. J., Tercier, P., Goertz, D. 1995
  • An Assessment of Geophysical Techniques for the Direct Detection of Groundwater Contaminants: A Rock Physics Perspective Canadian Geotechnical Society 48th Conference Knight, R. J. 1995
  • Can accurate estimates of permeability be obtained from measurements of dielectric properties? Symposium for the Application of Geophysics to Environmental and Engineering Problems Knoll, M. D., Knight, R. J., Brown, E. 1995
  • Continuum percolation conductivity exponents in restricted domains Journal of Statistical Physics Berkowitz, B., Knight, R. J. 1995; 80: 1415-1423
  • The effect of steam quality on the electrical behavior of steam-flooded sands: A laboratory study Geophysics Butler, D. B., Knight, R. J. 1995; 60: 998-1006
  • Dielectric and hydrogeologic properties of sand-clay mixtures Fifith International Conference on Ground Penetrating Radar Knoll, M. D., Knight, R. J. 1994
  • A MODEL FOR INCORPORATING SURFACE PHENOMENA INTO THE DIELECTRIC RESPONSE OF A HETEROGENEOUS MEDIUM JOURNAL OF COLLOID AND INTERFACE SCIENCE Endres, A. L., Knight, R. J. 1993; 157 (2): 418-425

    View details for Web of Science ID A1993KZ32800021

  • Incorporating pressure communication into models for the elastic wave velocities of porous rocks: Connecting the borehole to laboratory measurements SPWLA 34nd Annual Logging Symposium Endres, A. L., Knight, R. J. 1993: 1–16
  • A model for incorporating surface phenomena into the dielectric response of a heterogeneous medium Journal of Colloid and Interface Science Endres, A. L., Knight, R. J. 1993; 157: 418-425
  • The use of nuclear magnetic resonance for studying and detecting hydrocarbon contaminants in porous rocks Water Resources Research Hedberg, S. A., Knight, R. J., MacKay, A. L., Whittall, K. P. 1993; 29: 1163-1170
  • Processing ground penetrating radar to improve resolution of near-surface targets Symposium on the Application of Geophysics to Environmental and Engineering Problems Gerlitz, K., Knoll, M. D., Cross, G. M., Luzitano, R. D., Knight, R. 1993
  • SEISMIC AND ELECTRICAL-PROPERTIES OF SANDSTONES AT LOW SATURATIONS JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH Knight, R., Dvorkin, J. 1992; 97 (B12): 17425-17432

    View details for Web of Science ID A1992JY18900013

  • A THEORETICAL TREATMENT OF THE EFFECT OF MICROSCOPIC FLUID DISTRIBUTION ON THE DIELECTRIC-PROPERTIES OF PARTIALLY SATURATED ROCKS GEOPHYSICAL PROSPECTING Endres, A. L., Knight, R. 1992; 40 (3): 307-324

    View details for Web of Science ID A1992JD89800003

  • A theoretical assessment of the effect of microscopic fluid distribution on the dielectric response of partially saturated rocks Geophysical Prospecting Endres, A. L., Knight, R. J. 1992; 40: 307-324
  • THE EFFECTS OF PORE-SCALE FLUID DISTRIBUTION ON THE PHYSICAL-PROPERTIES OF PARTIALLY SATURATED TIGHT SANDSTONES JOURNAL OF APPLIED PHYSICS Endres, A. L., Knight, R. 1991; 69 (2): 1091-1098

    View details for Web of Science ID A1991EU22500088

  • Hysteresis in the electrical resistivity of partially saturated sandstones Geophysics Knight, R. 1991; 56: 2139-2147
  • The effect of saturation history on electrical measurements Knight, R. J. 1991
  • Surface conduction at the hydrocarbon/water interface SPWLA 32nd Annual Logging Symposium Knight, R. J., Endres, A. 1991: 1–10
  • The characterization of pore geometry with nuclear magnetic resonance Canadian Well Logging Society Symposium Chapman, A., Knight, R. J. 1991
  • The effects of pore scale fluid distribution on the physical properties of partially saturated tight sandstones Journal of Applied Physics Endres, A. L., Knight, R. J. 1991; 69: 1091-1098
  • Characterization of a sand and gravel aquifer using ground penetrating radar, Cape Cod, Massachusetts USGS Toxic Substances Hydrology Technical Meeting Knoll, M., Haeni, P., Knight, R. J. 1991
  • A LABORATORY STUDY OF THE DEPENDENCE OF ELASTIC WAVE VELOCITIES ON PORE SCALE FLUID DISTRIBUTION GEOPHYSICAL RESEARCH LETTERS Knight, R., NOLENHOEKSEMA, R. 1990; 17 (10): 1529-1532

    View details for Web of Science ID A1990EA42800015

  • NUMERICAL MODELING OF MICROSCOPIC FLUID DISTRIBUTION IN POROUS-MEDIA JOURNAL OF APPLIED PHYSICS Knight, R., Chapman, A., Knoll, M. 1990; 68 (3): 994-1001

    View details for Web of Science ID A1990DP61600014

  • A NEW CONCEPT IN MODELING THE DIELECTRIC RESPONSE OF SANDSTONES - DEFINING A WETTED ROCK AND BULK WATER-SYSTEM GEOPHYSICS Knight, R., Endres, A. 1990; 55 (5): 586-594

    View details for Web of Science ID A1990DD74500009

  • Laboratory study of the dependence of acoustic properties on microscopic fluid distribution Society of Professional Well Log Analysts 31st Annual Logging Symposium Knight, R. J., Nolen-Hoeksema, R. A. 1990: 1–9
  • Hysteresis in the dielectric response of partially saturated sandstones: The importance of microscopic fluid distribution Society of Professional Well Log Analysts 31st Annual Logging Symposium Endres, A., Knight, R. J. 1990: 1–23
  • A laboratory study of the effect of pore scale fluid distribution on elastic wave velocities Geophysical Research Letters Knight, R. J., Nolen-Hoeksema, R. 1990; 17: 1529-1532
  • A new concept in modeling the dielectric response of sandstones: Defining a wetted rock and bulk water system Geophysics Knight, R. J., Endres, A. 1990; 55: 586-594
  • The effect of rock/water interaction in modelling the dielectric response of sandstones Society of Professional Well Log Analysts 30th Annual Logging Symposium Knight, R. J., Endres, A. 1989: 1–20
  • The effect of microscopic fluid distribution on elastic wave velocities 30th Annual Logging Symposium Endres, A., Knight, R. J. 1989: 20
  • The effect of microscopic fluid distribution on elastic wave velocities The Log Analyst Endres, A., Knight, R. J. 1989; 30: 437-445
  • THE DIELECTRIC-CONSTANT OF SANDSTONES, 60 KHZ TO 4 MHZ GEOPHYSICS Knight, R. J., Nur, A. 1987; 52 (5): 644-654

    View details for Web of Science ID A1987H195900004

  • Geometrical effects in the dielectric response of partially saturated sandstones The Log Analyst Knight, R. J., Nur, A. 1987; 28: 513-519
  • Dielectric enhancement due to the presence of thin gas pockets Society of Professional Well Log Analysts Twenty Seventh Annual Logging Symposium Knight, R. J., Nur, A. 1986: 1–11
  • Modeling the electrical response of sandstones with an equivalent electrical circuit Society of Professional Well Log Analysts Twenty Sixth Annual Logging Symposium Knight, R. J., Nur, A., Raistrick, I. D. 1985: 1–17
  • The effect of surface area to volume ratio on the dielectric response of sandstones The Physics and Chemistry of Composite Media, Electrochemical Society of America Proceedings Knight, R. J., Nur, A. 1985; 85: 336-345
  • The effect of level of water saturation on the dielectric constant of sandstones Society of Professional Well Log Analysts Twenty Fifth Annual Logging Symposium Knight, R. J., Nur, A. 1984: 1–16
  • THE USE OF COMPLEX-PLANE PLOTS IN STUDYING THE ELECTRICAL RESPONSE OF ROCKS JOURNAL OF GEOMAGNETISM AND GEOELECTRICITY Knight, R. J. 1983; 35 (11-1): 767-776

    View details for Web of Science ID A1983TK54200029

  • K Ar and fission track geochronometry of an Eocene thermal event in the Kettle River (West Half) Map Area, Southern British Columbia: Discussion Canadian Journal of Earth Sciences Farrar, E., Knight, R. J. 1975; 13: 182-183