Steven M Smith
Steven Smith is a Geologist with the Geology, Geophysics, and Geochemistry Science Center.
Science and Products
National Geochemical Database
The National Geochemical Database project assembles, reformats, corrects, and archives historical data obtained from the geochemical analysis of millions of geologic samples collected for USGS studies. These data, representing hundreds of millions of dollars' worth of USGS research, are provided to USGS researchers; other Federal agencies; State Geological Surveys and Environmental Protection...
Legacy Geochemical Data from Hardcopy Records of Selected Past U.S. Geological Survey Projects
This data release contains geochemical data from selected U.S. Geological Survey (USGS) projects from the 1960s-1980s that were previously unpublished as digital data. The objective of those projects was to describe the geology, determine petrologic and geochemical characteristics, or to evaluate the mineral resource potential of Federal Lands and adjacent study areas. These data comprise geochemi
Geochemical data generated by projects funded by the USGS Earth Mapping Resources Initiative (ver. 10.0, June 2024)
The geochemical data included here were generated as part of the Earth Mapping Resources Initiative (Earth MRI), which was developed by the U.S. Geological Survey (USGS) in response to a Federal directive calling on various Federal agencies to address potential vulnerabilities in the Nation’s supply of critical mineral resources. Earth MRI is a partnership between the USGS, State Geological Survey
Reanalysis of Selected Archived NURE-HSSR Sediment and Soil Samples from Arizona, California, Idaho, Montana, Nevada, New Mexico, and Utah
Beginning in November of 2015, the U.S. Geological Survey (USGS) undertook a project to reanalyze approximately 60,000 archived sample splits collected as part of the National Uranium Resource Evaluation (NURE) Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) project from selected areas in Arizona, California, Idaho, Montana, Nevada, New Mexico, and Utah. A small amount (approximately 0.
Reanalysis of Additional Selected Archived NURE-HSSR Sediment Samples from Idaho and Montana
In December of 2018, the U.S. Geological Survey (USGS) signed a Technical Assistance Agreement with a third party to reanalyze 2,324 archived sample splits collected as part of the National Uranium Resource Evaluation (NURE) Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) project from selected areas in Idaho and Montana. A small amount (approximately 0.25 grams [g]) of sieved less than
Reanalysis of Selected Archived NURE-HSSR Sediment and Soil Samples from Alaska
Selected archived sample splits collected as part of the National Uranium Resource Evaluation (NURE) Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) program, were reanalyzed by the U.S. Geological Survey (USGS) as part of a NURE-HSSR Reanalysis project (Smith and others, 2018). A small amount (approximately 0.25 grams [g]) of sieved less than 75-micron sample material was retrieved from
Geochemical Data Release for Gospel-Hump Wilderness Area, Magruder Corridor and Special Mining Management Zone Additions to the Frank Church River of No Return Wilderness Area, and adjacent areas Idaho and Montana
The data release for Gospel-Hump Wilderness Area and the Magruder Corridor and Special Mining Management Zone Additions to the Frank Church River of No Return Wilderness Area, and adjacent areas Idaho and Montana, contains a subset of previously unpublished geochemical data from the 1979-1984 projects. In the case of Gospel-Hump Wilderness Area study (Lund and Esparza, 1990), the purpose of the pr
Locatable Mineral Assessment Tracts for the U.S. Geological Survey Sagebrush Mineral Resource Assessment Project
The polygon (vector) feature class represents locatable mineral resource assessment tracts (tracts of land) associated with the Department of the Interior (DOI) Sagebrush Focal Areas in Montana, Wyoming and Utah, central Idaho, and the Oregon-Nevada-Idaho border area. The mineral resources tracts are geographic areas that were assessed by the U.S. Geological Survey (USGS) and were determined to be
Filter Total Items: 21
Data release of reprocessed select National Uranium Resources Evaluation program samples in Wyoming
The U.S. Atomic Energy Commission established the National Uranium Resources Evaluation (NURE) program in 1973 to identify uranium resources throughout the United States. Part of this program focused on the collection of stream-sediment samples and subsequent geochemical analyses of these samples for uranium, in addition to 47 other elements. As part of the original program, 18,424 stream-sediment
Authors
David W. Lucke, Steven M. Smith, Jaime S. Azain, Andrew David Ingraham
Geology and mineral resources of the North-Central Montana Sagebrush Focal Area: Chapter D in Mineral resources of the Sagebrush Focal Areas of Idaho, Montana, Nevada, Oregon, Utah, and Wyoming
SummaryThe U.S. Department of the Interior has proposed to withdraw approximately 10 million acres of Federal lands from mineral entry (subject to valid existing rights) from 12 million acres of lands defined as Sagebrush Focal Areas (SFAs) in Idaho, Montana, Nevada, Oregon, Utah, and Wyoming (for further discussion on the lands involved see Scientific Investigations Report 2016–5089–A). The purpo
Authors
Jeffrey L. Mauk, Michael L. Zientek, B. Carter Hearn, Heather L. Parks, M. Christopher Jenkins, Eric D. Anderson, Mary Ellen Benson, Donald I. Bleiwas, Jacob DeAngelo, Paul Denning, Connie L. Dicken, Ronald M. Drake, Gregory L. Fernette, Helen W. Folger, Stuart A. Giles, Jonathan M. G. Glen, Matthew Granitto, Jon E. Haacke, John D. Horton, Karen D. Kelley, Joyce A. Ober, Barnaby W. Rockwell, Carma A. San Juan, Elizabeth S. Sangine, Peter N. Schweitzer, Brian N. Shaffer, Steven M. Smith, Colin F. Williams, Douglas B. Yager
By
Energy and Minerals Mission Area, Energy Resources Program, Mineral Resources Program, National Laboratories Program, Science and Decisions Center, Geology, Energy & Minerals Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geology, Geophysics, and Geochemistry Science Center, National Minerals Information Center
Geology and mineral resources of the North-Central Idaho Sagebrush Focal Area: Chapter C in Mineral resources of the Sagebrush Focal Areas of Idaho, Montana, Nevada, Oregon, Utah, and Wyoming
SummaryThe U.S. Department of the Interior has proposed to withdraw approximately 10 million acres of Federal lands from mineral entry (subject to valid existing rights) from 12 million acres of lands defined as Sagebrush Focal Areas (SFAs) in Idaho, Montana, Nevada, Oregon, Utah, and Wyoming (for further discussion on the lands involved see Scientific Investigations Report 2016–5089–A). The purpo
Authors
Karen Lund, Lukas Zürcher, Albert H. Hofstra, Bradley S. Van Gosen, Mary Ellen Benson, Stephen E. Box, Eric D. Anderson, Donald I. Bleiwas, Jacob DeAngelo, Ronald M. Drake, Gregory L. Fernette, Stuart A. Giles, Jonathan M. G. Glen, Jon E. Haacke, John D. Horton, David A. John, Gilpin R. Robinson, Barnaby W. Rockwell, Carma A. San Juan, Brian N. Shaffer, Steven M. Smith, Colin F. Williams
By
Energy and Minerals Mission Area, Energy Resources Program, Mineral Resources Program, National Laboratories Program, Science and Decisions Center, Geology, Energy & Minerals Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geology, Geophysics, and Geochemistry Science Center, National Minerals Information Center
First steps of integrated spatial modeling of titanium, zirconium, and rare earth element resources within the Coastal Plain sediments of the southeastern United States
The Coastal Plain of the southeastern United States has extensive, unconsolidated sedimentary deposits that are enriched in heavy minerals containing titanium, zirconium, and rare earth element resources. Areas favorable for exploration and development of these resources are being identified by geochemical data, which are supplemented with geological, geophysical, hydrological, and geographical da
Authors
Karl J. Ellefsen, Bradley S. Van Gosen, David L. Fey, James R. Budahn, Steven M. Smith, Anjana K. Shah
Levelling and merging of two discrete national-scale geochemical databases: A case study showing the surficial expression of metalliferous black shales
Government-sponsored, national-scale, soil and sediment geochemical databases are used to estimate regional and local background concentrations for environmental issues, identify possible anthropogenic contamination, estimate mineral endowment, explore for new mineral deposits, evaluate nutrient levels for agriculture, and establish concentration relationships with human or animal health. Because
Authors
Steven M. Smith, Ryan T. Neilson, Stuart A. Giles
Database creation, data quality assessment, and geochemical maps (phase V, deliverable 59)—Final report on compilation and validation of geochemical data
Under the World Bank-funded Second Projet de Renforcement Institutionnel du Secteur Minier de la Republique Islamique de Mauritanie (PRISM-II), this Phase V geochemistry report follows earlier Phase I and Phase II summary reports on geochemical data (U.S. Geological Survey, 2007 and Eppinger, 2007; respectively). All the reports are based on evaluations of geochemical data collected in 1999-2004 u
Authors
Robert G. Eppinger, Stuart A. Giles, Gregory K. Lee, Steven M. Smith
History and evaluation of national-scale geochemical data sets for the United States
Six national-scale, or near national-scale, geochemical data sets for soils or stream sediments exist for the United States. The earliest of these, here termed the ‘Shacklette’ data set, was generated by a U.S. Geological Survey (USGS) project conducted from 1961 to 1975. This project used soil collected from a depth of about 20 cm as the sampling medium at 1323 sites throughout the conterminous U
Authors
David B. Smith, Steven M. Smith, John D. Horton
An exploration hydrogeochemical study at the giant Pebble porphyry Cu-Au-Mo deposit, Alaska, USA, using high-resolution ICP-MS
A hydrogeochemical study using high resolution ICP-MS was undertaken at the giant Pebble porphyry Cu-Au-Mo deposit and surrounding mineral occurrences. Surface water and groundwater samples from regional background and the deposit area were collected at 168 sites. Rigorous quality control reveals impressive results at low nanogram per litre (ng/l) levels. Sites with pH values below 5.1 are from po
Authors
Robert G. Eppinger, David L. Fey, Stuart A. Giles, Karen D. Kelley, Steven M. Smith
Porphyry Cu indicator minerals in till as an exploration tool: Example from the giant Pebble porphyry Cu-Au-Mo deposit, Alaska, USA
Porphyry Cu indicator minerals are mineral species in clastic sediments that indicate the presence of mineralization and hydrothermal alteration associated with porphyry Cu and associated skarn deposits. Porphyry Cu indicator minerals recovered from shallow till samples near the giant Pebble Cu-Au-Mo porphyry deposit in SW Alaska, USA, include apatite, andradite garnet, Mn-epidote, visible gold, j
Authors
Karen D. Kelley, Robert G. Eppinger, J. Lang, Steven M. Smith, David L. Fey
USGS exploration geochemistry studies at the Pebble porphyry Cu-Au-Mo deposit, Alaska— Pdf of presentation
From 2007 through 2010, scientists in the U.S. Geological Survey (USGS) have been conducting exploration-oriented geochemical and geophysical studies in the region surrounding the giant Pebble porphyry Cu-Au-Mo deposit in southwestern Alaska. The Cretaceous Pebble deposit is concealed under tundra, glacial till, and Tertiary cover rocks, and is undisturbed except for numerous exploration drill hol
Authors
Robert G. Eppinger, Karen D. Kelley, David L. Fey, Stuart A. Giles, Burke J. Minsley, Steven M. Smith
Geochemical data for samples collected in 2008 near the concealed pebble porphyry Cu-Au-Mo deposit, Southwest Alaska
In the summer of 2007, the U.S. Geological Survey (USGS) began an exploration geochemical research study over the Pebble porphyry copper-gold-molybdenum deposit. This report presents the analytical data collected in 2008. The Pebble deposit is world class in size, and is almost entirely concealed by tundra, glacial deposits, and post-Cretaceous volcanic rocks. The Pebble deposit was chosen for thi
Authors
David L. Fey, Matthew Granitto, Stuart A. Giles, Steven M. Smith, Robert G. Eppinger, Karen D. Kelley
An orientation soil survey at the Pebble Cu-Au-Mo porphyry deposit, Alaska
Soil samples were collected in 2007 and 2008 along three traverses across the giant Pebble Cu-Au-Mo porphyry deposit. Within each soil pit, four subsamples were collected following recommended protocols for each of ten commonly-used and proprietary leach/digestion techniques. The significance of geochemical patterns generated by these techniques was classified by visual inspection of plots showing
Authors
Steven M. Smith, Robert G. Eppinger, David L. Fey, Karen D. Kelley, S. A. Giles
Science and Products
National Geochemical Database
The National Geochemical Database project assembles, reformats, corrects, and archives historical data obtained from the geochemical analysis of millions of geologic samples collected for USGS studies. These data, representing hundreds of millions of dollars' worth of USGS research, are provided to USGS researchers; other Federal agencies; State Geological Surveys and Environmental Protection...
Legacy Geochemical Data from Hardcopy Records of Selected Past U.S. Geological Survey Projects
This data release contains geochemical data from selected U.S. Geological Survey (USGS) projects from the 1960s-1980s that were previously unpublished as digital data. The objective of those projects was to describe the geology, determine petrologic and geochemical characteristics, or to evaluate the mineral resource potential of Federal Lands and adjacent study areas. These data comprise geochemi
Geochemical data generated by projects funded by the USGS Earth Mapping Resources Initiative (ver. 10.0, June 2024)
The geochemical data included here were generated as part of the Earth Mapping Resources Initiative (Earth MRI), which was developed by the U.S. Geological Survey (USGS) in response to a Federal directive calling on various Federal agencies to address potential vulnerabilities in the Nation’s supply of critical mineral resources. Earth MRI is a partnership between the USGS, State Geological Survey
Reanalysis of Selected Archived NURE-HSSR Sediment and Soil Samples from Arizona, California, Idaho, Montana, Nevada, New Mexico, and Utah
Beginning in November of 2015, the U.S. Geological Survey (USGS) undertook a project to reanalyze approximately 60,000 archived sample splits collected as part of the National Uranium Resource Evaluation (NURE) Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) project from selected areas in Arizona, California, Idaho, Montana, Nevada, New Mexico, and Utah. A small amount (approximately 0.
Reanalysis of Additional Selected Archived NURE-HSSR Sediment Samples from Idaho and Montana
In December of 2018, the U.S. Geological Survey (USGS) signed a Technical Assistance Agreement with a third party to reanalyze 2,324 archived sample splits collected as part of the National Uranium Resource Evaluation (NURE) Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) project from selected areas in Idaho and Montana. A small amount (approximately 0.25 grams [g]) of sieved less than
Reanalysis of Selected Archived NURE-HSSR Sediment and Soil Samples from Alaska
Selected archived sample splits collected as part of the National Uranium Resource Evaluation (NURE) Hydrogeochemical and Stream Sediment Reconnaissance (HSSR) program, were reanalyzed by the U.S. Geological Survey (USGS) as part of a NURE-HSSR Reanalysis project (Smith and others, 2018). A small amount (approximately 0.25 grams [g]) of sieved less than 75-micron sample material was retrieved from
Geochemical Data Release for Gospel-Hump Wilderness Area, Magruder Corridor and Special Mining Management Zone Additions to the Frank Church River of No Return Wilderness Area, and adjacent areas Idaho and Montana
The data release for Gospel-Hump Wilderness Area and the Magruder Corridor and Special Mining Management Zone Additions to the Frank Church River of No Return Wilderness Area, and adjacent areas Idaho and Montana, contains a subset of previously unpublished geochemical data from the 1979-1984 projects. In the case of Gospel-Hump Wilderness Area study (Lund and Esparza, 1990), the purpose of the pr
Locatable Mineral Assessment Tracts for the U.S. Geological Survey Sagebrush Mineral Resource Assessment Project
The polygon (vector) feature class represents locatable mineral resource assessment tracts (tracts of land) associated with the Department of the Interior (DOI) Sagebrush Focal Areas in Montana, Wyoming and Utah, central Idaho, and the Oregon-Nevada-Idaho border area. The mineral resources tracts are geographic areas that were assessed by the U.S. Geological Survey (USGS) and were determined to be
Filter Total Items: 21
Data release of reprocessed select National Uranium Resources Evaluation program samples in Wyoming
The U.S. Atomic Energy Commission established the National Uranium Resources Evaluation (NURE) program in 1973 to identify uranium resources throughout the United States. Part of this program focused on the collection of stream-sediment samples and subsequent geochemical analyses of these samples for uranium, in addition to 47 other elements. As part of the original program, 18,424 stream-sediment
Authors
David W. Lucke, Steven M. Smith, Jaime S. Azain, Andrew David Ingraham
Geology and mineral resources of the North-Central Montana Sagebrush Focal Area: Chapter D in Mineral resources of the Sagebrush Focal Areas of Idaho, Montana, Nevada, Oregon, Utah, and Wyoming
SummaryThe U.S. Department of the Interior has proposed to withdraw approximately 10 million acres of Federal lands from mineral entry (subject to valid existing rights) from 12 million acres of lands defined as Sagebrush Focal Areas (SFAs) in Idaho, Montana, Nevada, Oregon, Utah, and Wyoming (for further discussion on the lands involved see Scientific Investigations Report 2016–5089–A). The purpo
Authors
Jeffrey L. Mauk, Michael L. Zientek, B. Carter Hearn, Heather L. Parks, M. Christopher Jenkins, Eric D. Anderson, Mary Ellen Benson, Donald I. Bleiwas, Jacob DeAngelo, Paul Denning, Connie L. Dicken, Ronald M. Drake, Gregory L. Fernette, Helen W. Folger, Stuart A. Giles, Jonathan M. G. Glen, Matthew Granitto, Jon E. Haacke, John D. Horton, Karen D. Kelley, Joyce A. Ober, Barnaby W. Rockwell, Carma A. San Juan, Elizabeth S. Sangine, Peter N. Schweitzer, Brian N. Shaffer, Steven M. Smith, Colin F. Williams, Douglas B. Yager
By
Energy and Minerals Mission Area, Energy Resources Program, Mineral Resources Program, National Laboratories Program, Science and Decisions Center, Geology, Energy & Minerals Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geology, Geophysics, and Geochemistry Science Center, National Minerals Information Center
Geology and mineral resources of the North-Central Idaho Sagebrush Focal Area: Chapter C in Mineral resources of the Sagebrush Focal Areas of Idaho, Montana, Nevada, Oregon, Utah, and Wyoming
SummaryThe U.S. Department of the Interior has proposed to withdraw approximately 10 million acres of Federal lands from mineral entry (subject to valid existing rights) from 12 million acres of lands defined as Sagebrush Focal Areas (SFAs) in Idaho, Montana, Nevada, Oregon, Utah, and Wyoming (for further discussion on the lands involved see Scientific Investigations Report 2016–5089–A). The purpo
Authors
Karen Lund, Lukas Zürcher, Albert H. Hofstra, Bradley S. Van Gosen, Mary Ellen Benson, Stephen E. Box, Eric D. Anderson, Donald I. Bleiwas, Jacob DeAngelo, Ronald M. Drake, Gregory L. Fernette, Stuart A. Giles, Jonathan M. G. Glen, Jon E. Haacke, John D. Horton, David A. John, Gilpin R. Robinson, Barnaby W. Rockwell, Carma A. San Juan, Brian N. Shaffer, Steven M. Smith, Colin F. Williams
By
Energy and Minerals Mission Area, Energy Resources Program, Mineral Resources Program, National Laboratories Program, Science and Decisions Center, Geology, Energy & Minerals Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Geology, Geophysics, and Geochemistry Science Center, National Minerals Information Center
First steps of integrated spatial modeling of titanium, zirconium, and rare earth element resources within the Coastal Plain sediments of the southeastern United States
The Coastal Plain of the southeastern United States has extensive, unconsolidated sedimentary deposits that are enriched in heavy minerals containing titanium, zirconium, and rare earth element resources. Areas favorable for exploration and development of these resources are being identified by geochemical data, which are supplemented with geological, geophysical, hydrological, and geographical da
Authors
Karl J. Ellefsen, Bradley S. Van Gosen, David L. Fey, James R. Budahn, Steven M. Smith, Anjana K. Shah
Levelling and merging of two discrete national-scale geochemical databases: A case study showing the surficial expression of metalliferous black shales
Government-sponsored, national-scale, soil and sediment geochemical databases are used to estimate regional and local background concentrations for environmental issues, identify possible anthropogenic contamination, estimate mineral endowment, explore for new mineral deposits, evaluate nutrient levels for agriculture, and establish concentration relationships with human or animal health. Because
Authors
Steven M. Smith, Ryan T. Neilson, Stuart A. Giles
Database creation, data quality assessment, and geochemical maps (phase V, deliverable 59)—Final report on compilation and validation of geochemical data
Under the World Bank-funded Second Projet de Renforcement Institutionnel du Secteur Minier de la Republique Islamique de Mauritanie (PRISM-II), this Phase V geochemistry report follows earlier Phase I and Phase II summary reports on geochemical data (U.S. Geological Survey, 2007 and Eppinger, 2007; respectively). All the reports are based on evaluations of geochemical data collected in 1999-2004 u
Authors
Robert G. Eppinger, Stuart A. Giles, Gregory K. Lee, Steven M. Smith
History and evaluation of national-scale geochemical data sets for the United States
Six national-scale, or near national-scale, geochemical data sets for soils or stream sediments exist for the United States. The earliest of these, here termed the ‘Shacklette’ data set, was generated by a U.S. Geological Survey (USGS) project conducted from 1961 to 1975. This project used soil collected from a depth of about 20 cm as the sampling medium at 1323 sites throughout the conterminous U
Authors
David B. Smith, Steven M. Smith, John D. Horton
An exploration hydrogeochemical study at the giant Pebble porphyry Cu-Au-Mo deposit, Alaska, USA, using high-resolution ICP-MS
A hydrogeochemical study using high resolution ICP-MS was undertaken at the giant Pebble porphyry Cu-Au-Mo deposit and surrounding mineral occurrences. Surface water and groundwater samples from regional background and the deposit area were collected at 168 sites. Rigorous quality control reveals impressive results at low nanogram per litre (ng/l) levels. Sites with pH values below 5.1 are from po
Authors
Robert G. Eppinger, David L. Fey, Stuart A. Giles, Karen D. Kelley, Steven M. Smith
Porphyry Cu indicator minerals in till as an exploration tool: Example from the giant Pebble porphyry Cu-Au-Mo deposit, Alaska, USA
Porphyry Cu indicator minerals are mineral species in clastic sediments that indicate the presence of mineralization and hydrothermal alteration associated with porphyry Cu and associated skarn deposits. Porphyry Cu indicator minerals recovered from shallow till samples near the giant Pebble Cu-Au-Mo porphyry deposit in SW Alaska, USA, include apatite, andradite garnet, Mn-epidote, visible gold, j
Authors
Karen D. Kelley, Robert G. Eppinger, J. Lang, Steven M. Smith, David L. Fey
USGS exploration geochemistry studies at the Pebble porphyry Cu-Au-Mo deposit, Alaska— Pdf of presentation
From 2007 through 2010, scientists in the U.S. Geological Survey (USGS) have been conducting exploration-oriented geochemical and geophysical studies in the region surrounding the giant Pebble porphyry Cu-Au-Mo deposit in southwestern Alaska. The Cretaceous Pebble deposit is concealed under tundra, glacial till, and Tertiary cover rocks, and is undisturbed except for numerous exploration drill hol
Authors
Robert G. Eppinger, Karen D. Kelley, David L. Fey, Stuart A. Giles, Burke J. Minsley, Steven M. Smith
Geochemical data for samples collected in 2008 near the concealed pebble porphyry Cu-Au-Mo deposit, Southwest Alaska
In the summer of 2007, the U.S. Geological Survey (USGS) began an exploration geochemical research study over the Pebble porphyry copper-gold-molybdenum deposit. This report presents the analytical data collected in 2008. The Pebble deposit is world class in size, and is almost entirely concealed by tundra, glacial deposits, and post-Cretaceous volcanic rocks. The Pebble deposit was chosen for thi
Authors
David L. Fey, Matthew Granitto, Stuart A. Giles, Steven M. Smith, Robert G. Eppinger, Karen D. Kelley
An orientation soil survey at the Pebble Cu-Au-Mo porphyry deposit, Alaska
Soil samples were collected in 2007 and 2008 along three traverses across the giant Pebble Cu-Au-Mo porphyry deposit. Within each soil pit, four subsamples were collected following recommended protocols for each of ten commonly-used and proprietary leach/digestion techniques. The significance of geochemical patterns generated by these techniques was classified by visual inspection of plots showing
Authors
Steven M. Smith, Robert G. Eppinger, David L. Fey, Karen D. Kelley, S. A. Giles