Shallow soil characteristics were mapped near Shellmound, Mississippi, using the DualEM 421 electromagnetic sensor in October 2018. Data were acquired by towing the DualEM sensor on a wheeled cart behind an ATV, with the sensor at a height of 0.432 meters (m) above the ground surface. Approximately 175 line-kilometers of data were acquired over an area of nearly four square kilometers, with 25 m separation between survey lines. Data were manually edited for noise sources such as powerlines or other buried structures, and averaged to regular output soundings every 5 m along survey lines. This data release contains the processed data that have been averaged and culled to produce final resistivity models. Digital data of the processed soundings are provided and fields are defined in the data dictionary.

Shallow soil characteristics were mapped near Shellmound, Mississippi, using the DualEM 421 electromagnetic sensor in October 2018. Data were acquired by towing the DualEM sensor on a wheeled cart behind an all-terrain vehicle (ATV), with the sensor at a height of 0.432 meters (m) above the ground surface. Approximately 175 line-kilometers of data were acquired over an area of nearly four square-kilometers, with 25 m separation between survey lines. Data were manually edited for noise sources such as powerlines or other buried structures and averaged to regular output soundings every 5 m along survey lines. The processed data were inverted to recover models of electrical resistivity structure as a function of depth at each sounding location using a spatially constrained inversion. This data release contains the raw and processed data, as well as inverted resistivity models. Model results show typical depth of investigation from about 4 – 6 m, with spatial variability in mapped electrical resistivity characteristic of fluvial deposition of sediments in channels and scroll bar features adjacent to the Tallahatchie River and nearby abandoned meander channels.

Shallow soil characteristics were mapped near Shellmound, Mississippi, using the DualEM 421 electromagnetic sensor in October 2018. Data were acquired by towing the DualEM sensor on a wheeled cart behind an all-terrain vehicle (ATV), with the sensor at a height of 0.432 meters (m) above the ground surface. Approximately 175 line-kilometers of data were acquired over an area of nearly four square-kilometers, with 25 m separation between survey lines. Data were manually edited for noise sources such as powerlines or other buried structures and averaged to regular output soundings every 5 m along survey lines. The processed data were inverted to recover models of electrical resistivity structure as a function of depth at each sounding location using a spatially constrained inversion. This data release contains the raw and processed data, as well as inverted resistivity models. Model results show typical depth of investigation from about 4 – 6 m, with spatial variability in mapped electrical resistivity characteristic of fluvial deposition of sediments in channels and scroll bar features adjacent to the Tallahatchie River and nearby abandoned meander channels.

Shallow soil characteristics were mapped near Shellmound, Mississippi, using the DualEM 421 electromagnetic sensor in October 2018. Data were acquired by towing the DualEM sensor on a wheeled cart behind an ATV, with the sensor at a height of 0.432 meters (m) above the ground surface. Approximately 175 line-kilometers of data were acquired over an area of nearly four square kilometers, with 25 m separation between survey lines. Raw data are provided here.

The bulk electrical conductivity of the subsurface was indirectly measured with electromagnetic imaging (EMI) by using induced secondary electromagnetic signals generated by subsurface electrical conductors in response to transmitted electromagnetic energy (Zohdy and others, 1974). Electromagnetic induction data were collected using a DUALEM-421 (DualEM, Inc.) mounted on an inflatable stand-up paddle board about 15 centimeters above the water surface. The DUALEM-421 uses 3 transmitter-receiver coil spacings (4-, 2-, and 1-meters) and 2 orientations (vertical dipole, and horizontal dipole). Larger coil spacings interrogate a larger/deeper sampling volume than smaller coil separations. REFERENCE: U.S. Geological Survey, Techniques of Water-Resources Investigations, Book 2, Chapter D1, Zhody, A. A. R., Eaton , G. P., and Mabey, D. R. https://doi.org/10.3133/twri02D1

The bulk electrical conductivity of the subsurface was indirectly measured with electromagnetic imaging (EMI) by using induced secondary electromagnetic signals generated by subsurface electrical conductors in response to transmitted electromagnetic energy (Zohdy and others, 1974). Electromagnetic induction data were collected using a DUALEM-421 (DualEM, Inc.) mounted on an inflatable stand-up paddle board about 15 centimeters above the water surface. The DUALEM-421 uses 3 transmitter-receiver coil spacings (4-, 2-, and 1-meters) and 2 orientations (vertical dipole, and horizontal dipole). Larger coil spacings interrogate a larger/deeper sampling volume than smaller coil separations. REFERENCE: U.S. Geological Survey, Techniques of Water-Resources Investigations, Book 2, Chapter D1, Zhody, A. A. R., Eaton , G. P., and Mabey, D. R. https://doi.org/10.3133/twri02D1

Airborne electromagnetic (AEM), magnetic, and radiometric data were acquired in late February to early March 2018 along 2,364 line-kilometers in the Shellmound, Mississippi study area. Data were acquired by CGG Canada Services, Ltd. with three different helicopter-borne sensors: the CGG Canada Services, Ltd. RESOLVE frequency-domain AEM instrument that is used to map subsurface geologic structure at depths up to 100 meters, depending on the subsurface resistivity; a Scintrex CS-3 cesium vapor magnetometer that detects changes in deep (hundreds of meters to kilometers) geologic structure based on variations in the magnetic properties of different formations; and a Radiation Solutions RS-500 spectrometer that detects the abundance of natural radioelements potassium, uranium, and thorium in the upper 20-30 cm that is used to determine differences in soil constituents. The survey was flown at a nominal sensor flight height of 30 m above terrain to form block-style coverage with 250 to 1,000-meter spaced east-west flight lines. This data release includes minimally processed (raw) AEM data as supplied by CGG Canada Services, Ltd. (https://www.sciencebase.gov/catalog/item/5ca6ce7ee4b0c3b0064c2ce5), the fully processed (averaged and culled) sounding data (https://www.sciencebase.gov/catalog/item/5d0814b9e4b0e3d3115bdab6), and laterally constrained inverted resistivity depth sections along all flight lines (https://www.sciencebase.gov/catalog/item/5ca6a4e6e4b0c3b0064c2c2b), as well as unprocessed and processed (diurnally corrected and draped to terrain) magnetic data (https://www.sciencebase.gov/catalog/item/5ca6ce7ee4b0c3b0064c2ce5), and unprocessed and processed (following International Atomic Energy Agency Technical Report procedures) radiometric data (https://www.sciencebase.gov/catalog/item/5ca6ce7ee4b0c3b0064c2ce5). Data acquisition and minimal processing were conducted by CGG Canada Services, Ltd. and described in detail in the contractor's report. Digital data from production flights are provided, and data fields are defined in the data dictionary. A total field magnetic anomaly grid and a ternary radiometric image are provided as well (https://www.sciencebase.gov/catalog/item/5cd0ad9de4b09b8c0b79a53f). An important driver for this survey is a managed aquifer recharge pilot project developed by the U.S. Department of Agriculture Agricultural Research Service investigating the use of bank filtration along the Tallahatchie River as a source for recharge in areas of significant groundwater decline by direct injection into the Mississippi River Valley Alluvial Aquifer (MRVA). Understanding the structure of the aquifer, including both shallow and deep confining units, is important for the success of this pilot engineering study and will be even more important for potential future large-scale engineering projects and groundwater model development efforts. REFERENCES International Atomic Energy Agency, 1991, Airborne Gamma Ray Spectrometer Surveying, Technical Reports Series No. 323, IAEA, Vienna. U.S. Geological Survey, The National Map, 2017, 3DEP products and services: The National Map, 3D Elevation Program Web page, accessed October 2018 at https://nationalmap.gov/3DEP/3dep_prodserv.html.

In June 2018, the U.S. Geological Survey (USGS) in cooperation with the U.S. Environmental Protection Agency (EPA) collected geophysical measurements to help evaluate the suitability of a proposed landfill site for disposing mine-waste materials in Fredericktown, Missouri. Geophysical methods were used to evaluate and characterize the unconsolidated sediment (i.e., regolith) above the crystalline bedrock as well as determine depth bedrock. Land-based geophysical methods included frequency domain electromagnetic induction (FDEM), electrical resistivity tomography (ERT), horizontal-to-vertical spectral ratio passive seismic (HVSR), and shear-wave seismic refraction. Water-borne methods included FDEM surveys to characterize the Fredericktown City Lake sediments as well as forward-looking infrared (FLIR) imagery taken along the City Lake shoreline to identify locations of potential groundwater-surface water interactions.

In June 2018, the U.S. Geological Survey (USGS) in cooperation with the U.S. Environmental Protection Agency (EPA) collected geophysical measurements to help evaluate the suitability of a proposed landfill site for disposing mine-waste materials in Fredericktown, Missouri. Geophysical methods were used to evaluate and characterize the unconsolidated sediment (i.e., regolith) above the crystalline bedrock as well as determine depth bedrock. Land-based geophysical methods included frequency domain electromagnetic induction (FDEM), electrical resistivity tomography (ERT), horizontal-to-vertical spectral ratio passive seismic (HVSR), and shear-wave seismic refraction. Water-borne methods included FDEM surveys to characterize the Fredericktown City Lake sediments as well as forward-looking infrared (FLIR) imagery taken along the City Lake shoreline to identify locations of potential groundwater-surface water interactions.

Airborne frequency domain electromagnetic (AEM) data were acquired in a grid pattern consisting of many west-east oriented survey lines over the Tallahatchie River during November 2018. Data were collected by members of the U.S. Geological Survey, Crustal Geophysics and Geochemistry Science Center Group, and CGG. AEM data acquired in Leflore County, Mississippi, were collected to characterize the subsurface resistivity structure in support of a U.S. Geological Survey groundwater investigation of the Mississippi Alluvial Plain. Airborne EM data were acquired with the Resolve (CGG Airborne) frequency-domain instrument over the same reach 18 line-kilometers that follow the Tallahatchie River in Leflore County in Mississippi as part of a mapping campaign in the Mississippi alluvial plain region. The AEM data comprise five horizontal coplanar transmitter-receiver (Tx-Rx) coil pairs separated by about 7.9 meters (m) at frequencies between 383 and 133,528 Hertz (Hz), and one vertical coaxial coil pair separated by about 9 m that operates at 3,315 Hz. Nominal system height above ground, or river, surface was 30 m and was recorded along flight paths. Data along the survey line that were used to produce the final resistivity models are provided here. Digital data of the processed soundings are provided, and fields are defined in a data dictionary. (1) File: MAPRegAEM2018_EM_Mag_Rad_rawData_L8072002.csv is comma-delimited ASCII file that contain the least processed data. Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (2) File: MAPRegAEM2018_ProcessedData_L8072002.csv is comma- delimited ASCII file containing the processed data . Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (3) File: MAPRegAEM2018_ResistivityModels_L8072002.csv is comma-delimited ASCII files containing the inversion model results. Model locations are provided as UTM Zone 15 N projection and datum of WGS-84. (4) File: 20181115_ShellmoundMS_AEM_LINE120_INVERTED_image.png and 20181115_ShellmoundMS_AEM_LINE120_INVERTED_image.pdf are the inverted model output as a 2D profile of electrical resistivity distribution in the subsurface.