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.

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 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.

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.

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.

Towed transient electromagnetic (tTEM) data were acquired adjacent to the Tallahatchie River during March 2018. During the survey, approximately 35 line-kilometers were collected in the Shellmound, Mississippi study area. Data were collected by members of the U.S. Geological Survey, Hydrogeophysics Branch, and the Aarhus University HydroGeophysics Group. FloaTEM data acquired near the Tallahatchie River in Leflore County, in Mississippi, were collected to characterize the subsurface resistivity structure in support of a U.S. Geological Survey groundwater investigation of the Mississippi Alluvial Plain. tTEM data were collected using an Aarhus University HydroGeophysics Group tTEM unit using a transmitter loop (Tx) size, 4 by 2 meter square (m^2), in an offset-loop receiver (Rx) configuration utilizing a receiver coil that is 0.5 by 0.5 m^2 in size (with an effective area of 35 m^2) towed about 7 meters behind the Tx loop. The Tx loop was towed about 2.8m behind the all-terrain vehicle (ATV) The Tx outputs dual currents of about 3 and 30 amperes (A) for dual-moment transmission. The measurement cycles take approximately 0.5 seconds to complete and are comprised of several hundred individual transients that are averaged into 1D soundings along the profile. This data release includes the averaged, culled, and inverted tTEM data along the survey line that were used to produce the final resistivity models. Digital data of the processed soundings are provided, and fields are defined in a data dictionary. (1) Files with *AVERAGED.xyz and *AVERAGED.csv are space- and comma-delimited ASCII files that contain the least processed data where transients were averaged together and most coupled data were removed. Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (2) Files with *CULLED.xyz and *CULLED.csv are space- and comma- delimited ASCII files containing the processed data where negatively-impacted transients and coupled data were removed using a combination of automated and manual processing. Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (3) Files with *INVERTED.xyz and *INVERTED.csv are space- and 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) Files with *INVERTED_image.png and *INVERTED_image.pdf are the inverted model output as a 2D profile of electrical resistivity distribution in the subsurface.

Towed transient electromagnetic (tTEM) data were acquired adjacent to the Tallahatchie River during March 2018. During the survey, approximately 35 line-kilometers were collected in the Shellmound, Mississippi study area. Data were collected by members of the U.S. Geological Survey, Hydrogeophysics Branch, and the Aarhus University HydroGeophysics Group. FloaTEM data acquired near the Tallahatchie River in Leflore County, in Mississippi, were collected to characterize the subsurface resistivity structure in support of a U.S. Geological Survey groundwater investigation of the Mississippi Alluvial Plain. tTEM data were collected using an Aarhus University HydroGeophysics Group tTEM unit using a transmitter loop (Tx) size, 4 by 2 meter square (m^2), in an offset-loop receiver (Rx) configuration utilizing a receiver coil that is 0.5 by 0.5 m^2 in size (with an effective area of 35 m^2) towed about 7 meters behind the Tx loop. The Tx loop was towed about 2.8m behind the all-terrain vehicle (ATV) The Tx outputs dual currents of about 3 and 30 amperes (A) for dual-moment transmission. The measurement cycles take approximately 0.5 seconds to complete and are comprised of several hundred individual transients that are averaged into 1D soundings along the profile. This data release includes the averaged, culled, and inverted tTEM data along the survey line that were used to produce the final resistivity models. Digital data of the processed soundings are provided, and fields are defined in a data dictionary. (1) Files with *AVERAGED.xyz and *AVERAGED.csv are space- and comma-delimited ASCII files that contain the least processed data where transients were averaged together and most coupled data were removed. Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (2) Files with *CULLED.xyz and *CULLED.csv are space- and comma- delimited ASCII files containing the processed data where negatively-impacted transients and coupled data were removed using a combination of automated and manual processing. Data locations are provided as UTM Zone 15 N projection and datum of WGS-84. (3) Files with *INVERTED.xyz and *INVERTED.csv are space- and 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) Files with *INVERTED_image.png and *INVERTED_image.pdf are the inverted model output as a 2D profile of electrical resistivity distribution in the subsurface.

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 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 inverted resistivity models. Digital data of the laterally constrained inversions are provided and fields are defined in the data dictionary. 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.