The Mississippi Alluvial Plain (MAP) Project contains several geologic units which act as important aquifers. We collected several sets of time-domain electromagnetic (TEM) data consisting of two higher-density surveys and six regional-scale transects. The higher density surveys were collected to compare and contrast to other geophysical data not included in this data release, such as airborne electromagnetic, magnetic resonance sounding, and towed time-domain electromagnetic surveys . The transects, which were collected over the span of three years, cross the MAP study area from east-to-west, with about 100 km line spacing, and cover an area of nearly 100,000 square-kilometer. Each transect spans a distance of 100-200 km, with 10-20 TEM soundings that capture the major geologic units. TEM is capable of measuring the electrical resistivity structure of the subsurface and distinguishing between geologic units that possess different electrical properties. These TEM data are being used to refine the 3D Mississippi Embayment Aquifer System Regional Groundwater Availability Study (https://www2.usgs.gov/water/lowermississippigulf/lmgweb/meras/index.html).

Airborne electromagnetic (AEM), magnetic, and radiometric data were acquired November 2019 to March 2020 along 24,030 line-kilometers (line-km) over the Mississippi Alluvial Plain (MAP). Data were acquired by CGG Canada Services, Ltd. with three different airborne sensors: the CGG Canada Services, Ltd. TEMPEST time-domain AEM instrument that is used to map subsurface geologic structure at depths up to 300 meters (m), 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 centimeters that is used to determine differences in soil constituents. The survey was flown at a nominal sensor flight height of 120 m above terrain with 6-kilometer spaced east-west flight lines. The main survey block covers 22,250 line-km. The Mississippi River and the Arkansas River were surveyed along their center axes, covering 1,225 line-km (flight line numbers 500101 and 700201-700206 nonsuccessive), and three separate inset grids were flown: (1) Ozark basement reconnaissance lines with variable line spacing for a total of 234 line-km (flight line numbers 400801-401401 nonsuccessive), (2) Shellmound focus area in Mississippi with 250 m line spacing for a total of 485 line-km (flight line numbers 604501-608101 nonsuccessive), and (3) New Madrid Seismic Zone focus area in Missouri and Tennessee with variable line spacing for a total of 161 line-km (flight line numbers 710101-710401 nonsuccessive). 91-series lines are repeat test-lines flown periodically throughout the survey, with one repeat line established for each base station. 902- and 905-series lines are ~60 second high-altitude datasets collected pre- and post- flight, respectively, to evaluate the system out of ground-response. This data release includes inverted depth sections along all flight lines from the AEM data (https://www.sciencebase.gov/catalog/item/5f4e954682ce4c3d1233cb84). Digital data from production flights are provided in ASEG-GDF2 format, an ASCII format geophysical data standard that uses a self-describing collection of files to allow data to be automatically identified and read by a computer application. Data fields in the data file (.DAT) are defined in the associated definition file (.DFN). Please see the ReadME included in this data release for a description of how to interpret the .DFN files or visit https://www.aseg.org.au/sites/default/files/pdf/ASEG-GDF2-REV4.pdf for more information on the ASEG-GDF2 standard.

Airborne electromagnetic (AEM), magnetic, and radiometric data were acquired November 2019 to March 2020 along 24,030 line-kilometers (line-km) over the Mississippi Alluvial Plain (MAP). Data were acquired by CGG Canada Services, Ltd. with three different airborne sensors: the CGG Canada Services, Ltd. TEMPEST time-domain AEM instrument that is used to map subsurface geologic structure at depths up to 300 meters (m), 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 centimeters that is used to determine differences in soil constituents. The survey was flown at a nominal sensor flight height of 120 m above terrain with 6-kilometer spaced east-west flight lines. The main survey block covers 22,250 line-km. The Mississippi River and the Arkansas River were surveyed along their center axes, covering 1,225 line-km (flight line numbers 500101 and 700201-700206 nonsuccessive), and three separate inset grids were flown: (1) Ozark basement reconnaissance lines with variable line spacing for a total of 234 line-km (flight line numbers 400801-401401 nonsuccessive), (2) Shellmound focus area in Mississippi with 250 m line spacing for a total of 485 line-km (flight line numbers 604501-608101 nonsuccessive), and (3) New Madrid Seismic Zone focus area in Missouri and Tennessee with variable line spacing for a total of 161 line-km (flight line numbers 710101-710401 nonsuccessive). 91-series lines are repeat test-lines flown periodically throughout the survey, with one repeat line established for each base station. 902- and 905-series lines are ~60 second high-altitude datasets collected pre- and post- flight, respectively, to evaluate the system out of ground-response. This data release includes inverted depth sections along all flight lines from the AEM data (https://www.sciencebase.gov/catalog/item/5f4e954682ce4c3d1233cb84). Digital data from production flights are provided in ASEG-GDF2 format, an ASCII format geophysical data standard that uses a self-describing collection of files to allow data to be automatically identified and read by a computer application. Data fields in the data file (.DAT) are defined in the associated definition file (.DFN). Please see the ReadME included in this data release for a description of how to interpret the .DFN files or visit https://www.aseg.org.au/sites/default/files/pdf/ASEG-GDF2-REV4.pdf for more information on the ASEG-GDF2 standard.

Airborne electromagnetic (AEM), magnetic, and radiometric data were acquired November 2019 to March 2020 along 24,030 line-kilometers (line-km) over the Mississippi Alluvial Plain (MAP). Data were acquired by CGG Canada Services, Ltd. with three different airborne sensors: the CGG Canada Services, Ltd. TEMPEST time-domain AEM instrument that is used to map subsurface geologic structure at depths up to 300 meters (m), 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 centimeters that is used to determine differences in soil constituents. The survey was flown at a nominal sensor flight height of 120 m above terrain with 6-kilometer spaced east-west flight lines. The main survey block covers 22,250 line-km. The Mississippi River and the Arkansas River were surveyed along their center axes, covering 1,225 line-km (flight line numbers 500101 and 700201-700206 nonsuccessive), and three separate inset grids were flown: (1) Ozark basement reconnaissance lines with variable line spacing for a total of 234 line-km (flight line numbers 400801-401401 nonsuccessive), (2) Shellmound focus area in Mississippi with 250 m line spacing for a total of 485 line-km (flight line numbers 604501-608101 nonsuccessive), and (3) New Madrid Seismic Zone focus area in Missouri and Tennessee with variable line spacing for a total of 161 line-km (flight line numbers 710101-710401 nonsuccessive). 91-series lines are repeat test-lines flown periodically throughout the survey, with one repeat line established for each base station. 902- and 905-series lines are ~60 second high-altitude datasets collected pre- and post- flight, respectively, to evaluate the system out of ground-response. This data release includes inverted depth sections along all flight lines from the AEM data (https://www.sciencebase.gov/catalog/item/5f4e954682ce4c3d1233cb84). Digital data from production flights are provided in ASEG-GDF2 format, an ASCII format geophysical data standard that uses a self-describing collection of files to allow data to be automatically identified and read by a computer application. Data fields in the data file (.DAT) are defined in the associated definition file (.DFN). Please see the ReadME included in this data release for a description of how to interpret the .DFN files or visit https://www.aseg.org.au/sites/default/files/pdf/ASEG-GDF2-REV4.pdf for more information on the ASEG-GDF2 standard.

Airborne electromagnetic (AEM), magnetic, and radiometric data were acquired November 2018 to February 2019 along 16,816 line-kilometers (line-km) over the Mississippi Alluvial Plain (MAP). 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 with 6- to 12-kilometer spaced east-west flight lines. The main survey block covers 13,641 line-km, including two north-south tie lines extending the length of the survey. Several rivers were surveyed along their center axes, covering 2,640 line-km (flight line numbers 8010000-8100001 nonsuccessive), and two separate inset grids were flown: (1) Crowley's Ridge in Arkansas with 1.5-km spaced east-west flights for a total of 406 line-km (flight line numbers 24025-24477 nonsuccessive) and (2) University of Memphis focus area in Tennessee with variable line spacing for a total of 129 line-km (flight line numbers 30010-30060 and 39010-39050 nonsuccessive). This data release includes laterally-constrained inverted depth sections along all flight lines from the AEM data. Digital data of the laterally constrained inversions are provided and fields are defined in the data dictionary (https://www.sciencebase.gov/catalog/item/5d76ba5ce4b0c4f70d01ff94).

Airborne electromagnetic (AEM), magnetic, and radiometric data were acquired November 2018 to February 2019 along 16,816 line-kilometers (line-km) over the Mississippi Alluvial Plain (MAP). 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 with 6- to 12-kilometer spaced east-west flight lines. The main survey block covers 13,641 line-km, including two north-south tie lines extending the length of the survey. Several rivers were surveyed along their center axes, covering 2,640 line-km (flight line numbers 8010000-8100001 nonsuccessive), and two separate inset grids were flown: (1) Crowley's Ridge in Arkansas with 1.5-km spaced east-west flights for a total of 406 line-km (flight line numbers 24025-24477 nonsuccessive) and (2) University of Memphis focus area in Tennessee with variable line spacing for a total of 129 line-km (flight line numbers 30010-30060 and 39010-39050 nonsuccessive). This data release includes laterally-constrained inverted depth sections along all flight lines from the AEM data. Digital data of the laterally constrained inversions are provided and fields are defined in the data dictionary (https://www.sciencebase.gov/catalog/item/5d76ba5ce4b0c4f70d01ff94).

Airborne electromagnetic (AEM), magnetic, and radiometric data were acquired May 25 through August 7, 2021 along 10,706 line-kilometers (line-km) over the Mississippi Alluvial Plain (MAP). Data were acquired by Xcalibur Multiphysics with three different helicopter-borne sensors: the Xcalibur Multiphysics 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. Sixteen rivers were surveyed along their center axes, covering 3,467 line-km. Ten rivers are within the surficial Mississippi River Alluvial aquifer boundary: Black River, White River, Big Sunflower River, Little Sunflower River, Ouachita River, Tensas River, Obion River, Saline River, Little Red River, and Bogue Phalia. Six rivers are within the Chicot aquifer boundary: Vermillion River, Bayou Teche, Mermentau River, Calcasieu River, Sabine River, and Bayou Lacassine. Select levee reaches were surveyed along the Mississippi and Arkansas Rivers along the riverside toe, landside toe, and 91m landward offset from the landside toe for a total of 5,896 line-km. Four grids were flown over gravel bars in the Mississippi River: Prairie Point block, Island 63 block, Crumrod block, White River block, and three short segments along the Mississippi River targeting gravel bars. Three additional grids were flown: (1) Melton site in Mississippi with 100-m spaced north-south flight lines for a total of 23 line-km, (2) optically stimulated luminescence (OSL) core study site in Arkansas with 500m east-west line spacing for a total of 268 line-km, and (3) Raccourci Lake in Louisiana with variable flight lines for a total of 100 line-km. Additional detail on flight line numbers is included in the supplemental section. Also included is a small levee dataset acquired in March 2018 near Greenville, Mississippi during the Shellmound AEM survey https://www.sciencebase.gov/catalog/item/5c9e6c42e4b0b8a7f62f5da6. This dataset does not contain magnetic and radiometric data. The survey includes four lines parallel to and over the levee for a total of 27 line-km. This data release includes laterally-constrained inverted depth sections along all flight lines from the AEM data. Digital data of the laterally constrained inversions are provided and fields are defined in the data dictionary https://www.sciencebase.gov/catalog/item/5d76ba5ce4b0c4f70d01ff94.

Airborne electromagnetic (AEM), magnetic, and radiometric data were acquired May 25 through August 7, 2021 along 10,706 line-kilometers (line-km) over the Mississippi Alluvial Plain (MAP). Data were acquired by Xcalibur Multiphysics with three different helicopter-borne sensors: the Xcalibur Multiphysics 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. Sixteen rivers were surveyed along their center axes, covering 3,467 line-km. Ten rivers are within the surficial Mississippi River Alluvial aquifer boundary: Black River, White River, Big Sunflower River, Little Sunflower River, Ouachita River, Tensas River, Obion River, Saline River, Little Red River, and Bogue Phalia. Six rivers are within the Chicot aquifer boundary: Vermillion River, Bayou Teche, Mermentau River, Calcasieu River, Sabine River, and Bayou Lacassine. Select levee reaches were surveyed along the Mississippi and Arkansas Rivers along the riverside toe, landside toe, and 91m landward offset from the landside toe for a total of 5,896 line-km. Four grids were flown over gravel bars in the Mississippi River: Prairie Point block, Island 63 block, Crumrod block, White River block, and three short segments along the Mississippi River targeting gravel bars. Three additional grids were flown: (1) Melton site in Mississippi with 100-m spaced north-south flight lines for a total of 23 line-km, (2) optically stimulated luminescence (OSL) core study site in Arkansas with 500m east-west line spacing for a total of 268 line-km, and (3) Raccourci Lake in Louisiana with variable flight lines for a total of 100 line-km. Additional detail on flight line numbers is included in the supplemental section. Also included is a small levee dataset acquired in March 2018 near Greenville, Mississippi during the Shellmound AEM survey https://www.sciencebase.gov/catalog/item/5c9e6c42e4b0b8a7f62f5da6. This dataset does not contain magnetic and radiometric data. The survey includes four lines parallel to and over the levee for a total of 27 line-km. This data release includes laterally-constrained inverted depth sections along all flight lines from the AEM data. Digital data of the laterally constrained inversions are provided and fields are defined in the data dictionary https://www.sciencebase.gov/catalog/item/5d76ba5ce4b0c4f70d01ff94.

Airborne electromagnetic (AEM), magnetic, and radiometric data were acquired May 25 through August 7, 2021 along 10,706 line-kilometers (line-km) over the Mississippi Alluvial Plain (MAP). Data were acquired by Xcalibur Multiphysics with three different helicopter-borne sensors: the Xcalibur Multiphysics 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. Sixteen rivers were surveyed along their center axes, covering 3,467 line-km. Ten rivers are within the surficial Mississippi River Alluvial aquifer boundary: Black River, White River, Big Sunflower River, Little Sunflower River, Ouachita River, Tensas River, Obion River, Saline River, Little Red River, and Bogue Phalia. Six rivers are within the Chicot aquifer boundary: Vermillion River, Bayou Teche, Mermentau River, Calcasieu River, Sabine River, and Bayou Lacassine. Select levee reaches were surveyed along the Mississippi and Arkansas Rivers along the riverside toe, landside toe, and 91m landward offset from the landside toe for a total of 5,896 line-km. Four grids were flown over gravel bars in the Mississippi River: Prairie Point block, Island 63 block, Crumrod block, White River block, and three short segments along the Mississippi River targeting gravel bars. Three additional grids were flown: (1) Melton site in Mississippi with 100-m spaced north-south flight lines for a total of 23 line-km, (2) optically stimulated luminescence (OSL) core study site in Arkansas with 500m east-west line spacing for a total of 268 line-km, and (3) Raccourci Lake in Louisiana with variable flight lines for a total of 100 line-km. Additional detail on flight line numbers is included in the supplemental section. Also included is a small levee dataset acquired in March 2018 near Greenville, Mississippi during the Shellmound AEM survey https://www.sciencebase.gov/catalog/item/5c9e6c42e4b0b8a7f62f5da6. This dataset does not contain magnetic and radiometric data. The survey includes four lines parallel to and over the levee for a total of 27 line-km. This data release includes laterally-constrained inverted depth sections along all flight lines from the AEM data. Digital data of the laterally constrained inversions are provided and fields are defined in the data dictionary https://www.sciencebase.gov/catalog/item/5d76ba5ce4b0c4f70d01ff94.

Electrical resistivity results from four regional airborne electromagnetic (AEM) surveys (Burton et al. 2024, Hoogenboom et al. 2023, Minsley et al. 2021, Burton et al. 2021) over the Mississippi Alluvial Plain (MAP) were combined by the U.S. Geological Survey (USGS) to produce three-dimensional (3D) gridded models and derivative hydrogeologic products. The 3D models and products were first published using data from the earlier two AEM regional surveys, labeled with the year “2020” (Minsley et al. 2021, Burton et al. 2021). The 3D resistivity models and select derivative products were later updated by incorporating additional data from the two later AEM surveys, labeled with the year “2022” (Burton et al. 2024, Hoogenboom et al. 2023). In both 2020 and 2022 versions, grids were discretized in the horizontal dimension to align with the 1 kilometer (km) x 1 km National Hydrogeologic Grid (NHG; Clark et al. 2018), and vertically discretized into both 5 meter (m) depth slices and 5 m elevation slices. Facies classes were defined to categorize materials expected to have similar hydrologic and geologic properties based on their electrical resistivity (i.e. low classes correspond to clays and silts with low permeability, and higher classes reflect larger grain sizes (sands, gravels) with expected higher permeability). In the 2020 version, 10 facies classes were used, and classes were further separated based on position relative to the base of the Mississippi River Valley Alluvial aquifer (MRVA) to capture geologic distinctions in addition to hydrogeologic. In the 2022 version, two new facies classes were added to the lower resistivity end (12 classes total) and no distinction was made based on the MRVA extent. All 3D grids were exported into NetCDF format and all metadata from the NetCDF files are provided within the accompanying XML NetCDF Markdown Language file (*.ncml). Burton, B.L., Adams, R.F. Adams, Minsley, B.J., Pace, M.D.M., Kress, W.H., Rigby, J.R., and Bussell, A.M., 2024, Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, March 2018 and May - August 2021: U.S. Geological Survey data release, https://doi.org/10.5066/P9KPK3UJ. Hoogenboom, B.E., Minsley, B.J., James, S.R., and Pace, M.D., 2023, Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, Mississippi Embayment, and Gulf Coastal Plain, September 2021 - January 2022: U.S. Geological Survey data release, https://doi.org/10.5066/P93DO0EO. Burton, B.L., Minsley, B.J., Bloss, B.R., and Kress, W.H., 2021, Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, November 2018 - February 2019: U.S. Geological Survey data release, https://doi.org/10.5066/P9XBBBUU. Clark, B.R., Barlow, P.M., Peterson, S.M., Hughes, J.D., Reeves, H.W., and Viger, R.J., 2018, National-scale grid to support regional groundwater availability studies and a national hydrogeologic database: U.S. Geological Survey data release, https://doi.org/10.5066/F7P84B24. Minsley, B.J., James, S.R., Bedrosian, P.A., Pace, M.D., Hoogenboom, B.E., and Burton, B.L., 2021, Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, November 2019 - March 2020: U.S. Geological Survey data release, https://doi.org/10.5066/P9E44CTQ.