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 elevation grid was used to quantify across the MAP region 1) the occurrence and thickness of surficial (< 15 meter (m) depth) confining material, 2) the top and bottom elevation corresponding to the surficial confining material, and 3) a metric representing the degree of surface confinement or connectivity that ranges from fully confining conditions to high potential hydrologic connectivity. These products were generated using the updated 12-class facies classifications of the 3D electrical resistivity model. See child item “Mississippi Alluvial Plain (MAP): Electrical Resistivity & Facies Classification Grids” for more details on the facies classes: https://www.sciencebase.gov/catalog/item/5f03a7bc82ce0afb2446e11f. The final surfaces and hydrogeologic metrics were exported as raster images in Georeferenced Tagged Image File Format (GeoTIFF) format. 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. 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.

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. To calculate estimates of streambed properties across the MAP region, e.g. the relative connection potential between streams and the adjacent Mississippi River Valley Alluvial aquifer (MRVA), new 3D grids of electrical resistivity were generated for 2 meter (m) depth layers and only shallow depths (0-30 m). One grid was made with the horizontal dimension aligning with the 1 kilometer (km) x 1 km National Hydrogeologic Grid (NHG; Clark et al. 2018), and a second version was generated at a finer resolution of 100 m x 100 m, subdividing the NHG grid. Stream locations taken from the National Hydrograph Dataset Plus (NHDPlus) high resolution dataset were buffered with a 1.0 km radius and then intersected with both shallow 3D depth grids to isolate resistivity values immediately beneath or adjacent to streams. Twelve “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). The potential hydraulic connection through streambed sediments was estimated by calculating the vertically integrated electrical conductance (VIC) across each 2 m layer between 0 and 10 m depth. The shallow 3D resistivity and facies grids were exported in NetCDF format with an accompanying XML NetCDF Markdown Language metadata file. The streambed connectivity estimates were exported as raster images in Georeferenced Tagged Image File Format (GeoTIFF). 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.

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. To calculate estimates of streambed properties across the MAP region, e.g. the relative connection potential between streams and the adjacent Mississippi River Valley Alluvial aquifer (MRVA), new 3D grids of electrical resistivity were generated for 2 meter (m) depth layers and only shallow depths (0-30 m). One grid was made with the horizontal dimension aligning with the 1 kilometer (km) x 1 km National Hydrogeologic Grid (NHG; Clark et al. 2018), and a second version was generated at a finer resolution of 100 m x 100 m, subdividing the NHG grid. Stream locations taken from the National Hydrograph Dataset Plus (NHDPlus) high resolution dataset were buffered with a 1.0 km radius and then intersected with both shallow 3D depth grids to isolate resistivity values immediately beneath or adjacent to streams. Twelve “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). The potential hydraulic connection through streambed sediments was estimated by calculating the vertically integrated electrical conductance (VIC) across each 2 m layer between 0 and 10 m depth. The shallow 3D resistivity and facies grids were exported in NetCDF format with an accompanying XML NetCDF Markdown Language metadata file. The streambed connectivity estimates were exported as raster images in Georeferenced Tagged Image File Format (GeoTIFF). 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.

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.

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.

Electrical resistivity results from two regional airborne electromagnetic (AEM) surveys (Minsley et al. 2021, and Burton et al. 2021) over the Mississippi Alluvial Plain (MAP) were combined by the U.S. Geological Survey to produce three-dimensional (3D) gridded models and derivative hydrogeologic products. First, the base of the Mississippi River Valley Alluvial aquifer (MRVA) was updated using the AEM resistivity data, both borehole and manual picks, and a supervised machine learning algorithm. The 3D resistivity elevation grid was then intersected with the 2018 potentiometric surface and the new base of MRVA surface to isolate the saturated MRVA extent and generate estimates of the hydrogeologic framework and properties. The saturated aquifer thickness was calculated as the difference between the potentiometric surface elevation and the MRVA base elevation. The average electrical resistivity and facies classification of the saturated aquifer material were calculated for each 1 kilometer (km) x 1 km grid cell. See child item “Mississippi Alluvial Plain: Electrical Resistivity & Facies Classification Grids” for more details on the facies classes. Lastly, the degree of connectivity across the base of the MRVA, i.e. how likely the MRVA is hydraulically connected to deeper subcropping Tertiary units, was estimated through the vertically integrated electrical conductance (VIC) between different vertical offsets (+/- 5 meter (m), 10 m, 25 m) from the aquifer base. For example, for every 1 km x 1 km cell, the VIC for +/- 25 m is the result of integrating the electrical conductance values from all 5 m elevation layers between 25 above the MRVA base and 25 m below the MRVA base. Areas with high VIC values suggest there is low or minimal hydraulic connection across the MRVA base, while low VIC values indicate areas of high potential connection. All products were exported as raster images in Georeferenced Tagged Image File Format (GeoTIFF) files. 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. 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.

Electrical resistivity results from two regional airborne electromagnetic (AEM) surveys (Minsley et al. 2021, and Burton et al. 2021) over the Mississippi Alluvial Plain (MAP) were combined by the U.S. Geological Survey to produce three-dimensional (3D) gridded models and derivative hydrogeologic products. First, the base of the Mississippi River Valley Alluvial aquifer (MRVA) was updated using the AEM resistivity data, both borehole and manual picks, and a supervised machine learning algorithm. The 3D resistivity elevation grid was then intersected with the 2018 potentiometric surface and the new base of MRVA surface to isolate the saturated MRVA extent and generate estimates of the hydrogeologic framework and properties. The saturated aquifer thickness was calculated as the difference between the potentiometric surface elevation and the MRVA base elevation. The average electrical resistivity and facies classification of the saturated aquifer material were calculated for each 1 kilometer (km) x 1 km grid cell. See child item “Mississippi Alluvial Plain: Electrical Resistivity & Facies Classification Grids” for more details on the facies classes. Lastly, the degree of connectivity across the base of the MRVA, i.e. how likely the MRVA is hydraulically connected to deeper subcropping Tertiary units, was estimated through the vertically integrated electrical conductance (VIC) between different vertical offsets (+/- 5 meter (m), 10 m, 25 m) from the aquifer base. For example, for every 1 km x 1 km cell, the VIC for +/- 25 m is the result of integrating the electrical conductance values from all 5 m elevation layers between 25 above the MRVA base and 25 m below the MRVA base. Areas with high VIC values suggest there is low or minimal hydraulic connection across the MRVA base, while low VIC values indicate areas of high potential connection. All products were exported as raster images in Georeferenced Tagged Image File Format (GeoTIFF) files. 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. 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.

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 minimally processed (raw) AEM data as supplied by CGG Canada Services, Ltd. (https://www.sciencebase.gov/catalog/item/5f4e951882ce4c3d1233cb7d), the fully processed (downsampled by averaging) sounding data (https://www.sciencebase.gov/catalog/item/5f4e953482ce4c3d1233cb82), and inverted resistivity depth sections along all flight lines (https://www.sciencebase.gov/catalog/item/5f4e954682ce4c3d1233cb84), as well as unprocessed and processed (following International Atomic Energy Agency Technical Report procedures) radiometric data as supplied by CGG Canada Services, Ltd. (https://www.sciencebase.gov/catalog/item/5f4e951882ce4c3d1233cb7d). Data acquisition and minimal processing was conducted by CGG Canada Services, Ltd. and described in detail in the contractor's report. 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 minimally processed (raw) AEM data as supplied by CGG Canada Services, Ltd. (https://www.sciencebase.gov/catalog/item/5f4e951882ce4c3d1233cb7d), the fully processed (downsampled by averaging) sounding data (https://www.sciencebase.gov/catalog/item/5f4e953482ce4c3d1233cb82), and inverted resistivity depth sections along all flight lines (https://www.sciencebase.gov/catalog/item/5f4e954682ce4c3d1233cb84), as well as unprocessed and processed (following International Atomic Energy Agency Technical Report procedures) radiometric data as supplied by CGG Canada Services, Ltd. (https://www.sciencebase.gov/catalog/item/5f4e951882ce4c3d1233cb7d). Data acquisition and minimal processing was conducted by CGG Canada Services, Ltd. and described in detail in the contractor's report. 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.

Electrical resistivity results from four regional airborne electromagnetic (AEM) surveys (Burton et al. 2024, Hoogenboom et al. 2023, Minsley et al. 2021 and Burton et al. 2021) over the Mississippi Alluvial Plain (MAP) were combined by the U.S. Geological Survey to produce three-dimensional (3D) gridded models and derivative hydrogeologic products. These products were first published using data from the first 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 subsequent AEM surveys, labeled with the year “2022” (Burton et al. 2024, Hoogenboom et al. 2023). 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. To support hydrogeologic and geologic studies within the MAP region and the Mississippi River Valley Alluvial aquifer (MRVA), derivative products were calculated from the 3D resistivity grids to refine system-scale detail of MRVA properties, the degree of confinement or connectivity in surface material, shallow streambed properties, and the hydrologic connection potential across the base of the MRVA. The 3D gridded models were exported in NetCDF format with accompanying XML NetCDF Markdown Language metadata files. All other products are provided as raster images in Georeferenced Tagged Image File Format (GeoTIFF) files. 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.M., 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.