Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, Mississippi Embayment, and Gulf Coastal Plain, September 2021 - January 2022

Airborne electromagnetic (AEM), magnetic, and radiometric data were acquired September 2021 to January 2022 along 27,204 line-kilometers (line-km) over the Mississippi Alluvial Plain (MAP), Mississippi Embayment, and Gulf Coastal Plain. Data were acquired by Xcalibur Multiphysics (Canada), Ltd. with three different airborne sensors: the 30Hz 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 300 and 600 km (nominal) spaced east-west flight lines. The main survey block covers 24,654 line-km. The Chicot aquifer focus area was surveyed along 360 line-km (flight numbers 2900101-2900421 nonsuccessive). The Mississippi River and the Atchafalaya River were surveyed along their center axes, covering 742 line-km (flight line numbers 6004001-6004003 and 5002001-5002002). Two separate inset grids were flown: (1) University of Memphis (UMemphis) focus area lines with 500 m line spacing for a total of 1260 line-km (flight line numbers 1000301-1030001 nonsuccessive), and (2) Hot Springs focus area with 350 m line spacing for a total of 188 line-km (flight line numbers 2001001-2027001 nonsuccessive). 91-series lines are repeat test-lines flown periodically throughout the survey, with one repeat line established for each base station. 901- and 904-series lines are flown under standard survey conditions with the transmitter on and the receiver off to evaluate the noise contribution from the acquisition system pre- and post- flight, respectively. 902- and 905-series lines are ~60 second high-altitude datasets collected to evaluate the system out of ground-response pre- and post- flight, respectively. 903-series lines are 30-40 second 'swoop' datasets to confirm correct operation of the system during variable pitch manoeuvres. 906-series lines are flown under standard survey conditions with the transmitter off and the receiver on to evaluate the ambient noise in the system. AEM data were inverted using 1-D inversion to produce models of electrical resistivity along flight paths.