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.

2021年9月至2022年1月期间，研究团队沿27204测线公里的航迹，在密西西比河冲积平原（Mississippi Alluvial Plain，MAP）、密西西比河沿岸凹陷区以及墨西哥湾沿岸平原采集了航空电磁（Airborne Electromagnetic，AEM）、磁法与放射性测量数据。本次数据由加拿大Xcalibur Multiphysics有限公司使用三款不同的航空传感器采集：其一为30Hz TEMPEST时域航空电磁仪器，可依据地下电阻率情况，绘制深度可达300米的地下地质构造图；其二为Scintrex CS-3型铯蒸气磁强计，可通过不同地层的磁性差异，探测深部（数百米至千米级）地质构造变化；其三为Radiation Solutions RS-500型光谱仪，可探测地表20-30厘米深度内天然放射性元素钾、铀、钍的含量，以此分析土壤组分差异。本次航测的传感器标称飞行高度为距地表120米，测线呈东西走向，标称间距分别为300千米与600千米。主测区覆盖测线总长24654测线公里。奇科特含水层重点区域的航测总长为360测线公里（飞行编号：2900101-2900421，非连续测线）。密西西比河与阿查法拉亚河的航测沿河道中轴线开展，覆盖总长742测线公里（飞行测线编号：6004001-6004003与5002001-5002002）。本次航测还布设了两处独立的补充测区：(1) 孟菲斯大学（University of Memphis，简称UMemphis）重点区域测区，测线间距500米，总长1260测线公里（飞行测线编号：1000301-1030001，非连续测线）；(2) 温泉重点区域测区，测线间距350米，总长188测线公里（飞行测线编号：2001001-2027001，非连续测线）。91系列测线为全航测周期内定期布设的重复测试测线，每个基站对应一条重复测线。901系列与904系列测线分别在航测前后，于标准航测条件下开展（发射机开启、接收机关闭），用于评估采集系统的噪声贡献。902系列与905系列测线分别在航测前后采集时长约60秒的高空数据集，用于评估系统的离地响应情况。903系列测线为时长30-40秒的‘俯冲’数据集，用于验证系统在变俯仰机动过程中的运行状态是否正常。906系列测线于标准航测条件下开展（发射机关闭、接收机开启），用于评估系统的环境噪声水平。本次航空电磁数据采用一维反演方法进行处理，生成沿飞行路径的电阻率模型。