Airborne electromagnetic, magnetic, and radiometric survey of the Mississippi Alluvial Plain, November 2019 - March 2020

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., the fully processed (downsampled by averaging) sounding data, and inverted resistivity depth sections along all flight lines, as well as unprocessed and processed (following International Atomic Energy Agency Technical Report procedures) radiometric data as supplied by CGG Canada Services, Ltd. 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.

航空电磁（Airborne electromagnetic, AEM）、磁测与放射性测量数据采集于2019年11月至2020年3月，沿密西西比河冲积平原（Mississippi Alluvial Plain, MAP）布设了总计24030测线公里的测线。本次数据由CGG加拿大服务有限公司采集，使用了三款不同的航空传感器：其一为CGG加拿大服务有限公司的TEMPEST时域航空电磁仪器，可依据地下电阻率情况，在最大300米深度范围内绘制地下地质构造；其二为Scintrex CS-3铯蒸气磁力仪，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光谱仪，用于检测表层20-30厘米内天然放射性元素钾、铀、钍的丰度，以此判定土壤组分差异。
本次测量的标称传感器飞行高度为距地表120米，测线呈东西走向，线间距为6公里。主测区覆盖测线总长22250测线公里。沿密西西比河与阿肯色河的中心轴线开展了专项测量，覆盖测线总长1225测线公里（测线编号：500101，以及非连续的700201-700206）。此外还布设了三个独立的补充测区：（1）奥扎克基底踏勘测区，线间距可变，总测线长度234测线公里（测线编号：400801-401401，非连续）；（2）位于密西西比州的谢尔蒙德（Shellmound）重点区，线间距250米，总测线长度485测线公里（测线编号：604501-608101，非连续）；（3）位于密苏里州和田纳西州的新马德里地震带（New Madrid Seismic Zone）重点区，线间距可变，总测线长度161测线公里（测线编号：710101-710401，非连续）。
91系列测线为本次测量全程定期布设的重复测试线，每个基站对应设置一条重复测线。902与905系列测线分别为飞行前与飞行后采集的时长约60秒的高空数据集，用于评估系统的地面外响应。
本次公开的数据包含CGG加拿大服务有限公司提供的轻度处理（原始）航空电磁数据、经全流程处理（通过平均方式降采样）的测深数据，以及所有测线的反演电阻率深度剖面；同时包含CGG加拿大服务有限公司提供的未经处理与遵循国际原子能机构技术报告规程完成处理的放射性测量数据。数据采集与初步处理由CGG加拿大服务有限公司完成，详细说明参见承包商报告。
生产飞行获取的数字数据采用ASEG-GDF2格式存储，这是一种基于ASCII的地球物理数据标准，通过自描述文件集合实现计算机应用程序对数据的自动识别与读取。数据文件（.DAT）中的数据字段由对应的关联定义文件（.DFN）定义。请参阅本次数据发布中包含的ReadME文件以了解.DFN文件的解读方法，或访问https://www.aseg.org.au/sites/default/files/pdf/ASEG-GDF2-REV4.pdf 获取ASEG-GDF2标准的更多信息。