Airborne electromagnetic, magnetic, and radiometric surveys of the Mississippi Alluvial Plain and Chicot Aquifer System, March 2018 and May - August 2021

Airborne geophysical surveys were acquired in March 2018 and May 25 through August 7, 2021 using a helicopter-based platform. These surveys were collected along 10,706 line-kilometers (line-km) within selected areas of the Mississippi Alluvial Plain (MAP) and the Chicot Aquifer System in the southeastern United States. The airborne geophysical surveys include electromagnetic, magnetic, and radiometric sensor data collected in rivers and levees throughout the two areas to evaluate groundwater and surface-water interaction, riverine ecosystems, and infrastructure.

This data release contains three child items that provide:

Minimally processed (raw) data supplied by the airborne contractor (Xcalibur Multiphysics) for all three sensors along all flight lines: Airborne electromagnetic, magnetic, and radiometric surveys of the Mississippi Alluvial Plain and Chicot Aquifer System, March 2018 and May - August 2021: Raw Data
Fully processed electromagnetic data: Airborne electromagnetic, magnetic, and radiometric surveys of the Mississippi Alluvial Plain and Chicot Aquifer System, March 2018 and May - August 2021: Processed Data
Final inverted resistivity models: Airborne electromagnetic, magnetic, and radiometric surveys of the Mississippi Alluvial Plain and Chicot Aquifer System, March 2018 and May - August 2021: Resistivity Models

Supporting documentation contained in this data release include:

Contractor's report- Description of data acquisition and minimal processing as conducted by Xcalibur Multiphysics (Airborne Survey Contractor).

Organization:
The data files contained in this release are broken up according to the three main objectives of these surveys:  1) River surveys along the thalweg of major rivers within the MAP and the Chicot Aquifer extents; 2) Levee surveys along the Mississippi and Arkansas rivers from Cairo, IL to Baton Rouge, LA and northwest from the confluence of the Mississippi and Arkansas rivers to Pine Bluff, AR; and 3) Gridded products focused on gravel bars within the Mississippi River from Helena, MS to the confluence with the Arkansas River.

Data were collected on the following 16 rivers:

Rivers within the MAP boundary:  Black, White, Big Sunflower, Little Sunflower, Ouachita, Tensas, Obion, Saline, Little Red, and Bogue Phalia.
Rivers within the Chicot Aquifer extent:  Mermentau, Calcasieu, Sabine, Vermillion, Bayou Teche, and Bayou Lacassine.

Levee Surveys:
Along selected reaches of the Mississippi and Arkansas Rivers, levee survey lines were flown along the toe of the levee both on the side adjacent to the river and on the side opposite the river.  In addition, where possible, a third line was flown 91m (300 feet) offset from the toe of the levee opposite to the river. Additional processing was done on all levee lines and is described in the data dictionaries and processing step sections of the metadata included in the “Processed Data” and “Resistivity Models” child items of this data release.

Seven gridded surveys were also collected:

Mississippi River gravel bars: 

250 m Line Spacing

 Prairie Point
 Island 63
 Crumrod

100 m Line Spacing

White River

  Melton Grid:23 line-km at a 100 m line spacing over a site near Minter City, MS.
  AR OSL Grid: 268 line-km at a 500 m spacing over a series of the drill core locations near Paragould, AR.
  Raccourci Grid:100 line-km at variable spacings over Raccourci Old River, a relic oxbow near Batchelor, LA.

Additional Data:
A dataset collected on levees near Greenville, Mississippi, in March 2018 is also included in this data release.  The survey includes four lines parallel to and over the levee for a total of 27 line-km. This dataset was collected as an evaluation of the technical approach used on the more comprehensive surveys in the MAP and Chicot Aquifer extents. This dataset contains AEM data only (magnetic and radiometric data were not collected).

Additional details on flight line numbers and citations for the various methods used in the collection and processing of the radiometric data are included in the supplemental section.

航空地球物理测量于2018年3月，以及2021年5月25日至8月7日期间，采用直升机搭载平台开展。本次测量航线总长10706测线公里（line-km），覆盖美国东南部密西西比河冲积平原（Mississippi Alluvial Plain, MAP）与奇科特含水层系统（Chicot Aquifer System）的选定区域。本航空地球物理测量搭载电磁、磁法及放射性辐射传感器，在上述两处区域的河流与堤岸沿线采集数据，用于评估地下水与地表水交互作用、河流生态系统及基础设施状况。

本次数据发布包含三个子数据集，分别提供：
1. 航空承包商（Xcalibur Multiphysics）提供的全航线三种传感器原始数据，仅经过最低限度处理：《密西西比河冲积平原与奇科特含水层系统2018年3月及2021年5月—8月航空电磁、磁法及放射性测量原始数据》
2. 全流程处理后的电磁数据：《密西西比河冲积平原与奇科特含水层系统2018年3月及2021年5月—8月航空电磁、磁法及放射性测量处理后数据》
3. 最终反演电阻率模型：《密西西比河冲积平原与奇科特含水层系统2018年3月及2021年5月—8月航空电磁、磁法及放射性测量电阻率模型》

本数据发布附带的支撑文档包括：
承包商报告——由航空测量承包商Xcalibur Multiphysics编制的数据采集与初步处理说明。

数据集组织方式
本发布中的数据文件按照本次测量的三大核心目标进行分类：
1. 大型河流深泓线航道测量：覆盖密西西比河冲积平原与奇科特含水层范围内的主要河流主航道；
2. 堤岸测量：沿密西西比河与阿肯色河布设测线，范围从伊利诺伊州开罗至路易斯安那州巴吞鲁日，以及从密西西比河与阿肯色河汇流处西北延伸至阿肯色州派恩布拉夫；
3. 网格化产品：覆盖密西西比河从密西西比州海伦娜至阿肯色河汇流处范围内的砾石滩区域。

本次测量共覆盖以下16条河流：
密西西比河冲积平原范围内河流：布莱克河（Black）、怀特河（White）、大森弗劳尔河（Big Sunflower）、小森弗劳尔河（Little Sunflower）、沃希托河（Ouachita）、滕萨斯河（Tensas）、奥伯恩河（Obion）、萨林河（Saline）、小红河（Little Red）以及博格法利亚河（Bogue Phalia）。
奇科特含水层范围内河流：梅芒托河（Mermentau）、卡尔卡苏河（Calcasieu）、萨宾河（Sabine）、弗米利恩河（Vermillion）、特谢湾（Bayou Teche）以及拉卡辛湾（Bayou Lacassine）。

堤岸测量
在密西西比河与阿肯色河的选定河段，测量航线沿堤岸脚布设，分别覆盖临河侧与背河侧；在条件允许的区域，额外在背河侧距堤岸脚91米（300英尺）处布设第三条测线。所有堤岸测线均经过额外处理，相关说明详见本数据发布的“处理后数据”与“电阻率模型”子项所附元数据的数据字典及处理步骤章节。

本次还开展了7项网格化测量：
密西西比河砾石滩区域：
- 250米线间距：普拉里角（Prairie Point）、63号岛（Island 63）、克拉罗德（Crumrod）
- 100米线间距：怀特河区域
梅尔顿网格（Melton Grid）：位于密西西比州明特城附近区域，共23测线公里，线间距100米。
阿肯色州OSL网格（AR OSL Grid）：位于阿肯色州帕拉古尔德附近的一系列钻孔岩芯位置区域，共268测线公里，线间距500米。
拉库西旧河道网格（Raccourci Grid）：位于路易斯安那州巴切勒附近的废弃牛轭湖拉库西旧河道区域，共100测线公里，线间距可变。

附加数据
本数据发布还包含2018年3月在密西西比州格林维尔附近堤岸区域采集的数据集。本次测量共布设4条平行于堤岸的测线，总长度27测线公里，用于评估针对密西西比河冲积平原与奇科特含水层范围的大规模测量所采用的技术方案。该数据集仅包含航空电磁（Airborne Electromagnetic, AEM）数据，未采集磁法与放射性数据。

关于飞行线路编号以及放射性数据采集与处理所用各类方法的引用信息，详见补充章节。