Gamma-ray, Magnetic, and Topographic Data for the Colorado Front Range

The grid files presented here are in ASCII format that uses the
definitions of the grid exchange format (GXF). The files can be
viewed using a suitable word processing program. The different
grids are:
>Kfrco.gxf potassium concentrations in the rocks and soils
>Ufrco.gxf uranium concentrations in the rocks and soils
>Thfrco.gxf thorium concentrations in the rocks and soils
>Magfrco.gxf residual magnetic field
>Terrfrco.gxf digital elevations
The data used to create the potassium (K), uranium (U), thorium
(Th), and magnetic (Mag) grids were obtained as part of the
National Uranium Resource Evaluation (NURE) Program of the U.S.
Department of Energy (USDOE). The NURE Program included aerial
surveys that collected gamma-ray and magnetic data. The aerial
surveys were flown at a nominal altitude of 122 meters above the
ground. The aerial survey flightlines were generally flown east-
west with north-south tielines. For the data covering the
mountains of the Colorado Front Range, the flightline spacing is
1 mile (1600 meters) for the east-west lines and about 8 miles
(12.8 km) for the north-south tielines. For the data covering
the plains to the east of the mountains, the flightline spacing
is 3 miles (4800 m) for the east-west lines and about 16 miles
(25.6 km) for the north-south tielines. In the mountains,
helicopters were used with a detector volume of 2000 cubic inches
(32.8 liters) of thallium doped sodium iodide (NaI(Tl)). Over the
plains, fixed-wing aircraft were used with about 3300 cubic
inches (54 liters) of NaI(Tl) detector. The magnetometers used
were proton-precession magnetometers with base stations used to
make diurnal corrections. The USDOE contracted with private
contractors to conduct the aerial surveys and the contractors
were responsible for all aspects of calibration and data
processing.
The data used to create the grid of digital elevations were
derived from the U.S. Geological Survey (USGS) 1:250,000
topographic quadrangle maps. The topographic maps were digitized
at intervals of three arc-seconds and were then averaged to
intervals of 15 seconds. The resulting 15-second data were used
to calculate the grid presented here.
The units of the grid data are:
>Potassium percent K
>Uranium parts per million (ppm) eU
>Thorium ppm eTh
>Magnetic nano Teslas
>Elevation meters

本文提供的网格文件采用ASCII格式，遵循网格交换格式（Grid Exchange Format, GXF）的定义规范。此类文件可通过适配的文字处理程序查看。本次提供的不同网格如下：
>Kfrco.gxf 岩石与土壤中的钾元素浓度
>Ufrco.gxf 岩石与土壤中的铀元素浓度
>Thfrco.gxf 岩石与土壤中的钍元素浓度
>Magfrco.gxf 剩余磁场数据
>Terrfrco.gxf 数字高程数据

用于生成钾（K）、铀（U）、钍（Th）及磁场（Mag）网格的数据，均取自美国能源部（U.S. Department of Energy, USDOE）牵头实施的国家铀资源评估（National Uranium Resource Evaluation, NURE）项目。该项目包含航空测量任务，用于采集伽马射线与磁场数据。本次航空测量的标称飞行高度为地面上方122米，航线基本沿东西向布设，同时辅以南北向联络航线。针对科罗拉多前山山区的测量数据，东西向航线间距为1英里（1600米），南北向联络航线间距约为8英里（12.8千米）；针对山脉东侧平原区域的测量数据，东西向航线间距为3英里（4800米），南北向联络航线间距约为16英里（25.6千米）。

在山区作业时，采用搭载2000立方英寸（32.8升）铊掺杂碘化钠（NaI(Tl)）探测器的直升机开展测量；在平原区域则使用搭载约3300立方英寸（54升）NaI(Tl)探测器的固定翼飞机。本次测量使用的磁力仪为质子进动磁力仪，并配备基准站进行日变校正。美国能源部将航空测量工作外包给私营承包商，由承包商负责校准与数据处理的全部环节。

用于生成数字高程网格的数据，源自美国地质调查局（U.S. Geological Survey, USGS）发布的1:250000地形图图幅。这些地形图图幅以3角秒的间隔进行数字化，随后经平均处理得到15角秒间隔的数据，最终生成的15角秒数据被用于制作本次提供的网格数据。

各网格数据的单位如下：
>钾元素 钾含量百分比（% K）
>铀元素 等效铀百万分比（ppm eU）
>钍元素 等效钍百万分比（ppm eTh）
>磁场数据 纳特斯拉（nT）
>高程数据 米（m）