Unfiltered Thorium Element Concentrations Image of Australia 2015

This image is unfiltered thorium (Th element concentrations ppm eTh)

he Radiometric Map of Australia dataset comprises grids of potassium (K), uranium (U) and thorium (Th) element concentrations, and derivatives of these grids. The third edition was derived by seamlessly merging 45 new survey grids with the Second Edition Radiometric Map of Australia (Minty et al., 2010).

Details of the specifications of individual airborne surveys can be found in the Fourteenth Edition of the Index of Airborne Geophysical Surveys (Percival, 2014), which is included with the grid as a PDF document. This Index is also available online at http://www.ga.gov.au/metadata-gateway/metadata/record/gcat_f3ad4f15-96bc-0cf3-e044-00144fdd4fa6/Index+of+airborne+geophysical+surveys%3A+14th+edition. Further up to date information about individual surveys can also be obtained online from the Airborne Surveys Database at http://www.ga.gov.au/oracle/argus/.

Matching of the grids in the database was achieved using a program called Gridmerge, which was originally developed within Geoscience Australia and has now been commercialised. This program was used to merge 45 new surveys to the Second Edition Radiometric Map of Australia. The second edition merged over 550 individual grids to create the compilation (Minty et al., 2009) and the Australia-wide Airborne Geophysical Survey (AWAGS) airborne radiometric data was used to control the base levels of those survey grids which overlapped the AWAGS data (Milligan et al., 2009). As the second edition was used as a base grid for the Gridmerge operation the new Third Edition is essentially levelled to AWAGS.

Cell sizes: The cell sizes of the original survey grids range from 50 m through 800 m, but most have a cell size of about 100 m. The 45 original survey grids were levelled and then re-sampled, using Newton 4th Order local operator onto the Second Edition Radiometric Map of Australia Grids with a cell size of about 100m (0.001 degrees).

Filtering: Potassium, uranium, thorium and dose rate grid are available in both filtered and unfiltered versions. The low-pass filtering was achieved by applying a 7-point, degree-3 Savitzky-Golay filter (Savitzky & Golay, 1964) to each of the original survey grids prior to grid merging.

Projections and Datums: The grids are stored as geodetic grids based on the GDA94 datum, but can be re-projected prior to downloading.
Grid downloads: The Radiometric Map of Australia grids can be downloaded using the Geophysical Archive Data Delivery System (GADDS) on the Australian Government's Geoscience Portal at http://www.geoscience.gov.au/gadds

File sizes: At full resolution, each Radiometric Map of Australia grid has 34761 rows and 40954 columns. Each grid has a file size of approximately 5.3 Gb in ERMapper format. Note that, because of the file sizes, GADDS will not allow users to do download the grids at full resolution. Users wishing to access the grids at full resolution should contact Geoscience Australia to make arrangements to have the data supplied on a portable hard drive.

本图像为未经过滤的钍（Th，元素浓度单位：ppm eTh）数据。
澳大利亚放射测量地图数据集包含钾（K）、铀（U）及钍（Th）的元素浓度栅格，以及上述栅格的衍生数据集。该数据集第三版通过将45份新的测量栅格与《澳大利亚放射测量地图（第二版）》（Minty等人，2010）无缝融合而成。

各航空测量项目的规格细节可查阅《航空地球物理测量索引（第十四版）》（Percival，2014），该文档以PDF格式随栅格数据一同提供。此索引也可通过以下网址在线获取：http://www.ga.gov.au/metadata-gateway/metadata/record/gcat_f3ad4f15-96bc-0cf3-e044-00144fdd4fa6/Index+of+airborne+geophysical+surveys%3A+14th+edition。如需获取各测量项目的最新信息，还可通过航空测量数据库的在线平台获取，网址为：http://www.ga.gov.au/oracle/argus/。

数据库中栅格的配准工作通过一款名为Gridmerge的程序完成，该程序最初由澳大利亚地球科学局开发，目前已实现商业化。此程序被用于将45份新的测量栅格融合至《澳大利亚放射测量地图（第二版）》。第二版融合了超过550份独立栅格以完成数据集汇编（Minty等人，2009），而覆盖全澳航空地球物理测量（AWAGS）的航空放射测量数据被用于校准与AWAGS数据重叠的测量栅格的基准水平（Milligan等人，2009）。由于第二版被用作Gridmerge操作的基础栅格，全新的第三版本质上已按照AWAGS标准完成了水平校准。

栅格分辨率：原始测量栅格的单元格尺寸范围为50米至800米，其中多数约为100米。本次45份原始测量栅格均完成了水平校准，并通过牛顿四阶局部算子重采样至分辨率约为100米（0.001度）的《澳大利亚放射测量地图（第二版）》栅格坐标系。

滤波处理：钾、铀、钍及剂量率栅格均提供滤波版与未滤波版两种版本。低通滤波通过在栅格融合前，对每份原始测量栅格应用7点3阶萨维茨基-戈莱（Savitzky-Golay）滤波器实现（Savitzky & Golay，1964）。

投影与基准面：栅格以基于GDA94基准面的大地测量栅格格式存储，用户可在下载前对其进行重投影操作。

栅格下载：澳大利亚放射测量地图栅格可通过澳大利亚政府地球科学门户网站上的地球科学档案数据交付系统（Geophysical Archive Data Delivery System, GADDS）进行下载，网址为：http://www.geoscience.gov.au/gadds。

文件大小：全分辨率下，每份澳大利亚放射测量地图栅格包含34761行与40954列。ERMapper格式下，每份栅格的文件大小约为5.3 GB。请注意，受限于文件体积，GADDS不支持用户下载全分辨率栅格。如需获取全分辨率栅格，用户需联系澳大利亚地球科学局，协商通过便携式硬盘获取数据的相关事宜。