National Gravity Compilation 2019 DGIR tilt image

Gravity data measure small changes in gravity due to changes in the density of rocks beneath the Earth's surface. The data collected are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This National Gravity Compilation 2019 DGIR tilt image is produced from the 2019 Australian National Gravity Grids A series. These gravity data were acquired under the project No. 202008. The grid has a cell size of 0.00417 degrees (approximately 435m). The %%MV_DATASETS/SURVEY_NAME% are derived from ground observations stored in the Australian National Gravity Database (ANGD) as at September 2019, supplemented by offshore data sourced from v28.1 of the Global Gravity grid developed using data from the Scripps Institution of Oceanography, the National Oceanic and Atmospheric Administration (NOAA), and National Geospatial-Intelligence Agency (NGA) at Scripps Institution of Oceanography, University of California San Diego. Out of the approximately 1.8 million gravity observations, nearly 1.4 million gravity stations in the ANGD together with marine data were used to generate this grid. The ground gravity data used in the national grid has been acquired by the Commonwealth, State and Territory Governments, the mining and exploration industry, universities and research organisations from the 1940's to the present day. Station spacing for ground observations varies from approximately 11 km down to less than 1 km, with major parts of the continent having station spacing between 2.5 and 7 km. The DGIR was obtained by subtracting 3 quantities (i.e., the near-field isostatic correction, the far-field isostatic correction, and a first order trend correction) from Complete Bouguer Anomaly data (CBA) of the 2019 Australian National Gravity Grids A series. The image shows a tilt of the de-trended global isostatic residual (DGIR) anomalies (A series) over Australia and its continental margins. A tilt filter was calculated by applying a fast Fourier transform (FFT) process to the DGIR grid of the 2019 Australian National Gravity Grids A series. A tilt filter is a ratio of the vertical derivative to the total horizontal derivative and is used for detection of edges of geological units.

重力数据用于测量地球表层下方岩石密度变化引发的微小重力场变化。所采集的数据将通过标准流程处理，确保记录的响应仅源于地下岩石的重力效应。经处理得到的数据集可通过解译揭示地下地质构造。经处理的数据将由GA地球物理学家开展质量核验，确保GA发布的最终数据符合使用要求。本次2019年国家重力编绘去趋势全球均衡剩余异常（de-trended global isostatic residual, DGIR）倾斜图像基于2019年澳大利亚国家重力网格A系列生成。本次重力数据采集工作隶属于编号为202008的项目。该网格的单元尺寸为0.00417度（约合435米）。本数据集的%%MV_DATASETS/SURVEY_NAME%源自截至2019年9月存储于澳大利亚国家重力数据库（Australian National Gravity Database, ANGD）的地面观测结果，并辅以来自全球重力网格v28.1版的海洋数据；该全球重力网格的构建数据来自斯克里普斯海洋研究所、美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration, NOAA）以及美国国家地理空间情报局（National Geospatial-Intelligence Agency, NGA），由加州大学圣迭戈分校斯克里普斯海洋研究所开发。本次网格构建共用到约180万条重力观测数据，其中包括ANGD中近140万个重力测点数据以及海洋观测数据。本国家重力网格所用的地面重力数据，采集自20世纪40年代至今的英联邦、各州及领地政府、矿业与勘探行业、高校及科研机构。地面观测的测点间距介于约11公里至不足1公里之间，澳大利亚大陆大部分区域的测点间距处于2.5至7公里范围内。DGIR通过从2019年澳大利亚国家重力网格A系列的完全布格异常（Complete Bouguer Anomaly, CBA）数据中扣除三个校正量（即近场均衡校正、远场均衡校正以及一阶趋势校正）得到。本图像展示了澳大利亚及其大陆边缘区域的DGIR异常（A系列）的倾斜场结果。倾斜滤波器通过对2019年澳大利亚国家重力网格A系列的DGIR网格应用快速傅里叶变换（fast Fourier transform, FFT）流程计算得到。倾斜滤波器为垂直导数与总水平导数的比值，可用于识别地质单元的边界。