National Gravity Compilation 2019 includes airborne DGIR 0.5VD grid

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 includes airborne DGIR 0.5VD grid is produced from the 2019 Australian National Gravity Grids B series. These gravity data were acquired under the project No. 202008. The grid has a cell size of 0.00417 degrees (approximately 435m). The data 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. Airborne gravity and gravity gradiometry data were also included to provide better resolution to areas where ground gravity data was not of a suitable quality. Out of the approximately 1.8 million gravity observations, nearly 1.4 million gravity stations in the ANGD together with Airborne Gravity surveys totaling 345,000 line km and 106,000 line km of Airborne Gravity Gradiometry were used to generate this grid. The ground and airborne gravity data used in this 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. Airborne surveys have a line spacing ranging from 0.5 km to 2.5 km. The grid shows the half vertical derivative of the de-trended global isostatic residual (DGIR) anomalies over Australia and its continental margins. The DGIR grid 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 B series. A half vertical derivative was calculated by applying a fast Fourier transform (FFT) process to the DGIR grid of the 2019 Australian National Gravity Grids to produce this grid.

重力数据用于测量因地球表层下方岩石密度变化而产生的微小重力变化。所采集的数据将通过标准流程进行处理，以确保记录的响应仅源于地下岩石的影响。处理后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查，以确保GA发布的最终数据符合使用要求。本次2019年国家重力编图成果包含基于2019年澳大利亚国家重力格网B系列生成的航空DGIR 0.5VD格网，该批重力数据采集自项目编号202008，该格网的单元格大小为0.00417度（约合435米）。本次数据源自截至2019年9月存储于澳大利亚国家重力数据库（Australian National Gravity Database, ANGD）的地面观测数据，并辅以来自全球重力格网v28.1的海上数据；该全球重力格网基于美国加州大学圣迭戈分校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）提供的数据构建而成。同时纳入航空重力及重力梯度测量数据，以提升地面重力数据质量欠佳区域的解译分辨率。在约180万条重力观测数据中，本次格网生成使用了ANGD中近140万个重力测点，以及总长34.5万测线公里的航空重力测量数据与10.6万测线公里的航空重力梯度测量数据。本次格网所用的地面及航空重力数据，采集时间跨度自20世纪40年代至今，数据来源包括联邦、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公里至7公里区间，航空测量的测线间距介于0.5公里至2.5公里之间。该格网展示了澳大利亚及其大陆边缘区域的去趋势全球均衡剩余（de-trended Global Isostatic Residual, DGIR）异常的半垂直导数。DGIR格网通过从2019年澳大利亚国家重力格网B系列的完整布格异常（Complete Bouguer Anomaly, CBA）数据中扣除三项校正量（即近场均衡校正、远场均衡校正以及一阶趋势校正）得到。本次格网的生成，是通过对2019年澳大利亚国家重力格网的DGIR格网应用快速傅里叶变换（Fast Fourier Transform, FFT）算法计算得到半垂直导数。