Magnetic Anomaly Map of Australia, Seventh Edition, 2020 - Enhanced Products Package - TMI RTP 0.5VD grid

Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data 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 Magnetic Anomaly Map of Australia, Seventh Edition, 2020 - Enhanced Products Package - TMI RTP 0.5VD grid is a half vertical derivative of the Total Magnetic Intensity grid for the Magnetic Anomaly Map of Australia, Seventh Edition, 2019. The 2019 Total magnetic Intensity (TMI) grid of Australia has a grid cell size of ~3 seconds of arc (approximately 80 m). This grid only includes airborne-derived TMI data for onshore and near-offshore continental areas.Since the sixth edition was released in 2015, data from 234 new surveys have been added to the database, acquired mainly by the State and Territory Geological Surveys. The new grid was derived from a re-levelling of the national magnetic grid database. The survey grids were levelled to each other, and to the Australia Wide Airborne Geophysical Survey (AWAGS), which serves as a baseline to constrain long wavelengths in the final grid. It is estimated that 33 500 000 line-kilometres of survey data were acquired to produce the 2019 grid data, about 2 000 000 line-kilometres more than for the previous edition. The grid has units of nanoTesla per km (or nT/km). The RTP processing followed a differential reduction to pole calculation up to 5th order polynomial. Magnetic inclination and declination were derived from the IGRF-15 geomagnetic reference model using a data representative date and elevation representative of the survey. A Fast Fourier Transform (FFT) process was applied to the original grid to calculate the half vertical derivative grid.

总磁场强度（Total Magnetic Intensity, TMI）数据用于测量由地壳中成岩矿物成分差异所引发的地球磁场强度变化。磁异常可分为正异常（磁场强度高于正常水平）与负异常（磁场强度低于正常水平），具体取决于岩石的磁化率。该数据通过标准流程进行处理，以确保记录的响应仅源自地下岩石。经处理后得到的数据集可用于解译，以揭示地下地质结构。经处理的数据由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《澳大利亚磁异常图（第七版，2020）- 增强产品包 - TMI 化极（Reduction to Pole, RTP）0.5VD格网》是2019年第七版《澳大利亚磁异常图》总磁场强度格网的半垂直导数格网。2019年澳大利亚总磁场强度（TMI）格网的格网单元尺寸约为3角秒（对应地面约80米）。该格网仅涵盖陆上及近岸陆地区域的航空测量TMI数据。
自2015年第六版发布以来，数据库新增了234项新测量获取的数据，这些数据主要由各州及领地地质调查机构采集。新格网源自对国家磁场格网数据库的重新平差处理。各测量格网之间以及与全澳航空地球物理测量（Australia Wide Airborne Geophysical Survey, AWAGS）进行了平差，后者作为基准约束最终格网中的长波长分量。据估算，为生成2019版格网数据，共采集了3350万测线公里的测量数据，较前一版本增加约200万测线公里。该格网的单位为纳特斯拉每公里（nT/km）。RTP处理采用了最高至5阶多项式的差分化极计算方法。磁场倾角与偏角源自IGRF-15地磁参考模型（IGRF-15 geomagnetic reference model），所用的代表日期与高程均对应测量活动的典型参数。通过对原始格网应用快速傅里叶变换（Fast Fourier Transform, FFT）流程，计算得到半垂直导数格网。