Spencer - TMI grid (AWAGS)

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 Spencer - TMI grid (AWAGS) has a cell size of 0.0004 degrees (approximately 41m). The units are in nanoTesla (or nT). The data used to produce this grid was acquired in 2018 by the SA Government, and consisted of 49937 line-kilometres of data at 200m line spacing and 60m terrain clearance. To constrain long wavelengths in the grid, an independent data set, the Australia-wide Airborne Geophysical Survey (AWAGS) airborne magnetic data, was used to control the base levels of the survey grid.总磁强度（Total Magnetic Intensity，TMI）数据用于衡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），其类型取决于岩石的磁化率。该数据已通过标准流程进行处理，以确保所记录的响应仅由地下岩石所产生。经处理后得到的数据集可通过解译，揭示地下地质构造。经处理的数据会由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需求。本次的斯宾塞-TMI格网（AWAGS）的格网单元尺寸为0.0004度（约合41米），数据单位为纳特斯拉（nanoTesla，nT）。制作该格网所用的数据由南澳大利亚政府于2018年采集，总测线长度达49937千米，测线间距为200米，地形离地高度为60米。为约束格网中的长波长分量，项目采用了独立数据集——全澳航空地球物理调查（Australia-wide Airborne Geophysical Survey，AWAGS）航空磁测数据，来管控本次调查格网的基准水平。