Tanami NS 5S - TMI RTP 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 magnetic grid has a cell size of 0.00018 degrees (approximately 20m).The data are in nanoTesla (or nT). The data used to produce this grid was acquired in 2018 by the NT Government, and consisted of 15632 line-kilometres of data at 100m 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. This survey grid is essentially levelled to AWAGS.The data has had a variable reduction to the pole applied to centre the magnetic anomaly over the magnetised body. The VRTP processing followed a differential reduction to pole calculation up to 5th order polynomial. Magnetic inclination and declination were derived from the IGRF-11 geomagnetic reference model using a data representative date and elevation representative of the survey.

总磁强度（Total Magnetic Intensity, TMI）数据用于表征由地壳内造岩矿物组分差异所引起的地球磁场强度变化。磁异常可分为正异常（磁场强度高于正常值）与负异常（磁场强度低于正常值），具体取决于岩石的磁化率。本数据集通过标准化流程进行处理，以确保所记录的响应仅源于地下岩石。经处理后得到的数据集可通过解译揭示地下地质构造。经处理的数据已由GA地球物理学家开展质量核查，确保GA发布的最终数据符合使用需求。该磁网格的单元尺寸为0.00018度（约20米），数据单位为纳特斯拉（nanoTesla, nT）。NT政府于2018年采集了用于构建该网格的数据，总测线长度达15632线公里，测线间距为100米，地形离地高度为60米。为约束网格中的长波长成分，项目引入独立数据集：全澳航空地球物理调查（Australia-wide Airborne Geophysical Survey, AWAGS）航空磁数据，用于校正该测网格的基准值。该测网格已基本匹配AWAGS数据完成平差处理。该数据已施加可变化极（Variable Reduction to the Pole, VRTP）处理，使磁异常中心与磁化体位置重合。本次VRTP处理采用差分化极算法，最高可至五阶多项式展开。磁倾角与磁偏角基于IGRF-11地磁参考模型计算得到，计算时采用了与本次调查匹配的代表性日期与高程参数。